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Linux/Documentation/admin-guide/media/vivid.rst

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  1 .. SPDX-License-Identifier: GPL-2.0
  2 
  3 The Virtual Video Test Driver (vivid)
  4 =====================================
  5 
  6 This driver emulates video4linux hardware of various types: video capture, video
  7 output, vbi capture and output, metadata capture and output, radio receivers and
  8 transmitters, touch capture and a software defined radio receiver. In addition a
  9 simple framebuffer device is available for testing capture and output overlays.
 10 
 11 Up to 64 vivid instances can be created, each with up to 16 inputs and 16 outputs.
 12 
 13 Each input can be a webcam, TV capture device, S-Video capture device or an HDMI
 14 capture device. Each output can be an S-Video output device or an HDMI output
 15 device.
 16 
 17 These inputs and outputs act exactly as a real hardware device would behave. This
 18 allows you to use this driver as a test input for application development, since
 19 you can test the various features without requiring special hardware.
 20 
 21 This document describes the features implemented by this driver:
 22 
 23 - Support for read()/write(), MMAP, USERPTR and DMABUF streaming I/O.
 24 - A large list of test patterns and variations thereof
 25 - Working brightness, contrast, saturation and hue controls
 26 - Support for the alpha color component
 27 - Full colorspace support, including limited/full RGB range
 28 - All possible control types are present
 29 - Support for various pixel aspect ratios and video aspect ratios
 30 - Error injection to test what happens if errors occur
 31 - Supports crop/compose/scale in any combination for both input and output
 32 - Can emulate up to 4K resolutions
 33 - All Field settings are supported for testing interlaced capturing
 34 - Supports all standard YUV and RGB formats, including two multiplanar YUV formats
 35 - Raw and Sliced VBI capture and output support
 36 - Radio receiver and transmitter support, including RDS support
 37 - Software defined radio (SDR) support
 38 - Capture and output overlay support
 39 - Metadata capture and output support
 40 - Touch capture support
 41 
 42 These features will be described in more detail below.
 43 
 44 Configuring the driver
 45 ----------------------
 46 
 47 By default the driver will create a single instance that has a video capture
 48 device with webcam, TV, S-Video and HDMI inputs, a video output device with
 49 S-Video and HDMI outputs, one vbi capture device, one vbi output device, one
 50 radio receiver device, one radio transmitter device and one SDR device.
 51 
 52 The number of instances, devices, video inputs and outputs and their types are
 53 all configurable using the following module options:
 54 
 55 - n_devs:
 56 
 57         number of driver instances to create. By default set to 1. Up to 64
 58         instances can be created.
 59 
 60 - node_types:
 61 
 62         which devices should each driver instance create. An array of
 63         hexadecimal values, one for each instance. The default is 0xe1d3d.
 64         Each value is a bitmask with the following meaning:
 65 
 66                 - bit 0: Video Capture node
 67                 - bit 2-3: VBI Capture node: 0 = none, 1 = raw vbi, 2 = sliced vbi, 3 = both
 68                 - bit 4: Radio Receiver node
 69                 - bit 5: Software Defined Radio Receiver node
 70                 - bit 8: Video Output node
 71                 - bit 10-11: VBI Output node: 0 = none, 1 = raw vbi, 2 = sliced vbi, 3 = both
 72                 - bit 12: Radio Transmitter node
 73                 - bit 16: Framebuffer for testing overlays
 74                 - bit 17: Metadata Capture node
 75                 - bit 18: Metadata Output node
 76                 - bit 19: Touch Capture node
 77 
 78         So to create four instances, the first two with just one video capture
 79         device, the second two with just one video output device you would pass
 80         these module options to vivid:
 81 
 82         .. code-block:: none
 83 
 84                 n_devs=4 node_types=0x1,0x1,0x100,0x100
 85 
 86 - num_inputs:
 87 
 88         the number of inputs, one for each instance. By default 4 inputs
 89         are created for each video capture device. At most 16 inputs can be created,
 90         and there must be at least one.
 91 
 92 - input_types:
 93 
 94         the input types for each instance, the default is 0xe4. This defines
 95         what the type of each input is when the inputs are created for each driver
 96         instance. This is a hexadecimal value with up to 16 pairs of bits, each
 97         pair gives the type and bits 0-1 map to input 0, bits 2-3 map to input 1,
 98         30-31 map to input 15. Each pair of bits has the following meaning:
 99 
100                 - 00: this is a webcam input
101                 - 01: this is a TV tuner input
102                 - 10: this is an S-Video input
103                 - 11: this is an HDMI input
104 
105         So to create a video capture device with 8 inputs where input 0 is a TV
106         tuner, inputs 1-3 are S-Video inputs and inputs 4-7 are HDMI inputs you
107         would use the following module options:
108 
109         .. code-block:: none
110 
111                 num_inputs=8 input_types=0xffa9
112 
113 - num_outputs:
114 
115         the number of outputs, one for each instance. By default 2 outputs
116         are created for each video output device. At most 16 outputs can be
117         created, and there must be at least one.
118 
119 - output_types:
120 
121         the output types for each instance, the default is 0x02. This defines
122         what the type of each output is when the outputs are created for each
123         driver instance. This is a hexadecimal value with up to 16 bits, each bit
124         gives the type and bit 0 maps to output 0, bit 1 maps to output 1, bit
125         15 maps to output 15. The meaning of each bit is as follows:
126 
127                 - 0: this is an S-Video output
128                 - 1: this is an HDMI output
129 
130         So to create a video output device with 8 outputs where outputs 0-3 are
131         S-Video outputs and outputs 4-7 are HDMI outputs you would use the
132         following module options:
133 
134         .. code-block:: none
135 
136                 num_outputs=8 output_types=0xf0
137 
138 - vid_cap_nr:
139 
140         give the desired videoX start number for each video capture device.
141         The default is -1 which will just take the first free number. This allows
142         you to map capture video nodes to specific videoX device nodes. Example:
143 
144         .. code-block:: none
145 
146                 n_devs=4 vid_cap_nr=2,4,6,8
147 
148         This will attempt to assign /dev/video2 for the video capture device of
149         the first vivid instance, video4 for the next up to video8 for the last
150         instance. If it can't succeed, then it will just take the next free
151         number.
152 
153 - vid_out_nr:
154 
155         give the desired videoX start number for each video output device.
156         The default is -1 which will just take the first free number.
157 
158 - vbi_cap_nr:
159 
160         give the desired vbiX start number for each vbi capture device.
161         The default is -1 which will just take the first free number.
162 
163 - vbi_out_nr:
164 
165         give the desired vbiX start number for each vbi output device.
