1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 .. c:namespace:: V4L 2 .. c:namespace:: V4L 3 3 4 .. _VIDIOC_G_DV_TIMINGS: 4 .. _VIDIOC_G_DV_TIMINGS: 5 5 6 ********************************************** 6 ********************************************** 7 ioctl VIDIOC_G_DV_TIMINGS, VIDIOC_S_DV_TIMINGS 7 ioctl VIDIOC_G_DV_TIMINGS, VIDIOC_S_DV_TIMINGS 8 ********************************************** 8 ********************************************** 9 9 10 Name 10 Name 11 ==== 11 ==== 12 12 13 VIDIOC_G_DV_TIMINGS - VIDIOC_S_DV_TIMINGS - VI 13 VIDIOC_G_DV_TIMINGS - VIDIOC_S_DV_TIMINGS - VIDIOC_SUBDEV_G_DV_TIMINGS - VIDIOC_SUBDEV_S_DV_TIMINGS - Get or set DV timings for input or output 14 14 15 Synopsis 15 Synopsis 16 ======== 16 ======== 17 17 18 .. c:macro:: VIDIOC_G_DV_TIMINGS 18 .. c:macro:: VIDIOC_G_DV_TIMINGS 19 19 20 ``int ioctl(int fd, VIDIOC_G_DV_TIMINGS, struc 20 ``int ioctl(int fd, VIDIOC_G_DV_TIMINGS, struct v4l2_dv_timings *argp)`` 21 21 22 .. c:macro:: VIDIOC_S_DV_TIMINGS 22 .. c:macro:: VIDIOC_S_DV_TIMINGS 23 23 24 ``int ioctl(int fd, VIDIOC_S_DV_TIMINGS, struc 24 ``int ioctl(int fd, VIDIOC_S_DV_TIMINGS, struct v4l2_dv_timings *argp)`` 25 25 26 .. c:macro:: VIDIOC_SUBDEV_G_DV_TIMINGS 26 .. c:macro:: VIDIOC_SUBDEV_G_DV_TIMINGS 27 27 28 ``int ioctl(int fd, VIDIOC_SUBDEV_G_DV_TIMINGS 28 ``int ioctl(int fd, VIDIOC_SUBDEV_G_DV_TIMINGS, struct v4l2_dv_timings *argp)`` 29 29 30 .. c:macro:: VIDIOC_SUBDEV_S_DV_TIMINGS 30 .. c:macro:: VIDIOC_SUBDEV_S_DV_TIMINGS 31 31 32 ``int ioctl(int fd, VIDIOC_SUBDEV_S_DV_TIMINGS 32 ``int ioctl(int fd, VIDIOC_SUBDEV_S_DV_TIMINGS, struct v4l2_dv_timings *argp)`` 33 33 34 Arguments 34 Arguments 35 ========= 35 ========= 36 36 37 ``fd`` 37 ``fd`` 38 File descriptor returned by :c:func:`open( 38 File descriptor returned by :c:func:`open()`. 39 39 40 ``argp`` 40 ``argp`` 41 Pointer to struct :c:type:`v4l2_dv_timings 41 Pointer to struct :c:type:`v4l2_dv_timings`. 42 42 43 Description 43 Description 44 =========== 44 =========== 45 45 46 To set DV timings for the input or output, app 46 To set DV timings for the input or output, applications use the 47 :ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS 47 :ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl and to get the current timings, 48 applications use the :ref:`VIDIOC_G_DV_TIMINGS 48 applications use the :ref:`VIDIOC_G_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` ioctl. The detailed timing 49 information is filled in using the structure s 49 information is filled in using the structure struct 50 :c:type:`v4l2_dv_timings`. These ioctls take a 50 :c:type:`v4l2_dv_timings`. These ioctls take a 51 pointer to the struct :c:type:`v4l2_dv_timings 51 pointer to the struct :c:type:`v4l2_dv_timings` 52 structure as argument. If the ioctl is not sup 52 structure as argument. If the ioctl is not supported or the timing 53 values are not correct, the driver returns ``E 53 values are not correct, the driver returns ``EINVAL`` error code. 54 54 55 Calling ``VIDIOC_SUBDEV_S_DV_TIMINGS`` on a su 55 Calling ``VIDIOC_SUBDEV_S_DV_TIMINGS`` on a subdev device node that has been 56 registered in read-only mode is not allowed. A 56 registered in read-only mode is not allowed. An error is returned and the errno 57 variable is set to ``-EPERM``. 57 variable is set to ``-EPERM``. 