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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 | ||
b7e67f6c | 18 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_enc_idx *argp ) |
5377d91f | 19 | |
586027ce | 20 | |
15e7d615 | 21 | Arguments |
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22 | ========= |
23 | ||
24 | ``fd`` | |
25 | File descriptor returned by :ref:`open() <func-open>`. | |
26 | ||
27 | ``request`` | |
28 | VIDIOC_G_ENC_INDEX | |
29 | ||
30 | ``argp`` | |
31 | ||
32 | ||
15e7d615 | 33 | Description |
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34 | =========== |
35 | ||
4e03cb76 | 36 | The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed |
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37 | video stream the same or another application currently reads from the |
38 | driver, which is useful for random access into the stream without | |
39 | decoding it. | |
40 | ||
4e03cb76 | 41 | To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a |
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42 | pointer to a struct :ref:`v4l2_enc_idx <v4l2-enc-idx>`. On success |
43 | the driver fills the ``entry`` array, stores the number of elements | |
44 | written in the ``entries`` field, and initializes the ``entries_cap`` | |
45 | field. | |
46 | ||
47 | Each element of the ``entry`` array contains meta data about one | |
4e03cb76 | 48 | picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to |
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49 | ``V4L2_ENC_IDX_ENTRIES`` entries from a driver buffer, which can hold up |
50 | to ``entries_cap`` entries. This number can be lower or higher than | |
51 | ``V4L2_ENC_IDX_ENTRIES``, but not zero. When the application fails to | |
52 | read the meta data in time the oldest entries will be lost. When the | |
53 | buffer is empty or no capturing/encoding is in progress, ``entries`` | |
54 | will be zero. | |
55 | ||
56 | Currently this ioctl is only defined for MPEG-2 program streams and | |
57 | video elementary streams. | |
58 | ||
59 | ||
60 | .. _v4l2-enc-idx: | |
61 | ||
62 | .. flat-table:: struct v4l2_enc_idx | |
63 | :header-rows: 0 | |
64 | :stub-columns: 0 | |
65 | :widths: 1 1 2 1 1 | |
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] |
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90 | |
91 | - :cspan:`2` Reserved for future extensions. Drivers must set the | |
0579e6e3 | 92 | array to zero. |
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93 | |
94 | - .. row 4 | |
95 | ||
96 | - struct :ref:`v4l2_enc_idx_entry <v4l2-enc-idx-entry>` | |
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 | ||
106 | .. _v4l2-enc-idx-entry: | |
107 | ||
108 | .. flat-table:: struct v4l2_enc_idx_entry | |
109 | :header-rows: 0 | |
110 | :stub-columns: 0 | |
111 | :widths: 1 1 2 | |
112 | ||
113 | ||
114 | - .. row 1 | |
115 | ||
116 | - __u64 | |
117 | ||
118 | - ``offset`` | |
119 | ||
120 | - The offset in bytes from the beginning of the compressed video | |
0579e6e3 MCC |
121 | stream to the beginning of this picture, that is a *PES packet |
122 | header* as defined in :ref:`mpeg2part1` or a *picture header* as | |
123 | defined in :ref:`mpeg2part2`. When the encoder is stopped, the | |
124 | driver resets the offset to zero. | |
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125 | |
126 | - .. row 2 | |
127 | ||
128 | - __u64 | |
129 | ||
130 | - ``pts`` | |
131 | ||
132 | - The 33 bit *Presentation Time Stamp* of this picture as defined in | |
0579e6e3 | 133 | :ref:`mpeg2part1`. |
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134 | |
135 | - .. row 3 | |
136 | ||
137 | - __u32 | |
138 | ||
139 | - ``length`` | |
140 | ||
141 | - The length of this picture in bytes. | |
142 | ||
143 | - .. row 4 | |
144 | ||
145 | - __u32 | |
146 | ||
147 | - ``flags`` | |
148 | ||
149 | - Flags containing the coding type of this picture, see | |
0579e6e3 | 150 | :ref:`enc-idx-flags`. |
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151 | |
152 | - .. row 5 | |
153 | ||
154 | - __u32 | |
155 | ||
8968da9b | 156 | - ``reserved``\ [2] |
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157 | |
158 | - Reserved for future extensions. Drivers must set the array to | |
0579e6e3 | 159 | zero. |
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160 | |
161 | ||
162 | ||
163 | .. _enc-idx-flags: | |
164 | ||
165 | .. flat-table:: Index Entry Flags | |
166 | :header-rows: 0 | |
167 | :stub-columns: 0 | |
168 | :widths: 3 1 4 | |
169 | ||
170 | ||
171 | - .. row 1 | |
172 | ||
173 | - ``V4L2_ENC_IDX_FRAME_I`` | |
174 | ||
175 | - 0x00 | |
176 | ||
177 | - This is an Intra-coded picture. | |
178 | ||
179 | - .. row 2 | |
180 | ||
181 | - ``V4L2_ENC_IDX_FRAME_P`` | |
182 | ||
183 | - 0x01 | |
184 | ||
185 | - This is a Predictive-coded picture. | |
186 | ||
187 | - .. row 3 | |
188 | ||
189 | - ``V4L2_ENC_IDX_FRAME_B`` | |
190 | ||
191 | - 0x02 | |
192 | ||
193 | - This is a Bidirectionally predictive-coded picture. | |
194 | ||
195 | - .. row 4 | |
196 | ||
197 | - ``V4L2_ENC_IDX_FRAME_MASK`` | |
198 | ||
199 | - 0x0F | |
200 | ||
201 | - *AND* the flags field with this mask to obtain the picture coding | |
0579e6e3 | 202 | type. |
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203 | |
204 | ||
15e7d615 | 205 | Return Value |
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206 | ============ |
207 | ||
208 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
209 | appropriately. The generic error codes are described at the | |
210 | :ref:`Generic Error Codes <gen-errors>` chapter. |