166         The default is -1 which will just take the first free number.
167 
168 - radio_rx_nr:
169 
170         give the desired radioX start number for each radio receiver device.
171         The default is -1 which will just take the first free number.
172 
173 - radio_tx_nr:
174 
175         give the desired radioX start number for each radio transmitter
176         device. The default is -1 which will just take the first free number.
177 
178 - sdr_cap_nr:
179 
180         give the desired swradioX start number for each SDR capture device.
181         The default is -1 which will just take the first free number.
182 
183 - meta_cap_nr:
184 
185         give the desired videoX start number for each metadata capture device.
186         The default is -1 which will just take the first free number.
187 
188 - meta_out_nr:
189 
190         give the desired videoX start number for each metadata output device.
191         The default is -1 which will just take the first free number.
192 
193 - touch_cap_nr:
194 
195         give the desired v4l-touchX start number for each touch capture device.
196         The default is -1 which will just take the first free number.
197 
198 - ccs_cap_mode:
199 
200         specify the allowed video capture crop/compose/scaling combination
201         for each driver instance. Video capture devices can have any combination
202         of cropping, composing and scaling capabilities and this will tell the
203         vivid driver which of those is should emulate. By default the user can
204         select this through controls.
205 
206         The value is either -1 (controlled by the user) or a set of three bits,
207         each enabling (1) or disabling (0) one of the features:
208 
209         - bit 0:
210 
211                 Enable crop support. Cropping will take only part of the
212                 incoming picture.
213         - bit 1:
214 
215                 Enable compose support. Composing will copy the incoming
216                 picture into a larger buffer.
217 
218         - bit 2:
219 
220                 Enable scaling support. Scaling can scale the incoming
221                 picture. The scaler of the vivid driver can enlarge up
222                 or down to four times the original size. The scaler is
223                 very simple and low-quality. Simplicity and speed were
224                 key, not quality.
225 
226         Note that this value is ignored by webcam inputs: those enumerate
227         discrete framesizes and that is incompatible with cropping, composing
228         or scaling.
229 
230 - ccs_out_mode:
231 
232         specify the allowed video output crop/compose/scaling combination
233         for each driver instance. Video output devices can have any combination
234         of cropping, composing and scaling capabilities and this will tell the
235         vivid driver which of those is should emulate. By default the user can
236         select this through controls.
237 
238         The value is either -1 (controlled by the user) or a set of three bits,
239         each enabling (1) or disabling (0) one of the features:
240 
241         - bit 0:
242 
243                 Enable crop support. Cropping will take only part of the
244                 outgoing buffer.
245 
246         - bit 1:
247 
248                 Enable compose support. Composing will copy the incoming
249                 buffer into a larger picture frame.
250 
251         - bit 2:
252 
253                 Enable scaling support. Scaling can scale the incoming
254                 buffer. The scaler of the vivid driver can enlarge up
255                 or down to four times the original size. The scaler is
256                 very simple and low-quality. Simplicity and speed were
257                 key, not quality.
258 
259 - multiplanar:
260 
261         select whether each device instance supports multi-planar formats,
262         and thus the V4L2 multi-planar API. By default device instances are
263         single-planar.
264 
265         This module option can override that for each instance. Values are:
266 
267                 - 1: this is a single-planar instance.
268                 - 2: this is a multi-planar instance.
269 
270 - vivid_debug:
271 
272         enable driver debugging info
273 
274 - no_error_inj:
275 
276         if set disable the error injecting controls. This option is
277         needed in order to run a tool like v4l2-compliance. Tools like that
278         exercise all controls including a control like 'Disconnect' which
279         emulates a USB disconnect, making the device inaccessible and so
280         all tests that v4l2-compliance is doing will fail afterwards.
281 
282         There may be other situations as well where you want to disable the
283         error injection support of vivid. When this option is set, then the
284         controls that select crop, compose and scale behavior are also
285         removed. Unless overridden by ccs_cap_mode and/or ccs_out_mode the
286         will default to enabling crop, compose and scaling.
287 
288 - allocators:
289 
290         memory allocator selection, default is 0. It specifies the way buffers
291         will be allocated.
292 
293                 - 0: vmalloc
294                 - 1: dma-contig
295 
296 - cache_hints:
297 
298         specifies if the device should set queues' user-space cache and memory
299         consistency hint capability (V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS).
300         The hints are valid only when using MMAP streaming I/O. Default is 0.
301 
302                 - 0: forbid hints
303                 - 1: allow hints
304 
305 - supports_requests:
306 
307         specifies if the device should support the Request API. There are
308         three possible values, default is 1:
309 
310                 - 0: no request
311                 - 1: supports requests
312                 - 2: requires requests
313 
314 Taken together, all these module options allow you to precisely customize
315 the driver behavior and test your application with all sorts of permutations.
316 It is also very suitable to emulate hardware that is not yet available, e.g.
317 when developing software for a new upcoming device.
318 
319 
320 Video Capture
321 -------------
322 
323 This is probably the most frequently used feature. The video capture device
324 can be configured by using the module options num_inputs, input_types and
325 ccs_cap_mode (see "Configuring the driver" for more detailed information),
326 but by default four inputs are configured: a webcam, a TV tuner, an S-Video
327 and an HDMI input, one input for each input type. Those are described in more
328 detail below.
329 
330 Special attention has been given to the rate at which new frames become
331 available. The jitter will be around 1 jiffy (that depends on the HZ
332 configuration of your kernel, so usually 1/100, 1/250 or 1/1000 of a second),
333 but the long-term behavior is exactly following the framerate. So a
334 framerate of 59.94 Hz is really different from 60 Hz. If the framerate
335 exceeds your kernel's HZ value, then you will get dropped frames, but the
336 frame/field sequence counting will keep track of that so the sequence
337 count will skip whenever frames are dropped.
338 
339 
340 Webcam Input
341 ~~~~~~~~~~~~
342 
343 The webcam input supports three framesizes: 320x180, 640x360 and 1280x720. It
344 supports frames per second settings of 10, 15, 25, 30, 50 and 60 fps. Which ones
345 are available depends on the chosen framesize: the larger the framesize, the
346 lower the maximum frames per second.
347 
348 The initially selected colorspace when you switch to the webcam input will be
349 sRGB.
350 
351 
352 TV and S-Video Inputs
353 ~~~~~~~~~~~~~~~~~~~~~
354 
355 The only difference between the TV and S-Video input is that the TV has a
356 tuner. Otherwise they behave identically.