58 58 59 The ``linux/v4l2-dv-timings.h`` header can be 59 The ``linux/v4l2-dv-timings.h`` header can be used to get the timings of 60 the formats in the :ref:`cea861` and :ref:`ves 60 the formats in the :ref:`cea861` and :ref:`vesadmt` standards. If 61 the current input or output does not support D 61 the current input or output does not support DV timings (e.g. if 62 :ref:`VIDIOC_ENUMINPUT` does not set the 62 :ref:`VIDIOC_ENUMINPUT` does not set the 63 ``V4L2_IN_CAP_DV_TIMINGS`` flag), then ``ENODA 63 ``V4L2_IN_CAP_DV_TIMINGS`` flag), then ``ENODATA`` error code is returned. 64 64 65 Return Value 65 Return Value 66 ============ 66 ============ 67 67 68 On success 0 is returned, on error -1 and the 68 On success 0 is returned, on error -1 and the ``errno`` variable is set 69 appropriately. The generic error codes are des 69 appropriately. The generic error codes are described at the 70 :ref:`Generic Error Codes <gen-errors>` chapte 70 :ref:`Generic Error Codes <gen-errors>` chapter. 71 71 72 EINVAL 72 EINVAL 73 This ioctl is not supported, or the :ref:` 73 This ioctl is not supported, or the :ref:`VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>` 74 parameter was unsuitable. 74 parameter was unsuitable. 75 75 76 ENODATA 76 ENODATA 77 Digital video timings are not supported fo 77 Digital video timings are not supported for this input or output. 78 78 79 EBUSY 79 EBUSY 80 The device is busy and therefore can not c 80 The device is busy and therefore can not change the timings. 81 81 82 EPERM 82 EPERM 83 ``VIDIOC_SUBDEV_S_DV_TIMINGS`` has been ca 83 ``VIDIOC_SUBDEV_S_DV_TIMINGS`` has been called on a read-only subdevice. 84 84 85 .. c:type:: v4l2_bt_timings !! 85 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 86 << 87 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm << 88 86 89 .. cssclass:: longtable !! 87 .. c:type:: v4l2_bt_timings 90 88 91 .. flat-table:: struct v4l2_bt_timings 89 .. flat-table:: struct v4l2_bt_timings 92 :header-rows: 0 90 :header-rows: 0 93 :stub-columns: 0 91 :stub-columns: 0 94 :widths: 1 1 2 92 :widths: 1 1 2 95 93 96 * - __u32 94 * - __u32 97 - ``width`` 95 - ``width`` 98 - Width of the active video in pixels. 96 - Width of the active video in pixels. 99 * - __u32 97 * - __u32 100 - ``height`` 98 - ``height`` 101 - Height of the active video frame in li 99 - Height of the active video frame in lines. So for interlaced 102 formats the height of the active video 100 formats the height of the active video in each field is 103 ``height``/2. 101 ``height``/2. 104 * - __u32 102 * - __u32 105 - ``interlaced`` 103 - ``interlaced`` 106 - Progressive (``V4L2_DV_PROGRESSIVE``) 104 - Progressive (``V4L2_DV_PROGRESSIVE``) or interlaced (``V4L2_DV_INTERLACED``). 107 * - __u32 105 * - __u32 108 - ``polarities`` 106 - ``polarities`` 109 - This is a bit mask that defines polari 107 - This is a bit mask that defines polarities of sync signals. bit 0 110 (``V4L2_DV_VSYNC_POS_POL``) is for ver 108 (``V4L2_DV_VSYNC_POS_POL``) is for vertical sync polarity and bit 111 1 (``V4L2_DV_HSYNC_POS_POL``) is for h 109 1 (``V4L2_DV_HSYNC_POS_POL``) is for horizontal sync polarity. If 112 the bit is set (1) it is positive pola 110 the bit is set (1) it is positive polarity and if is cleared (0), 113 it is negative polarity. 111 it is negative polarity. 