1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_ENC_INDEX:
5
6 ************************
7 ioctl VIDIOC_G_ENC_INDEX
8 ************************
9
10 Name
11 ====
12
13 VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_G_ENC_INDEX
19
20 ``int ioctl(int fd, VIDIOC_G_ENC_INDEX, struct v4l2_enc_idx *argp)``
21
22 Arguments
23 =========
24
25 ``fd``
26 File descriptor returned by :c:func:`open()`.
27
28 ``argp``
29 Pointer to struct :c:type:`v4l2_enc_idx`.
30
31 Description
32 ===========
33
34 The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed
35 video stream the same or another application currently reads from the
36 driver, which is useful for random access into the stream without
37 decoding it.
38
39 To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a
40 pointer to a struct :c:type:`v4l2_enc_idx`. On success
41 the driver fills the ``entry`` array, stores the number of elements
42 written in the ``entries`` field, and initializes the ``entries_cap``
43 field.
44
45 Each element of the ``entry`` array contains meta data about one
46 picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to
47 ``V4L2_ENC_IDX_ENTRIES`` entries from a driver buffer, which can hold up
48 to ``entries_cap`` entries. This number can be lower or higher than
49 ``V4L2_ENC_IDX_ENTRIES``, but not zero. When the application fails to
50 read the meta data in time the oldest entries will be lost. When the
51 buffer is empty or no capturing/encoding is in progress, ``entries``
52 will be zero.
53
54 Currently this ioctl is only defined for MPEG-2 program streams and
55 video elementary streams.
56
57 .. tabularcolumns:: |p{4.2cm}|p{6.2cm}|p{6.9cm}|
58
59 .. c:type:: v4l2_enc_idx
60
61 .. flat-table:: struct v4l2_enc_idx
62 :header-rows: 0
63 :stub-columns: 0
64 :widths: 1 3 8
65
66 * - __u32
67 - ``entries``
68 - The number of entries the driver stored in the ``entry`` array.
69 * - __u32
70 - ``entries_cap``
71 - The number of entries the driver can buffer. Must be greater than
72 zero.
73 * - __u32
74 - ``reserved``\ [4]
75 - Reserved for future extensions. Drivers must set the
76 array to zero.
77 * - struct :c:type:`v4l2_enc_idx_entry`
78 - ``entry``\ [``V4L2_ENC_IDX_ENTRIES``]
79 - Meta data about a compressed video stream. Each element of the
80 array corresponds to one picture, sorted in ascending order by
81 their ``offset``.
82
83
84 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
85
86 .. c:type:: v4l2_enc_idx_entry
87
88 .. flat-table:: struct v4l2_enc_idx_entry
89 :header-rows: 0
90 :stub-columns: 0
91 :widths: 1 1 2
92
93 * - __u64
94 - ``offset``
95 - The offset in bytes from the beginning of the compressed video
96 stream to the beginning of this picture, that is a *PES packet
97 header* as defined in :ref:`mpeg2part1` or a *picture header* as
98 defined in :ref:`mpeg2part2`. When the encoder is stopped, the
99 driver resets the offset to zero.
100 * - __u64
101 - ``pts``
102 - The 33 bit *Presentation Time Stamp* of this picture as defined in
103 :ref:`mpeg2part1`.
104 * - __u32
105 - ``length``
106 - The length of this picture in bytes.
107 * - __u32
108 - ``flags``
109 - Flags containing the coding type of this picture, see
110 :ref:`enc-idx-flags`.
111 * - __u32
112 - ``reserved``\ [2]
113 - Reserved for future extensions. Drivers must set the array to
114 zero.
115
116 .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
117
118 .. _enc-idx-flags:
119
120 .. flat-table:: Index Entry Flags
121 :header-rows: 0
122 :stub-columns: 0
123 :widths: 3 1 4
124
125 * - ``V4L2_ENC_IDX_FRAME_I``
126 - 0x00
127 - This is an Intra-coded picture.
128 * - ``V4L2_ENC_IDX_FRAME_P``
129 - 0x01
130 - This is a Predictive-coded picture.
131 * - ``V4L2_ENC_IDX_FRAME_B``
132 - 0x02
133 - This is a Bidirectionally predictive-coded picture.
134 * - ``V4L2_ENC_IDX_FRAME_MASK``
135 - 0x0F
136 - *AND* the flags field with this mask to obtain the picture coding
137 type.
138
139 Return Value
140 ============
141
142 On success 0 is returned, on error -1 and the ``errno`` variable is set
143 appropriately. The generic error codes are described at the
144 :ref:`Generic Error Codes <gen-errors>` chapter.
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