357 
358 These inputs support audio inputs as well: one TV and one Line-In. They
359 both support all TV standards. If the standard is queried, then the Vivid
360 controls 'Standard Signal Mode' and 'Standard' determine what
361 the result will be.
362 
363 These inputs support all combinations of the field setting. Special care has
364 been taken to faithfully reproduce how fields are handled for the different
365 TV standards. This is particularly noticeable when generating a horizontally
366 moving image so the temporal effect of using interlaced formats becomes clearly
367 visible. For 50 Hz standards the top field is the oldest and the bottom field
368 is the newest in time. For 60 Hz standards that is reversed: the bottom field
369 is the oldest and the top field is the newest in time.
370 
371 When you start capturing in V4L2_FIELD_ALTERNATE mode the first buffer will
372 contain the top field for 50 Hz standards and the bottom field for 60 Hz
373 standards. This is what capture hardware does as well.
374 
375 Finally, for PAL/SECAM standards the first half of the top line contains noise.
376 This simulates the Wide Screen Signal that is commonly placed there.
377 
378 The initially selected colorspace when you switch to the TV or S-Video input
379 will be SMPTE-170M.
380 
381 The pixel aspect ratio will depend on the TV standard. The video aspect ratio
382 can be selected through the 'Standard Aspect Ratio' Vivid control.
383 Choices are '4x3', '16x9' which will give letterboxed widescreen video and
384 '16x9 Anamorphic' which will give full screen squashed anamorphic widescreen
385 video that will need to be scaled accordingly.
386 
387 The TV 'tuner' supports a frequency range of 44-958 MHz. Channels are available
388 every 6 MHz, starting from 49.25 MHz. For each channel the generated image
389 will be in color for the +/- 0.25 MHz around it, and in grayscale for
390 +/- 1 MHz around the channel. Beyond that it is just noise. The VIDIOC_G_TUNER
391 ioctl will return 100% signal strength for +/- 0.25 MHz and 50% for +/- 1 MHz.
392 It will also return correct afc values to show whether the frequency is too
393 low or too high.
394 
395 The audio subchannels that are returned are MONO for the +/- 1 MHz range around
396 a valid channel frequency. When the frequency is within +/- 0.25 MHz of the
397 channel it will return either MONO, STEREO, either MONO | SAP (for NTSC) or
398 LANG1 | LANG2 (for others), or STEREO | SAP.
399 
400 Which one is returned depends on the chosen channel, each next valid channel
401 will cycle through the possible audio subchannel combinations. This allows
402 you to test the various combinations by just switching channels..
403 
404 Finally, for these inputs the v4l2_timecode struct is filled in the
405 dequeued v4l2_buffer struct.
406 
407 
408 HDMI Input
409 ~~~~~~~~~~
410 
411 The HDMI inputs supports all CEA-861 and DMT timings, both progressive and
412 interlaced, for pixelclock frequencies between 25 and 600 MHz. The field
413 mode for interlaced formats is always V4L2_FIELD_ALTERNATE. For HDMI the
414 field order is always top field first, and when you start capturing an
415 interlaced format you will receive the top field first.
416 
417 The initially selected colorspace when you switch to the HDMI input or
418 select an HDMI timing is based on the format resolution: for resolutions
419 less than or equal to 720x576 the colorspace is set to SMPTE-170M, for
420 others it is set to REC-709 (CEA-861 timings) or sRGB (VESA DMT timings).
421 
422 The pixel aspect ratio will depend on the HDMI timing: for 720x480 is it
423 set as for the NTSC TV standard, for 720x576 it is set as for the PAL TV
424 standard, and for all others a 1:1 pixel aspect ratio is returned.
425 
426 The video aspect ratio can be selected through the 'DV Timings Aspect Ratio'
427 Vivid control. Choices are 'Source Width x Height' (just use the
428 same ratio as the chosen format), '4x3' or '16x9', either of which can
429 result in pillarboxed or letterboxed video.
430 
431 For HDMI inputs it is possible to set the EDID. By default a simple EDID
432 is provided. You can only set the EDID for HDMI inputs. Internally, however,
433 the EDID is shared between all HDMI inputs.
434 
435 No interpretation is done of the EDID data with the exception of the
436 physical address. See the CEC section for more details.
437 
438 There is a maximum of 15 HDMI inputs (if there are more, then they will be
439 reduced to 15) since that's the limitation of the EDID physical address.
440 
441 
442 Video Output
443 ------------
444 
445 The video output device can be configured by using the module options
446 num_outputs, output_types and ccs_out_mode (see "Configuring the driver"
447 for more detailed information), but by default two outputs are configured:
448 an S-Video and an HDMI input, one output for each output type. Those are
449 described in more detail below.
450 
451 Like with video capture the framerate is also exact in the long term.
452 
453 
454 S-Video Output
455 ~~~~~~~~~~~~~~
456 
457 This output supports audio outputs as well: "Line-Out 1" and "Line-Out 2".
458 The S-Video output supports all TV standards.
459 
460 This output supports all combinations of the field setting.
461 
462 The initially selected colorspace when you switch to the TV or S-Video input
463 will be SMPTE-170M.
464 
465 
466 HDMI Output
467 ~~~~~~~~~~~
468 
469 The HDMI output supports all CEA-861 and DMT timings, both progressive and
470 interlaced, for pixelclock frequencies between 25 and 600 MHz. The field
471 mode for interlaced formats is always V4L2_FIELD_ALTERNATE.
472 
473 The initially selected colorspace when you switch to the HDMI output or
474 select an HDMI timing is based on the format resolution: for resolutions
475 less than or equal to 720x576 the colorspace is set to SMPTE-170M, for
476 others it is set to REC-709 (CEA-861 timings) or sRGB (VESA DMT timings).
477 
478 The pixel aspect ratio will depend on the HDMI timing: for 720x480 is it
479 set as for the NTSC TV standard, for 720x576 it is set as for the PAL TV
480 standard, and for all others a 1:1 pixel aspect ratio is returned.
481 
482 An HDMI output has a valid EDID which can be obtained through VIDIOC_G_EDID.
483 
484 There is a maximum of 15 HDMI outputs (if there are more, then they will be
485 reduced to 15) since that's the limitation of the EDID physical address. See
486 also the CEC section for more details.
487 
488 VBI Capture
489 -----------
490 
491 There are three types of VBI capture devices: those that only support raw
492 (undecoded) VBI, those that only support sliced (decoded) VBI and those that
493 support both. This is determined by the node_types module option. In all
494 cases the driver will generate valid VBI data: for 60 Hz standards it will
495 generate Closed Caption and XDS data. The closed caption stream will
496 alternate between "Hello world!" and "Closed captions test" every second.
