Markus Heiser | 5377d91 | 2016-06-30 15:18:56 +0200 | [diff] [blame] | 1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | |
| 3 | .. _vidioc-g-enc-index: |
| 4 | |
| 5 | ************************ |
| 6 | ioctl VIDIOC_G_ENC_INDEX |
| 7 | ************************ |
| 8 | |
| 9 | *man VIDIOC_G_ENC_INDEX(2)* |
| 10 | |
| 11 | Get meta data about a compressed video stream |
| 12 | |
| 13 | |
| 14 | Synopsis |
| 15 | ======== |
| 16 | |
| 17 | .. c:function:: int ioctl( int fd, int request, struct v4l2_enc_idx *argp ) |
| 18 | |
| 19 | Arguments |
| 20 | ========= |
| 21 | |
| 22 | ``fd`` |
| 23 | File descriptor returned by :ref:`open() <func-open>`. |
| 24 | |
| 25 | ``request`` |
| 26 | VIDIOC_G_ENC_INDEX |
| 27 | |
| 28 | ``argp`` |
| 29 | |
| 30 | |
| 31 | Description |
| 32 | =========== |
| 33 | |
| 34 | The ``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 ``VIDIOC_G_ENC_INDEX`` with a |
| 40 | pointer to a struct :ref:`v4l2_enc_idx <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 ``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 | |
| 58 | .. _v4l2-enc-idx: |
| 59 | |
| 60 | .. flat-table:: struct v4l2_enc_idx |
| 61 | :header-rows: 0 |
| 62 | :stub-columns: 0 |
| 63 | :widths: 1 1 2 1 1 |
| 64 | |
| 65 | |
| 66 | - .. row 1 |
| 67 | |
| 68 | - __u32 |
| 69 | |
| 70 | - ``entries`` |
| 71 | |
| 72 | - The number of entries the driver stored in the ``entry`` array. |
| 73 | |
| 74 | - .. row 2 |
| 75 | |
| 76 | - __u32 |
| 77 | |
| 78 | - ``entries_cap`` |
| 79 | |
| 80 | - The number of entries the driver can buffer. Must be greater than |
| 81 | zero. |
| 82 | |
| 83 | - .. row 3 |
| 84 | |
| 85 | - __u32 |
| 86 | |
| 87 | - ``reserved``\ [4] |
| 88 | |
| 89 | - :cspan:`2` Reserved for future extensions. Drivers must set the |
| 90 | array to zero. |
| 91 | |
| 92 | - .. row 4 |
| 93 | |
| 94 | - struct :ref:`v4l2_enc_idx_entry <v4l2-enc-idx-entry>` |
| 95 | |
| 96 | - ``entry``\ [``V4L2_ENC_IDX_ENTRIES``] |
| 97 | |
| 98 | - Meta data about a compressed video stream. Each element of the |
| 99 | array corresponds to one picture, sorted in ascending order by |
| 100 | their ``offset``. |
| 101 | |
| 102 | |
| 103 | |
| 104 | .. _v4l2-enc-idx-entry: |
| 105 | |
| 106 | .. flat-table:: struct v4l2_enc_idx_entry |
| 107 | :header-rows: 0 |
| 108 | :stub-columns: 0 |
| 109 | :widths: 1 1 2 |
| 110 | |
| 111 | |
| 112 | - .. row 1 |
| 113 | |
| 114 | - __u64 |
| 115 | |
| 116 | - ``offset`` |
| 117 | |
| 118 | - The offset in bytes from the beginning of the compressed video |
| 119 | stream to the beginning of this picture, that is a *PES packet |
| 120 | header* as defined in :ref:`mpeg2part1` or a *picture header* as |
| 121 | defined in :ref:`mpeg2part2`. When the encoder is stopped, the |
| 122 | driver resets the offset to zero. |
| 123 | |
| 124 | - .. row 2 |
| 125 | |
| 126 | - __u64 |
| 127 | |
| 128 | - ``pts`` |
| 129 | |
| 130 | - The 33 bit *Presentation Time Stamp* of this picture as defined in |
| 131 | :ref:`mpeg2part1`. |
| 132 | |
| 133 | - .. row 3 |
| 134 | |
| 135 | - __u32 |
| 136 | |
| 137 | - ``length`` |
| 138 | |
| 139 | - The length of this picture in bytes. |
| 140 | |
| 141 | - .. row 4 |
| 142 | |
| 143 | - __u32 |
| 144 | |
| 145 | - ``flags`` |
| 146 | |
| 147 | - Flags containing the coding type of this picture, see |
| 148 | :ref:`enc-idx-flags`. |
| 149 | |
| 150 | - .. row 5 |
| 151 | |
| 152 | - __u32 |
| 153 | |
| 154 | - ``reserved``\ [2] |
| 155 | |
| 156 | - Reserved for future extensions. Drivers must set the array to |
| 157 | zero. |
| 158 | |
| 159 | |
| 160 | |
| 161 | .. _enc-idx-flags: |
| 162 | |
| 163 | .. flat-table:: Index Entry Flags |
| 164 | :header-rows: 0 |
| 165 | :stub-columns: 0 |
| 166 | :widths: 3 1 4 |
| 167 | |
| 168 | |
| 169 | - .. row 1 |
| 170 | |
| 171 | - ``V4L2_ENC_IDX_FRAME_I`` |
| 172 | |
| 173 | - 0x00 |
| 174 | |
| 175 | - This is an Intra-coded picture. |
| 176 | |
| 177 | - .. row 2 |
| 178 | |
| 179 | - ``V4L2_ENC_IDX_FRAME_P`` |
| 180 | |
| 181 | - 0x01 |
| 182 | |
| 183 | - This is a Predictive-coded picture. |
| 184 | |
| 185 | - .. row 3 |
| 186 | |
| 187 | - ``V4L2_ENC_IDX_FRAME_B`` |
| 188 | |
| 189 | - 0x02 |
| 190 | |
| 191 | - This is a Bidirectionally predictive-coded picture. |
| 192 | |
| 193 | - .. row 4 |
| 194 | |
| 195 | - ``V4L2_ENC_IDX_FRAME_MASK`` |
| 196 | |
| 197 | - 0x0F |
| 198 | |
| 199 | - *AND* the flags field with this mask to obtain the picture coding |
| 200 | type. |
| 201 | |
| 202 | |
| 203 | |
| 204 | Return Value |
| 205 | ============ |
| 206 | |
| 207 | On success 0 is returned, on error -1 and the ``errno`` variable is set |
| 208 | appropriately. The generic error codes are described at the |
| 209 | :ref:`Generic Error Codes <gen-errors>` chapter. |
| 210 | |
| 211 | |
| 212 | .. ------------------------------------------------------------------------------ |
| 213 | .. This file was automatically converted from DocBook-XML with the dbxml |
| 214 | .. library (https://github.com/return42/sphkerneldoc). The origin XML comes |
| 215 | .. from the linux kernel, refer to: |
| 216 | .. |
| 217 | .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook |
| 218 | .. ------------------------------------------------------------------------------ |