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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_G_ENC_INDEX: |
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4 | |
5 | ************************ | |
6 | ioctl VIDIOC_G_ENC_INDEX | |
7 | ************************ | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_G_ENC_INDEX, struct v4l2_enc_idx *argp ) |
19 | :name: VIDIOC_G_ENC_INDEX | |
5377d91f | 20 | |
586027ce | 21 | |
15e7d615 | 22 | Arguments |
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23 | ========= |
24 | ||
25 | ``fd`` | |
26 | File descriptor returned by :ref:`open() <func-open>`. | |
27 | ||
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28 | ``argp`` |
29 | ||
30 | ||
15e7d615 | 31 | Description |
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32 | =========== |
33 | ||
4e03cb76 | 34 | The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed |
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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 | ||
4e03cb76 | 39 | To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a |
e8be7e97 | 40 | pointer to a struct :c:type:`v4l2_enc_idx`. On success |
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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 | |
4e03cb76 | 46 | picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to |
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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 | ||
ef76c068 | 58 | .. tabularcolumns:: |p{3.5cm}|p{5.6cm}|p{8.4cm}| |
5bd4bb78 | 59 | |
e8be7e97 | 60 | .. c:type:: v4l2_enc_idx |
fa92b04d | 61 | |
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62 | .. flat-table:: struct v4l2_enc_idx |
63 | :header-rows: 0 | |
64 | :stub-columns: 0 | |
ef76c068 | 65 | :widths: 1 3 8 |
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66 | |
67 | ||
68 | - .. row 1 | |
69 | ||
70 | - __u32 | |
71 | ||
72 | - ``entries`` | |
73 | ||
74 | - The number of entries the driver stored in the ``entry`` array. | |
75 | ||
76 | - .. row 2 | |
77 | ||
78 | - __u32 | |
79 | ||
80 | - ``entries_cap`` | |
81 | ||
82 | - The number of entries the driver can buffer. Must be greater than | |
0579e6e3 | 83 | zero. |
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84 | |
85 | - .. row 3 | |
86 | ||
87 | - __u32 | |
88 | ||
8968da9b | 89 | - ``reserved``\ [4] |
5377d91f | 90 | |
ef76c068 | 91 | - Reserved for future extensions. Drivers must set the |
0579e6e3 | 92 | array to zero. |
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93 | |
94 | - .. row 4 | |
95 | ||
e8be7e97 | 96 | - struct :c:type:`v4l2_enc_idx_entry` |
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97 | |
98 | - ``entry``\ [``V4L2_ENC_IDX_ENTRIES``] | |
99 | ||
100 | - Meta data about a compressed video stream. Each element of the | |
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101 | array corresponds to one picture, sorted in ascending order by |
102 | their ``offset``. | |
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103 | |
104 | ||
105 | ||
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106 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
107 | ||
e8be7e97 | 108 | .. c:type:: v4l2_enc_idx_entry |
fa92b04d | 109 | |
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110 | .. flat-table:: struct v4l2_enc_idx_entry |
111 | :header-rows: 0 | |
112 | :stub-columns: 0 | |
113 | :widths: 1 1 2 | |
114 | ||
115 | ||
116 | - .. row 1 | |
117 | ||
118 | - __u64 | |
119 | ||
120 | - ``offset`` | |
121 | ||
122 | - The offset in bytes from the beginning of the compressed video | |
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123 | stream to the beginning of this picture, that is a *PES packet |
124 | header* as defined in :ref:`mpeg2part1` or a *picture header* as | |
125 | defined in :ref:`mpeg2part2`. When the encoder is stopped, the | |
126 | driver resets the offset to zero. | |
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127 | |
128 | - .. row 2 | |
129 | ||
130 | - __u64 | |
131 | ||
132 | - ``pts`` | |
133 | ||
134 | - The 33 bit *Presentation Time Stamp* of this picture as defined in | |
0579e6e3 | 135 | :ref:`mpeg2part1`. |
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136 | |
137 | - .. row 3 | |
138 | ||
139 | - __u32 | |
140 | ||
141 | - ``length`` | |
142 | ||
143 | - The length of this picture in bytes. | |
144 | ||
145 | - .. row 4 | |
146 | ||
147 | - __u32 | |
148 | ||
149 | - ``flags`` | |
150 | ||
151 | - Flags containing the coding type of this picture, see | |
0579e6e3 | 152 | :ref:`enc-idx-flags`. |
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153 | |
154 | - .. row 5 | |
155 | ||
156 | - __u32 | |
157 | ||
8968da9b | 158 | - ``reserved``\ [2] |
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159 | |
160 | - Reserved for future extensions. Drivers must set the array to | |
0579e6e3 | 161 | zero. |
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162 | |
163 | ||
fa92b04d | 164 | .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| |
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165 | |
166 | .. _enc-idx-flags: | |
167 | ||
168 | .. flat-table:: Index Entry Flags | |
169 | :header-rows: 0 | |
170 | :stub-columns: 0 | |
171 | :widths: 3 1 4 | |
172 | ||
173 | ||
174 | - .. row 1 | |
175 | ||
176 | - ``V4L2_ENC_IDX_FRAME_I`` | |
177 | ||
178 | - 0x00 | |
179 | ||
180 | - This is an Intra-coded picture. | |
181 | ||
182 | - .. row 2 | |
183 | ||
184 | - ``V4L2_ENC_IDX_FRAME_P`` | |
185 | ||
186 | - 0x01 | |
187 | ||
188 | - This is a Predictive-coded picture. | |
189 | ||
190 | - .. row 3 | |
191 | ||
192 | - ``V4L2_ENC_IDX_FRAME_B`` | |
193 | ||
194 | - 0x02 | |
195 | ||
196 | - This is a Bidirectionally predictive-coded picture. | |
197 | ||
198 | - .. row 4 | |
199 | ||
200 | - ``V4L2_ENC_IDX_FRAME_MASK`` | |
201 | ||
202 | - 0x0F | |
203 | ||
204 | - *AND* the flags field with this mask to obtain the picture coding | |
0579e6e3 | 205 | type. |
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206 | |
207 | ||
15e7d615 | 208 | Return Value |
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209 | ============ |
210 | ||
211 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
212 | appropriately. The generic error codes are described at the | |
213 | :ref:`Generic Error Codes <gen-errors>` chapter. |