497 The XDS stream will give the current time once a minute. For 50 Hz standards
498 it will generate the Wide Screen Signal which is based on the actual Video
499 Aspect Ratio control setting and teletext pages 100-159, one page per frame.
500 
501 The VBI device will only work for the S-Video and TV inputs, it will give
502 back an error if the current input is a webcam or HDMI.
503 
504 
505 VBI Output
506 ----------
507 
508 There are three types of VBI output devices: those that only support raw
509 (undecoded) VBI, those that only support sliced (decoded) VBI and those that
510 support both. This is determined by the node_types module option.
511 
512 The sliced VBI output supports the Wide Screen Signal and the teletext signal
513 for 50 Hz standards and Closed Captioning + XDS for 60 Hz standards.
514 
515 The VBI device will only work for the S-Video output, it will give
516 back an error if the current output is HDMI.
517 
518 
519 Radio Receiver
520 --------------
521 
522 The radio receiver emulates an FM/AM/SW receiver. The FM band also supports RDS.
523 The frequency ranges are:
524 
525         - FM: 64 MHz - 108 MHz
526         - AM: 520 kHz - 1710 kHz
527         - SW: 2300 kHz - 26.1 MHz
528 
529 Valid channels are emulated every 1 MHz for FM and every 100 kHz for AM and SW.
530 The signal strength decreases the further the frequency is from the valid
531 frequency until it becomes 0% at +/- 50 kHz (FM) or 5 kHz (AM/SW) from the
532 ideal frequency. The initial frequency when the driver is loaded is set to
533 95 MHz.
534 
535 The FM receiver supports RDS as well, both using 'Block I/O' and 'Controls'
536 modes. In the 'Controls' mode the RDS information is stored in read-only
537 controls. These controls are updated every time the frequency is changed,
538 or when the tuner status is requested. The Block I/O method uses the read()
539 interface to pass the RDS blocks on to the application for decoding.
540 
541 The RDS signal is 'detected' for +/- 12.5 kHz around the channel frequency,
542 and the further the frequency is away from the valid frequency the more RDS
543 errors are randomly introduced into the block I/O stream, up to 50% of all
544 blocks if you are +/- 12.5 kHz from the channel frequency. All four errors
545 can occur in equal proportions: blocks marked 'CORRECTED', blocks marked
546 'ERROR', blocks marked 'INVALID' and dropped blocks.
547 
548 The generated RDS stream contains all the standard fields contained in a
549 0B group, and also radio text and the current time.
550 
551 The receiver supports HW frequency seek, either in Bounded mode, Wrap Around
552 mode or both, which is configurable with the "Radio HW Seek Mode" control.
553 
554 
555 Radio Transmitter
556 -----------------
557 
558 The radio transmitter emulates an FM/AM/SW transmitter. The FM band also supports RDS.
559 The frequency ranges are:
560 
561         - FM: 64 MHz - 108 MHz
562         - AM: 520 kHz - 1710 kHz
563         - SW: 2300 kHz - 26.1 MHz
564 
565 The initial frequency when the driver is loaded is 95.5 MHz.
566 
567 The FM transmitter supports RDS as well, both using 'Block I/O' and 'Controls'
568 modes. In the 'Controls' mode the transmitted RDS information is configured
569 using controls, and in 'Block I/O' mode the blocks are passed to the driver
570 using write().
571 
572 
573 Software Defined Radio Receiver
574 -------------------------------
575 
576 The SDR receiver has three frequency bands for the ADC tuner:
577 
578         - 300 kHz
579         - 900 kHz - 2800 kHz
580         - 3200 kHz
581 
582 The RF tuner supports 50 MHz - 2000 MHz.
583 
584 The generated data contains the In-phase and Quadrature components of a
585 1 kHz tone that has an amplitude of sqrt(2).
586 
587 
588 Metadata Capture
589 ----------------
590 
591 The Metadata capture generates UVC format metadata. The PTS and SCR are
592 transmitted based on the values set in vivid controls.
593 
594 The Metadata device will only work for the Webcam input, it will give
595 back an error for all other inputs.
596 
597 
598 Metadata Output
599 ---------------
600 
601 The Metadata output can be used to set brightness, contrast, saturation and hue.
602 
603 The Metadata device will only work for the Webcam output, it will give
604 back an error for all other outputs.
605 
606 
607 Touch Capture
608 -------------
609 
610 The Touch capture generates touch patterns simulating single tap, double tap,
611 triple tap, move from left to right, zoom in, zoom out, palm press (simulating
612 a large area being pressed on a touchpad), and simulating 16 simultaneous
613 touch points.
614 
615 Controls
616 --------
617 
618 Different devices support different controls. The sections below will describe
619 each control and which devices support them.
620 
621 
622 User Controls - Test Controls
623 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
624 
625 The Button, Boolean, Integer 32 Bits, Integer 64 Bits, Menu, String, Bitmask and
626 Integer Menu are controls that represent all possible control types. The Menu
627 control and the Integer Menu control both have 'holes' in their menu list,
628 meaning that one or more menu items return EINVAL when VIDIOC_QUERYMENU is called.
629 Both menu controls also have a non-zero minimum control value.  These features
630 allow you to check if your application can handle such things correctly.
631 These controls are supported for every device type.
632 
633 
634 User Controls - Video Capture
635 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
636 
637 The following controls are specific to video capture.
638 
639 The Brightness, Contrast, Saturation and Hue controls actually work and are
640 standard. There is one special feature with the Brightness control: each
641 video input has its own brightness value, so changing input will restore
642 the brightness for that input. In addition, each video input uses a different
643 brightness range (minimum and maximum control values). Switching inputs will
644 cause a control event to be sent with the V4L2_EVENT_CTRL_CH_RANGE flag set.
645 This allows you to test controls that can change their range.
646 
647 The 'Gain, Automatic' and Gain controls can be used to test volatile controls:
648 if 'Gain, Automatic' is set, then the Gain control is volatile and changes
649 constantly. If 'Gain, Automatic' is cleared, then the Gain control is a normal
650 control.
651 
652 The 'Horizontal Flip' and 'Vertical Flip' controls can be used to flip the
653 image. These combine with the 'Sensor Flipped Horizontally/Vertically' Vivid
654 controls.
655 
656 The 'Alpha Component' control can be used to set the alpha component for
657 formats containing an alpha channel.
658 
659 
660 User Controls - Audio
661 ~~~~~~~~~~~~~~~~~~~~~
662 
663 The following controls are specific to video capture and output and radio
664 receivers and transmitters.
665 
666 The 'Volume' and 'Mute' audio controls are typical for such devices to
667 control the volume and mute the audio. They don't actually do anything in
668 the vivid driver.