114 * - __u64 112 * - __u64 115 - ``pixelclock`` 113 - ``pixelclock`` 116 - Pixel clock in Hz. Ex. 74.25MHz->74250 114 - Pixel clock in Hz. Ex. 74.25MHz->74250000 117 * - __u32 115 * - __u32 118 - ``hfrontporch`` 116 - ``hfrontporch`` 119 - Horizontal front porch in pixels 117 - Horizontal front porch in pixels 120 * - __u32 118 * - __u32 121 - ``hsync`` 119 - ``hsync`` 122 - Horizontal sync length in pixels 120 - Horizontal sync length in pixels 123 * - __u32 121 * - __u32 124 - ``hbackporch`` 122 - ``hbackporch`` 125 - Horizontal back porch in pixels 123 - Horizontal back porch in pixels 126 * - __u32 124 * - __u32 127 - ``vfrontporch`` 125 - ``vfrontporch`` 128 - Vertical front porch in lines. For int 126 - Vertical front porch in lines. For interlaced formats this refers 129 to the odd field (aka field 1). 127 to the odd field (aka field 1). 130 * - __u32 128 * - __u32 131 - ``vsync`` 129 - ``vsync`` 132 - Vertical sync length in lines. For int 130 - Vertical sync length in lines. For interlaced formats this refers 133 to the odd field (aka field 1). 131 to the odd field (aka field 1). 134 * - __u32 132 * - __u32 135 - ``vbackporch`` 133 - ``vbackporch`` 136 - Vertical back porch in lines. For inte 134 - Vertical back porch in lines. For interlaced formats this refers 137 to the odd field (aka field 1). 135 to the odd field (aka field 1). 138 * - __u32 136 * - __u32 139 - ``il_vfrontporch`` 137 - ``il_vfrontporch`` 140 - Vertical front porch in lines for the 138 - Vertical front porch in lines for the even field (aka field 2) of 141 interlaced field formats. Must be 0 fo 139 interlaced field formats. Must be 0 for progressive formats. 142 * - __u32 140 * - __u32 143 - ``il_vsync`` 141 - ``il_vsync`` 144 - Vertical sync length in lines for the 142 - Vertical sync length in lines for the even field (aka field 2) of 145 interlaced field formats. Must be 0 fo 143 interlaced field formats. Must be 0 for progressive formats. 146 * - __u32 144 * - __u32 147 - ``il_vbackporch`` 145 - ``il_vbackporch`` 148 - Vertical back porch in lines for the e 146 - Vertical back porch in lines for the even field (aka field 2) of 149 interlaced field formats. Must be 0 fo 147 interlaced field formats. Must be 0 for progressive formats. 150 * - __u32 148 * - __u32 151 - ``standards`` 149 - ``standards`` 152 - The video standard(s) this format belo 150 - The video standard(s) this format belongs to. This will be filled 153 in by the driver. Applications must se 151 in by the driver. Applications must set this to 0. See 154 :ref:`dv-bt-standards` for a list of s 152 :ref:`dv-bt-standards` for a list of standards. 155 * - __u32 153 * - __u32 156 - ``flags`` 154 - ``flags`` 157 - Several flags giving more information 155 - Several flags giving more information about the format. See 158 :ref:`dv-bt-flags` for a description o 156 :ref:`dv-bt-flags` for a description of the flags. 159 * - struct :c:type:`v4l2_fract` 157 * - struct :c:type:`v4l2_fract` 160 - ``picture_aspect`` 158 - ``picture_aspect`` 161 - The picture aspect if the pixels are n 159 - The picture aspect if the pixels are not square. Only valid if the 162 ``V4L2_DV_FL_HAS_PICTURE_ASPECT`` flag 160 ``V4L2_DV_FL_HAS_PICTURE_ASPECT`` flag is set. 163 * - __u8 161 * - __u8 164 - ``cea861_vic`` 162 - ``cea861_vic`` 165 - The Video Identification Code accordin 163 - The Video Identification Code according to the CEA-861 standard. 166 Only valid if the ``V4L2_DV_FL_HAS_CEA 164 Only valid if the ``V4L2_DV_FL_HAS_CEA861_VIC`` flag is set. 167 * - __u8 165 * - __u8 168 - ``hdmi_vic`` 166 - ``hdmi_vic`` 169 - The Video Identification Code accordin 167 - The Video Identification Code according to the HDMI standard. 