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diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-enc-index.rst b/Documentation/userspace-api/media/v4l/vidioc-g-enc-index.rst new file mode 100644 index 000000000..c6792bbe3 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-g-enc-index.rst @@ -0,0 +1,144 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _VIDIOC_G_ENC_INDEX: + +************************ +ioctl VIDIOC_G_ENC_INDEX +************************ + +Name +==== + +VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream + +Synopsis +======== + +.. c:macro:: VIDIOC_G_ENC_INDEX + +``int ioctl(int fd, VIDIOC_G_ENC_INDEX, struct v4l2_enc_idx *argp)`` + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``argp`` + Pointer to struct :c:type:`v4l2_enc_idx`. + +Description +=========== + +The :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` ioctl provides meta data about a compressed +video stream the same or another application currently reads from the +driver, which is useful for random access into the stream without +decoding it. + +To read the data applications must call :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` with a +pointer to a struct :c:type:`v4l2_enc_idx`. On success +the driver fills the ``entry`` array, stores the number of elements +written in the ``entries`` field, and initializes the ``entries_cap`` +field. + +Each element of the ``entry`` array contains meta data about one +picture. A :ref:`VIDIOC_G_ENC_INDEX <VIDIOC_G_ENC_INDEX>` call reads up to +``V4L2_ENC_IDX_ENTRIES`` entries from a driver buffer, which can hold up +to ``entries_cap`` entries. This number can be lower or higher than +``V4L2_ENC_IDX_ENTRIES``, but not zero. When the application fails to +read the meta data in time the oldest entries will be lost. When the +buffer is empty or no capturing/encoding is in progress, ``entries`` +will be zero. + +Currently this ioctl is only defined for MPEG-2 program streams and +video elementary streams. + +.. tabularcolumns:: |p{4.2cm}|p{6.2cm}|p{6.9cm}| + +.. c:type:: v4l2_enc_idx + +.. flat-table:: struct v4l2_enc_idx + :header-rows: 0 + :stub-columns: 0 + :widths: 1 3 8 + + * - __u32 + - ``entries`` + - The number of entries the driver stored in the ``entry`` array. + * - __u32 + - ``entries_cap`` + - The number of entries the driver can buffer. Must be greater than + zero. + * - __u32 + - ``reserved``\ [4] + - Reserved for future extensions. Drivers must set the + array to zero. + * - struct :c:type:`v4l2_enc_idx_entry` + - ``entry``\ [``V4L2_ENC_IDX_ENTRIES``] + - Meta data about a compressed video stream. Each element of the + array corresponds to one picture, sorted in ascending order by + their ``offset``. + + +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}| + +.. c:type:: v4l2_enc_idx_entry + +.. flat-table:: struct v4l2_enc_idx_entry + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u64 + - ``offset`` + - The offset in bytes from the beginning of the compressed video + stream to the beginning of this picture, that is a *PES packet + header* as defined in :ref:`mpeg2part1` or a *picture header* as + defined in :ref:`mpeg2part2`. When the encoder is stopped, the + driver resets the offset to zero. + * - __u64 + - ``pts`` + - The 33 bit *Presentation Time Stamp* of this picture as defined in + :ref:`mpeg2part1`. + * - __u32 + - ``length`` + - The length of this picture in bytes. + * - __u32 + - ``flags`` + - Flags containing the coding type of this picture, see + :ref:`enc-idx-flags`. + * - __u32 + - ``reserved``\ [2] + - Reserved for future extensions. Drivers must set the array to + zero. + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}| + +.. _enc-idx-flags: + +.. flat-table:: Index Entry Flags + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_ENC_IDX_FRAME_I`` + - 0x00 + - This is an Intra-coded picture. + * - ``V4L2_ENC_IDX_FRAME_P`` + - 0x01 + - This is a Predictive-coded picture. + * - ``V4L2_ENC_IDX_FRAME_B`` + - 0x02 + - This is a Bidirectionally predictive-coded picture. + * - ``V4L2_ENC_IDX_FRAME_MASK`` + - 0x0F + - *AND* the flags field with this mask to obtain the picture coding + type. + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. |