669 
670 
671 Vivid Controls
672 ~~~~~~~~~~~~~~
673 
674 These vivid custom controls control the image generation, error injection, etc.
675 
676 
677 Test Pattern Controls
678 ^^^^^^^^^^^^^^^^^^^^^
679 
680 The Test Pattern Controls are all specific to video capture.
681 
682 - Test Pattern:
683 
684         selects which test pattern to use. Use the CSC Colorbar for
685         testing colorspace conversions: the colors used in that test pattern
686         map to valid colors in all colorspaces. The colorspace conversion
687         is disabled for the other test patterns.
688 
689 - OSD Text Mode:
690 
691         selects whether the text superimposed on the
692         test pattern should be shown, and if so, whether only counters should
693         be displayed or the full text.
694 
695 - Horizontal Movement:
696 
697         selects whether the test pattern should
698         move to the left or right and at what speed.
699 
700 - Vertical Movement:
701 
702         does the same for the vertical direction.
703 
704 - Show Border:
705 
706         show a two-pixel wide border at the edge of the actual image,
707         excluding letter or pillarboxing.
708 
709 - Show Square:
710 
711         show a square in the middle of the image. If the image is
712         displayed with the correct pixel and image aspect ratio corrections,
713         then the width and height of the square on the monitor should be
714         the same.
715 
716 - Insert SAV Code in Image:
717 
718         adds a SAV (Start of Active Video) code to the image.
719         This can be used to check if such codes in the image are inadvertently
720         interpreted instead of being ignored.
721 
722 - Insert EAV Code in Image:
723 
724         does the same for the EAV (End of Active Video) code.
725 
726 - Insert Video Guard Band
727 
728         adds 4 columns of pixels with the HDMI Video Guard Band code at the
729         left hand side of the image. This only works with 3 or 4 byte RGB pixel
730         formats. The RGB pixel value 0xab/0x55/0xab turns out to be equivalent
731         to the HDMI Video Guard Band code that precedes each active video line
732         (see section 5.2.2.1 in the HDMI 1.3 Specification). To test if a video
733         receiver has correct HDMI Video Guard Band processing, enable this
734         control and then move the image to the left hand side of the screen.
735         That will result in video lines that start with multiple pixels that
736         have the same value as the Video Guard Band that precedes them.
737         Receivers that will just keep skipping Video Guard Band values will
738         now fail and either loose sync or these video lines will shift.
739 
740 
741 Capture Feature Selection Controls
742 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
743 
744 These controls are all specific to video capture.
745 
746 - Sensor Flipped Horizontally:
747 
748         the image is flipped horizontally and the
749         V4L2_IN_ST_HFLIP input status flag is set. This emulates the case where
750         a sensor is for example mounted upside down.
751 
752 - Sensor Flipped Vertically:
753 
754         the image is flipped vertically and the
755         V4L2_IN_ST_VFLIP input status flag is set. This emulates the case where
756         a sensor is for example mounted upside down.
757 
758 - Standard Aspect Ratio:
759 
760         selects if the image aspect ratio as used for the TV or
761         S-Video input should be 4x3, 16x9 or anamorphic widescreen. This may
762         introduce letterboxing.
763 
764 - DV Timings Aspect Ratio:
765 
766         selects if the image aspect ratio as used for the HDMI
767         input should be the same as the source width and height ratio, or if
768         it should be 4x3 or 16x9. This may introduce letter or pillarboxing.
769 
770 - Timestamp Source:
771 
772         selects when the timestamp for each buffer is taken.
773 
774 - Colorspace:
775 
776         selects which colorspace should be used when generating the image.
777         This only applies if the CSC Colorbar test pattern is selected,
778         otherwise the test pattern will go through unconverted.
779         This behavior is also what you want, since a 75% Colorbar
780         should really have 75% signal intensity and should not be affected
781         by colorspace conversions.
782 
783         Changing the colorspace will result in the V4L2_EVENT_SOURCE_CHANGE
784         to be sent since it emulates a detected colorspace change.
785 
786 - Transfer Function:
787 
788         selects which colorspace transfer function should be used when
789         generating an image. This only applies if the CSC Colorbar test pattern is
790         selected, otherwise the test pattern will go through unconverted.
791         This behavior is also what you want, since a 75% Colorbar
792         should really have 75% signal intensity and should not be affected
793         by colorspace conversions.
794 
795         Changing the transfer function will result in the V4L2_EVENT_SOURCE_CHANGE
796         to be sent since it emulates a detected colorspace change.
797 
798 - Y'CbCr Encoding:
799 
800         selects which Y'CbCr encoding should be used when generating
801         a Y'CbCr image. This only applies if the format is set to a Y'CbCr format
802         as opposed to an RGB format.
803 
804         Changing the Y'CbCr encoding will result in the V4L2_EVENT_SOURCE_CHANGE
805         to be sent since it emulates a detected colorspace change.
806 
807 - Quantization:
808 
809         selects which quantization should be used for the RGB or Y'CbCr
810         encoding when generating the test pattern.
811 
812         Changing the quantization will result in the V4L2_EVENT_SOURCE_CHANGE
813         to be sent since it emulates a detected colorspace change.
814 
815 - Limited RGB Range (16-235):
816 
817         selects if the RGB range of the HDMI source should
818         be limited or full range. This combines with the Digital Video 'Rx RGB
819         Quantization Range' control and can be used to test what happens if
820         a source provides you with the wrong quantization range information.
821         See the description of that control for more details.
822 
823 - Apply Alpha To Red Only:
824 
825         apply the alpha channel as set by the 'Alpha Component'
826         user control to the red color of the test pattern only.
827 
828 - Enable Capture Cropping:
829 
830         enables crop support. This control is only present if
831         the ccs_cap_mode module option is set to the default value of -1 and if
832         the no_error_inj module option is set to 0 (the default).
833 
834 - Enable Capture Composing:
835 
836         enables composing support. This control is only
837         present if the ccs_cap_mode module option is set to the default value of
838         -1 and if the no_error_inj module option is set to 0 (the default).
839 
840 - Enable Capture Scaler:
841 
842         enables support for a scaler (maximum 4 times upscaling
843         and downscaling). This control is only present if the ccs_cap_mode
844         module option is set to the default value of -1 and if the no_error_inj
845         module option is set to 0 (the default).
846 
847 - Maximum EDID Blocks:
848 
849         determines how many EDID blocks the driver supports.
850         Note that the vivid driver does not actually interpret new EDID
851         data, it just stores it. It allows for up to 256 EDID blocks
852         which is the maximum supported by the standard.