170 Only valid if the ``V4L2_DV_FL_HAS_HDM 168 Only valid if the ``V4L2_DV_FL_HAS_HDMI_VIC`` flag is set. 171 * - __u8 169 * - __u8 172 - ``reserved[46]`` 170 - ``reserved[46]`` 173 - Reserved for future extensions. Driver 171 - Reserved for future extensions. Drivers and applications must set 174 the array to zero. 172 the array to zero. 175 173 176 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{7.0cm !! 174 .. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{7.0cm}|p{3.5cm}| 177 175 178 .. c:type:: v4l2_dv_timings 176 .. c:type:: v4l2_dv_timings 179 177 180 .. flat-table:: struct v4l2_dv_timings 178 .. flat-table:: struct v4l2_dv_timings 181 :header-rows: 0 179 :header-rows: 0 182 :stub-columns: 0 180 :stub-columns: 0 183 :widths: 1 1 2 181 :widths: 1 1 2 184 182 185 * - __u32 183 * - __u32 186 - ``type`` 184 - ``type`` 187 - Type of DV timings as listed in :ref:` 185 - Type of DV timings as listed in :ref:`dv-timing-types`. 188 * - union { 186 * - union { 189 - (anonymous) 187 - (anonymous) 190 * - struct :c:type:`v4l2_bt_timings` 188 * - struct :c:type:`v4l2_bt_timings` 191 - ``bt`` 189 - ``bt`` 192 - Timings defined by BT.656/1120 specifi 190 - Timings defined by BT.656/1120 specifications 193 * - __u32 191 * - __u32 194 - ``reserved``\ [32] 192 - ``reserved``\ [32] 195 - 193 - 196 * - } 194 * - } 197 - 195 - 198 196 199 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm !! 197 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| 200 198 201 .. _dv-timing-types: 199 .. _dv-timing-types: 202 200 203 .. flat-table:: DV Timing types 201 .. flat-table:: DV Timing types 204 :header-rows: 0 202 :header-rows: 0 205 :stub-columns: 0 203 :stub-columns: 0 206 :widths: 1 1 2 204 :widths: 1 1 2 207 205 208 * - Timing type 206 * - Timing type 209 - value 207 - value 210 - Description 208 - Description 211 * - 209 * - 212 - 210 - 213 - 211 - 214 * - ``V4L2_DV_BT_656_1120`` 212 * - ``V4L2_DV_BT_656_1120`` 215 - 0 213 - 0 216 - BT.656/1120 timings 214 - BT.656/1120 timings 217 215 218 .. tabularcolumns:: |p{6.5cm}|p{11.0cm}| !! 216 .. tabularcolumns:: |p{4.5cm}|p{12.8cm}| 219 << 220 .. cssclass:: longtable << 221 217 222 .. _dv-bt-standards: 218 .. _dv-bt-standards: 223 219 224 .. flat-table:: DV BT Timing standards 220 .. flat-table:: DV BT Timing standards 225 :header-rows: 0 221 :header-rows: 0 226 :stub-columns: 0 222 :stub-columns: 0 227 223 228 * - Timing standard 224 * - Timing standard 229 - Description 225 - Description 230 * - ``V4L2_DV_BT_STD_CEA861`` 226 * - ``V4L2_DV_BT_STD_CEA861`` 231 - The timings follow the CEA-861 Digital 227 - The timings follow the CEA-861 Digital TV Profile standard 232 * - ``V4L2_DV_BT_STD_DMT`` 228 * - ``V4L2_DV_BT_STD_DMT`` 233 - The timings follow the VESA Discrete M 229 - The timings follow the VESA Discrete Monitor Timings standard 234 * - ``V4L2_DV_BT_STD_CVT`` 230 * - ``V4L2_DV_BT_STD_CVT`` 235 - The timings follow the VESA Coordinate 231 - The timings follow the VESA Coordinated Video Timings standard 236 * - ``V4L2_DV_BT_STD_GTF`` 232 * - ``V4L2_DV_BT_STD_GTF`` 237 - The timings follow the VESA Generalize 233 - The timings follow the VESA Generalized Timings Formula standard 238 * - ``V4L2_DV_BT_STD_SDI`` 234 * - ``V4L2_DV_BT_STD_SDI`` 239 - The timings follow the SDI Timings sta 235 - The timings follow the SDI Timings standard. 