853 
854 - Fill Percentage of Frame:
855 
856         can be used to draw only the top X percent
857         of the image. Since each frame has to be drawn by the driver, this
858         demands a lot of the CPU. For large resolutions this becomes
859         problematic. By drawing only part of the image this CPU load can
860         be reduced.
861 
862 
863 Output Feature Selection Controls
864 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
865 
866 These controls are all specific to video output.
867 
868 - Enable Output Cropping:
869 
870         enables crop support. This control is only present if
871         the ccs_out_mode module option is set to the default value of -1 and if
872         the no_error_inj module option is set to 0 (the default).
873 
874 - Enable Output Composing:
875 
876         enables composing support. This control is only
877         present if the ccs_out_mode module option is set to the default value of
878         -1 and if the no_error_inj module option is set to 0 (the default).
879 
880 - Enable Output Scaler:
881 
882         enables support for a scaler (maximum 4 times upscaling
883         and downscaling). This control is only present if the ccs_out_mode
884         module option is set to the default value of -1 and if the no_error_inj
885         module option is set to 0 (the default).
886 
887 
888 Error Injection Controls
889 ^^^^^^^^^^^^^^^^^^^^^^^^
890 
891 The following two controls are only valid for video and vbi capture.
892 
893 - Standard Signal Mode:
894 
895         selects the behavior of VIDIOC_QUERYSTD: what should it return?
896 
897         Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
898         to be sent since it emulates a changed input condition (e.g. a cable
899         was plugged in or out).
900 
901 - Standard:
902 
903         selects the standard that VIDIOC_QUERYSTD should return if the
904         previous control is set to "Selected Standard".
905 
906         Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
907         to be sent since it emulates a changed input standard.
908 
909 
910 The following two controls are only valid for video capture.
911 
912 - DV Timings Signal Mode:
913 
914         selects the behavior of VIDIOC_QUERY_DV_TIMINGS: what
915         should it return?
916 
917         Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
918         to be sent since it emulates a changed input condition (e.g. a cable
919         was plugged in or out).
920 
921 - DV Timings:
922 
923         selects the timings the VIDIOC_QUERY_DV_TIMINGS should return
924         if the previous control is set to "Selected DV Timings".
925 
926         Changing this control will result in the V4L2_EVENT_SOURCE_CHANGE
927         to be sent since it emulates changed input timings.
928 
929 
930 The following controls are only present if the no_error_inj module option
931 is set to 0 (the default). These controls are valid for video and vbi
932 capture and output streams and for the SDR capture device except for the
933 Disconnect control which is valid for all devices.
934 
935 - Wrap Sequence Number:
936 
937         test what happens when you wrap the sequence number in
938         struct v4l2_buffer around.
939 
940 - Wrap Timestamp:
941 
942         test what happens when you wrap the timestamp in struct
943         v4l2_buffer around.
944 
945 - Percentage of Dropped Buffers:
946 
947         sets the percentage of buffers that
948         are never returned by the driver (i.e., they are dropped).
949 
950 - Disconnect:
951 
952         emulates a USB disconnect. The device will act as if it has
953         been disconnected. Only after all open filehandles to the device
954         node have been closed will the device become 'connected' again.
955 
956 - Inject V4L2_BUF_FLAG_ERROR:
957 
958         when pressed, the next frame returned by
959         the driver will have the error flag set (i.e. the frame is marked
960         corrupt).
961 
962 - Inject VIDIOC_REQBUFS Error:
963 
964         when pressed, the next REQBUFS or CREATE_BUFS
965         ioctl call will fail with an error. To be precise: the videobuf2
966         queue_setup() op will return -EINVAL.
967 
968 - Inject VIDIOC_QBUF Error:
969 
970         when pressed, the next VIDIOC_QBUF or
971         VIDIOC_PREPARE_BUFFER ioctl call will fail with an error. To be
972         precise: the videobuf2 buf_prepare() op will return -EINVAL.
973 
974 - Inject VIDIOC_STREAMON Error:
975 
976         when pressed, the next VIDIOC_STREAMON ioctl
977         call will fail with an error. To be precise: the videobuf2
978         start_streaming() op will return -EINVAL.
979 
980 - Inject Fatal Streaming Error:
981 
982         when pressed, the streaming core will be
983         marked as having suffered a fatal error, the only way to recover
984         from that is to stop streaming. To be precise: the videobuf2
985         vb2_queue_error() function is called.
986 
987 
988 VBI Raw Capture Controls
989 ^^^^^^^^^^^^^^^^^^^^^^^^
990 
991 - Interlaced VBI Format:
992 
993         if set, then the raw VBI data will be interlaced instead
994         of providing it grouped by field.
995 
996 
997 Digital Video Controls
998 ~~~~~~~~~~~~~~~~~~~~~~
999 
1000 - Rx RGB Quantization Range:
1001 
1002         sets the RGB quantization detection of the HDMI
1003         input. This combines with the Vivid 'Limited RGB Range (16-235)'
1004         control and can be used to test what happens if a source provides
1005         you with the wrong quantization range information. This can be tested
1006         by selecting an HDMI input, setting this control to Full or Limited
1007         range and selecting the opposite in the 'Limited RGB Range (16-235)'
1008         control. The effect is easy to see if the 'Gray Ramp' test pattern
1009         is selected.
1010 
1011 - Tx RGB Quantization Range:
1012 
1013         sets the RGB quantization detection of the HDMI
1014         output. It is currently not used for anything in vivid, but most HDMI
1015         transmitters would typically have this control.
1016 
1017 - Transmit Mode:
1018 
1019         sets the transmit mode of the HDMI output to HDMI or DVI-D. This
1020         affects the reported colorspace since DVI_D outputs will always use
1021         sRGB.
1022 
1023 
1024 FM Radio Receiver Controls
1025 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1026 
1027 - RDS Reception:
1028 
1029         set if the RDS receiver should be enabled.
1030 
1031 - RDS Program Type:
1032 
1033 
1034 - RDS PS Name:
1035 
1036 
1037 - RDS Radio Text:
1038 
1039 
1040 - RDS Traffic Announcement:
1041 
1042 
1043 - RDS Traffic Program:
1044 
1045 
1046 - RDS Music:
1047 
1048         these are all read-only controls. If RDS Rx I/O Mode is set to
1049         "Block I/O", then they are inactive as well. If RDS Rx I/O Mode is set
1050         to "Controls", then these controls report the received RDS data.
1051 
1052 .. note::
1053         The vivid implementation of this is pretty basic: they are only
1054         updated when you set a new frequency or when you get the tuner status
1055         (VIDIOC_G_TUNER).