240 There are no horizontal syncs/porches 236 There are no horizontal syncs/porches at all in this format. 241 Total blanking timings must be set in 237 Total blanking timings must be set in hsync or vsync fields only. 242 238 243 .. tabularcolumns:: |p{7.7cm}|p{9.8cm}| !! 239 .. tabularcolumns:: |p{7.0cm}|p{10.5cm}| 244 << 245 .. cssclass:: longtable << 246 240 247 .. _dv-bt-flags: 241 .. _dv-bt-flags: 248 242 249 .. flat-table:: DV BT Timing flags 243 .. flat-table:: DV BT Timing flags 250 :header-rows: 0 244 :header-rows: 0 251 :stub-columns: 0 245 :stub-columns: 0 252 246 253 * - Flag 247 * - Flag 254 - Description 248 - Description 255 * - ``V4L2_DV_FL_REDUCED_BLANKING`` 249 * - ``V4L2_DV_FL_REDUCED_BLANKING`` 256 - CVT/GTF specific: the timings use redu 250 - CVT/GTF specific: the timings use reduced blanking (CVT) or the 257 'Secondary GTF' curve (GTF). In both c 251 'Secondary GTF' curve (GTF). In both cases the horizontal and/or 258 vertical blanking intervals are reduce 252 vertical blanking intervals are reduced, allowing a higher 259 resolution over the same bandwidth. Th 253 resolution over the same bandwidth. This is a read-only flag, 260 applications must not set this. 254 applications must not set this. 261 * - ``V4L2_DV_FL_CAN_REDUCE_FPS`` 255 * - ``V4L2_DV_FL_CAN_REDUCE_FPS`` 262 - CEA-861 specific: set for CEA-861 form 256 - CEA-861 specific: set for CEA-861 formats with a framerate that is 263 a multiple of six. These formats can b 257 a multiple of six. These formats can be optionally played at 1 / 264 1.001 speed to be compatible with 60 H 258 1.001 speed to be compatible with 60 Hz based standards such as 265 NTSC and PAL-M that use a framerate of 259 NTSC and PAL-M that use a framerate of 29.97 frames per second. If 266 the transmitter can't generate such fr 260 the transmitter can't generate such frequencies, then the flag 267 will also be cleared. This is a read-o 261 will also be cleared. This is a read-only flag, applications must 268 not set this. 262 not set this. 269 * - ``V4L2_DV_FL_REDUCED_FPS`` 263 * - ``V4L2_DV_FL_REDUCED_FPS`` 270 - CEA-861 specific: only valid for video 264 - CEA-861 specific: only valid for video transmitters or video 271 receivers that have the ``V4L2_DV_FL_C 265 receivers that have the ``V4L2_DV_FL_CAN_DETECT_REDUCED_FPS`` 272 set. This flag is cleared otherwise. I 266 set. This flag is cleared otherwise. It is also only valid for 273 formats with the ``V4L2_DV_FL_CAN_REDU 267 formats with the ``V4L2_DV_FL_CAN_REDUCE_FPS`` flag set, for other 274 formats the flag will be cleared by th 268 formats the flag will be cleared by the driver. 275 269 276 If the application sets this flag for 270 If the application sets this flag for a transmitter, then the 277 pixelclock used to set up the transmit 271 pixelclock used to set up the transmitter is divided by 1.001 to 278 make it compatible with NTSC framerate 272 make it compatible with NTSC framerates. If the transmitter can't 279 generate such frequencies, then the fl 273 generate such frequencies, then the flag will be cleared. 280 274 281 If a video receiver detects that the f 275 If a video receiver detects that the format uses a reduced framerate, 282 then it will set this flag to signal t 276 then it will set this flag to signal this to the application. 