1056 
1057 - Radio HW Seek Mode:
1058 
1059         can be one of "Bounded", "Wrap Around" or "Both". This
1060         determines if VIDIOC_S_HW_FREQ_SEEK will be bounded by the frequency
1061         range or wrap-around or if it is selectable by the user.
1062 
1063 - Radio Programmable HW Seek:
1064 
1065         if set, then the user can provide the lower and
1066         upper bound of the HW Seek. Otherwise the frequency range boundaries
1067         will be used.
1068 
1069 - Generate RBDS Instead of RDS:
1070 
1071         if set, then generate RBDS (the US variant of
1072         RDS) data instead of RDS (European-style RDS). This affects only the
1073         PICODE and PTY codes.
1074 
1075 - RDS Rx I/O Mode:
1076 
1077         this can be "Block I/O" where the RDS blocks have to be read()
1078         by the application, or "Controls" where the RDS data is provided by
1079         the RDS controls mentioned above.
1080 
1081 
1082 FM Radio Modulator Controls
1083 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
1084 
1085 - RDS Program ID:
1086 
1087 
1088 - RDS Program Type:
1089 
1090 
1091 - RDS PS Name:
1092 
1093 
1094 - RDS Radio Text:
1095 
1096 
1097 - RDS Stereo:
1098 
1099 
1100 - RDS Artificial Head:
1101 
1102 
1103 - RDS Compressed:
1104 
1105 
1106 - RDS Dynamic PTY:
1107 
1108 
1109 - RDS Traffic Announcement:
1110 
1111 
1112 - RDS Traffic Program:
1113 
1114 
1115 - RDS Music:
1116 
1117         these are all controls that set the RDS data that is transmitted by
1118         the FM modulator.
1119 
1120 - RDS Tx I/O Mode:
1121 
1122         this can be "Block I/O" where the application has to use write()
1123         to pass the RDS blocks to the driver, or "Controls" where the RDS data
1124         is Provided by the RDS controls mentioned above.
1125 
1126 Metadata Capture Controls
1127 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1128 
1129 - Generate PTS
1130 
1131         if set, then the generated metadata stream contains Presentation timestamp.
1132 
1133 - Generate SCR
1134 
1135         if set, then the generated metadata stream contains Source Clock information.
1136 
1137 
1138 Video, Sliced VBI and HDMI CEC Looping
1139 --------------------------------------
1140 
1141 Video Looping functionality is supported for devices created by the same
1142 vivid driver instance, as well as across multiple instances of the vivid driver.
1143 The vivid driver supports looping of video and Sliced VBI data between an S-Video output
1144 and an S-Video input. It also supports looping of video and HDMI CEC data between an
1145 HDMI output and an HDMI input.
1146 
1147 To enable looping, set the 'HDMI/S-Video XXX-N Is Connected To' control(s) to select
1148 whether an input uses the Test Pattern Generator, or is disconnected, or is connected
1149 to an output. An input can be connected to an output from any vivid instance.
1150 The inputs and outputs are numbered XXX-N where XXX is the vivid instance number
1151 (see module option n_devs). If there is only one vivid instance (the default), then
1152 XXX will be 000. And N is the Nth S-Video/HDMI input or output of that instance.
1153 If vivid is loaded without module options, then you can connect the S-Video 000-0 input
1154 to the S-Video 000-0 output, or the HDMI 000-0 input to the HDMI 000-0 output.
1155 This is the equivalent of connecting or disconnecting a cable between an input and an
1156 output in a physical device.
1157 
1158 If an 'HDMI/S-Video XXX-N Is Connected To' control selected an output, then the video
1159 output will be looped to the video input provided that:
1160 
1161 - the currently selected input matches the input indicated by the control name.
1162 
1163 - in the vivid instance of the output connector, the currently selected output matches
1164   the output indicated by the control's value.
1165 
1166 - the video resolution of the video input must match that of the video output.
1167   So it is not possible to loop a 50 Hz (720x576) S-Video output to a 60 Hz
1168   (720x480) S-Video input, or a 720p60 HDMI output to a 1080p30 input.
1169 
1170 - the pixel formats must be identical on both sides. Otherwise the driver would
1171   have to do pixel format conversion as well, and that's taking things too far.
1172 
1173 - the field settings must be identical on both sides. Same reason as above:
1174   requiring the driver to convert from one field format to another complicated
1175   matters too much. This also prohibits capturing with 'Field Top' or 'Field
1176   Bottom' when the output video is set to 'Field Alternate'. This combination,
1177   while legal, became too complicated to support. Both sides have to be 'Field
1178   Alternate' for this to work. Also note that for this specific case the
1179   sequence and field counting in struct v4l2_buffer on the capture side may not
1180   be 100% accurate.
1181 
1182 - field settings V4L2_FIELD_SEQ_TB/BT are not supported. While it is possible to
1183   implement this, it would mean a lot of work to get this right. Since these
1184   field values are rarely used the decision was made not to implement this for
1185   now.
1186 
1187 - on the input side the "Standard Signal Mode" for the S-Video input or the
1188   "DV Timings Signal Mode" for the HDMI input should be configured so that a
1189   valid signal is passed to the video input.
1190 
1191 If any condition is not valid, then the 'Noise' test pattern is shown.
1192 
1193 The framerates do not have to match, although this might change in the future.
1194 
1195 By default you will see the OSD text superimposed on top of the looped video.
1196 This can be turned off by changing the "OSD Text Mode" control of the video
1197 capture device.
1198 
1199 For VBI looping to work all of the above must be valid and in addition the vbi
1200 output must be configured for sliced VBI. The VBI capture side can be configured
1201 for either raw or sliced VBI. Note that at the moment only CC/XDS (60 Hz formats)
1202 and WSS (50 Hz formats) VBI data is looped. Teletext VBI data is not looped.
1203 
1204 
1205 Radio & RDS Looping
1206 -------------------
1207 
1208 The vivid driver supports looping of RDS output to RDS input.
1209 
1210 Since radio is wireless this looping always happens if the radio receiver
1211 frequency is close to the radio transmitter frequency. In that case the radio
1212 transmitter will 'override' the emulated radio stations.
1213 
1214 RDS looping is currently supported only between devices created by the same
1215 vivid driver instance.