283 * - ``V4L2_DV_FL_HALF_LINE`` 277 * - ``V4L2_DV_FL_HALF_LINE`` 284 - Specific to interlaced formats: if set 278 - Specific to interlaced formats: if set, then the vertical 285 frontporch of field 1 (aka the odd fie 279 frontporch of field 1 (aka the odd field) is really one half-line 286 longer and the vertical backporch of f 280 longer and the vertical backporch of field 2 (aka the even field) 287 is really one half-line shorter, so ea 281 is really one half-line shorter, so each field has exactly the 288 same number of half-lines. Whether hal 282 same number of half-lines. Whether half-lines can be detected or 289 used depends on the hardware. 283 used depends on the hardware. 290 * - ``V4L2_DV_FL_IS_CE_VIDEO`` 284 * - ``V4L2_DV_FL_IS_CE_VIDEO`` 291 - If set, then this is a Consumer Electr 285 - If set, then this is a Consumer Electronics (CE) video format. 292 Such formats differ from other formats 286 Such formats differ from other formats (commonly called IT 293 formats) in that if R'G'B' encoding is 287 formats) in that if R'G'B' encoding is used then by default the 294 R'G'B' values use limited range (i.e. 288 R'G'B' values use limited range (i.e. 16-235) as opposed to full 295 range (i.e. 0-255). All formats define 289 range (i.e. 0-255). All formats defined in CEA-861 except for the 296 640x480p59.94 format are CE formats. 290 640x480p59.94 format are CE formats. 297 * - ``V4L2_DV_FL_FIRST_FIELD_EXTRA_LINE`` 291 * - ``V4L2_DV_FL_FIRST_FIELD_EXTRA_LINE`` 298 - Some formats like SMPTE-125M have an i 292 - Some formats like SMPTE-125M have an interlaced signal with a odd 299 total height. For these formats, if th 293 total height. For these formats, if this flag is set, the first 300 field has the extra line. Else, it is 294 field has the extra line. Else, it is the second field. 301 * - ``V4L2_DV_FL_HAS_PICTURE_ASPECT`` 295 * - ``V4L2_DV_FL_HAS_PICTURE_ASPECT`` 302 - If set, then the picture_aspect field 296 - If set, then the picture_aspect field is valid. Otherwise assume that 303 the pixels are square, so the picture 297 the pixels are square, so the picture aspect ratio is the same as the 304 width to height ratio. 298 width to height ratio. 305 * - ``V4L2_DV_FL_HAS_CEA861_VIC`` 299 * - ``V4L2_DV_FL_HAS_CEA861_VIC`` 306 - If set, then the cea861_vic field is v 300 - If set, then the cea861_vic field is valid and contains the Video 307 Identification Code as per the CEA-861 301 Identification Code as per the CEA-861 standard. 308 * - ``V4L2_DV_FL_HAS_HDMI_VIC`` 302 * - ``V4L2_DV_FL_HAS_HDMI_VIC`` 309 - If set, then the hdmi_vic field is val 303 - If set, then the hdmi_vic field is valid and contains the Video 310 Identification Code as per the HDMI st 304 Identification Code as per the HDMI standard (HDMI Vendor Specific 311 InfoFrame). 305 InfoFrame). 312 * - ``V4L2_DV_FL_CAN_DETECT_REDUCED_FPS`` 306 * - ``V4L2_DV_FL_CAN_DETECT_REDUCED_FPS`` 313 - CEA-861 specific: only valid for video 307 - CEA-861 specific: only valid for video receivers, the flag is 314 cleared by transmitters. 308 cleared by transmitters. 315 If set, then the hardware can detect t 309 If set, then the hardware can detect the difference between 316 regular framerates and framerates redu 310 regular framerates and framerates reduced by 1000/1001. E.g.: 317 60 vs 59.94 Hz, 30 vs 29.97 Hz or 24 v 311 60 vs 59.94 Hz, 30 vs 29.97 Hz or 24 vs 23.976 Hz.
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