1216 
1217 As mentioned in the "Radio Receiver" section, the radio receiver emulates
1218 stations at regular frequency intervals. Depending on the frequency of the
1219 radio receiver a signal strength value is calculated (this is returned by
1220 VIDIOC_G_TUNER). However, it will also look at the frequency set by the radio
1221 transmitter and if that results in a higher signal strength than the settings
1222 of the radio transmitter will be used as if it was a valid station. This also
1223 includes the RDS data (if any) that the transmitter 'transmits'. This is
1224 received faithfully on the receiver side. Note that when the driver is loaded
1225 the frequencies of the radio receiver and transmitter are not identical, so
1226 initially no looping takes place.
1227 
1228 
1229 Cropping, Composing, Scaling
1230 ----------------------------
1231 
1232 This driver supports cropping, composing and scaling in any combination. Normally
1233 which features are supported can be selected through the Vivid controls,
1234 but it is also possible to hardcode it when the module is loaded through the
1235 ccs_cap_mode and ccs_out_mode module options. See "Configuring the driver" on
1236 the details of these module options.
1237 
1238 This allows you to test your application for all these variations.
1239 
1240 Note that the webcam input never supports cropping, composing or scaling. That
1241 only applies to the TV/S-Video/HDMI inputs and outputs. The reason is that
1242 webcams, including this virtual implementation, normally use
1243 VIDIOC_ENUM_FRAMESIZES to list a set of discrete framesizes that it supports.
1244 And that does not combine with cropping, composing or scaling. This is
1245 primarily a limitation of the V4L2 API which is carefully reproduced here.
1246 
1247 The minimum and maximum resolutions that the scaler can achieve are 16x16 and
1248 (4096 * 4) x (2160 x 4), but it can only scale up or down by a factor of 4 or
1249 less. So for a source resolution of 1280x720 the minimum the scaler can do is
1250 320x180 and the maximum is 5120x2880. You can play around with this using the
1251 qv4l2 test tool and you will see these dependencies.
1252 
1253 This driver also supports larger 'bytesperline' settings, something that
1254 VIDIOC_S_FMT allows but that few drivers implement.
1255 
1256 The scaler is a simple scaler that uses the Coarse Bresenham algorithm. It's
1257 designed for speed and simplicity, not quality.
1258 
1259 If the combination of crop, compose and scaling allows it, then it is possible
1260 to change crop and compose rectangles on the fly.
1261 
1262 
1263 Formats
1264 -------
1265 
1266 The driver supports all the regular packed and planar 4:4:4, 4:2:2 and 4:2:0
1267 YUYV formats, 8, 16, 24 and 32 RGB packed formats and various multiplanar
1268 formats.
1269 
1270 The alpha component can be set through the 'Alpha Component' User control
1271 for those formats that support it. If the 'Apply Alpha To Red Only' control
1272 is set, then the alpha component is only used for the color red and set to
1273 0 otherwise.
1274 
1275 The driver has to be configured to support the multiplanar formats. By default
1276 the driver instances are single-planar. This can be changed by setting the
1277 multiplanar module option, see "Configuring the driver" for more details on that
1278 option.
1279 
1280 If the driver instance is using the multiplanar formats/API, then the first
1281 single planar format (YUYV) and the multiplanar NV16M and NV61M formats the
1282 will have a plane that has a non-zero data_offset of 128 bytes. It is rare for
1283 data_offset to be non-zero, so this is a useful feature for testing applications.
1284 
1285 Video output will also honor any data_offset that the application set.
1286 
1287 
1288 Output Overlay
1289 --------------
1290 
1291 Note: output overlays are primarily implemented in order to test the existing
1292 V4L2 output overlay API. Whether this API should be used for new drivers is
1293 questionable.
1294 
1295 This driver has support for an output overlay and is capable of:
1296 
1297         - bitmap clipping,
1298         - list clipping (up to 16 rectangles)
1299         - chromakey
1300         - source chromakey
1301         - global alpha
1302         - local alpha
1303         - local inverse alpha
1304 
1305 Output overlays are not supported for multiplanar formats. In addition, the
1306 pixelformat of the capture format and that of the framebuffer must be the
1307 same for the overlay to work. Otherwise VIDIOC_OVERLAY will return an error.
1308 
1309 Output overlays only work if the driver has been configured to create a
1310 framebuffer by setting flag 0x10000 in the node_types module option. The
1311 created framebuffer has a size of 720x576 and supports ARGB 1:5:5:5 and
1312 RGB 5:6:5.
1313 
1314 In order to see the effects of the various clipping, chromakeying or alpha
1315 processing capabilities you need to turn on video looping and see the results
1316 on the capture side. The use of the clipping, chromakeying or alpha processing
1317 capabilities will slow down the video loop considerably as a lot of checks have
1318 to be done per pixel.
1319 
1320 
1321 CEC (Consumer Electronics Control)
1322 ----------------------------------
1323 
1324 If there are HDMI inputs then a CEC adapter will be created that has
1325 the same number of input ports. This is the equivalent of e.g. a TV that
1326 has that number of inputs. Each HDMI output will also create a
1327 CEC adapter that is hooked up to the corresponding input port, or (if there
1328 are more outputs than inputs) is not hooked up at all. In other words,
1329 this is the equivalent of hooking up each output device to an input port of
1330 the TV. Any remaining output devices remain unconnected.
1331 
1332 The EDID that each output reads reports a unique CEC physical address that is
1333 based on the physical address of the EDID of the input. So if the EDID of the
1334 receiver has physical address A.B.0.0, then each output will see an EDID
1335 containing physical address A.B.C.0 where C is 1 to the number of inputs. If
1336 there are more outputs than inputs then the remaining outputs have a CEC adapter
1337 that is disabled and reports an invalid physical address.
1338 
1339 
1340 Some Future Improvements
1341 ------------------------
1342 
1343 Just as a reminder and in no particular order:
1344 
1345 - Add a virtual alsa driver to test audio
1346 - Add virtual sub-devices
1347 - Some support for testing compressed video
1348 - Add support to loop raw VBI output to raw VBI input
1349 - Add support to loop teletext sliced VBI output to VBI input
1350 - Fix sequence/field numbering when looping of video with alternate fields
1351 - Add support for V4L2_CID_BG_COLOR for video outputs
1352 - Add ARGB888 overlay support: better testing of the alpha channel
1353 - Improve pixel aspect support in the tpg code by passing a real v4l2_fract
1354 - Use per-queue locks and/or per-device locks to improve throughput
1355 - The SDR radio should use the same 'frequencies' for stations as the normal
1356   radio receiver, and give back noise if the frequency doesn't match up with
1357   a station frequency
1358 - Make a thread for the RDS generation, that would help in particular for the
1359   "Controls" RDS Rx I/O Mode as the read-only RDS controls could be updated
1360   in real-time.
1361 - Changing the EDID doesn't wait 100 ms before setting the HPD signal.

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