diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/vidioc-encoder-cmd.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-encoder-cmd.rst | 51 |
1 files changed, 31 insertions, 20 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-encoder-cmd.rst b/Documentation/userspace-api/media/v4l/vidioc-encoder-cmd.rst index 16269b3b1715..d0eacce5485e 100644 --- a/Documentation/userspace-api/media/v4l/vidioc-encoder-cmd.rst +++ b/Documentation/userspace-api/media/v4l/vidioc-encoder-cmd.rst @@ -51,25 +51,26 @@ To send a command applications must initialize all fields of a struct ``VIDIOC_ENCODER_CMD`` or ``VIDIOC_TRY_ENCODER_CMD`` with a pointer to this structure. -The ``cmd`` field must contain the command code. The ``flags`` field is -currently only used by the STOP command and contains one bit: If the -``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag is set, encoding will continue -until the end of the current *Group Of Pictures*, otherwise it will stop -immediately. +The ``cmd`` field must contain the command code. Some commands use the +``flags`` field for additional information. -A :ref:`read() <func-read>` or :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` -call sends an implicit START command to the encoder if it has not been -started yet. After a STOP command, :ref:`read() <func-read>` calls will read +After a STOP command, :ref:`read() <func-read>` calls will read the remaining data buffered by the driver. When the buffer is empty, :ref:`read() <func-read>` will return zero and the next :ref:`read() <func-read>` call will restart the encoder. +A :ref:`read() <func-read>` or :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` +call sends an implicit START command to the encoder if it has not been +started yet. Applies to both queues of mem2mem encoders. + A :ref:`close() <func-close>` or :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` call of a streaming file descriptor sends an implicit immediate STOP to -the encoder, and all buffered data is discarded. +the encoder, and all buffered data is discarded. Applies to both queues of +mem2mem encoders. These ioctls are optional, not all drivers may support them. They were -introduced in Linux 2.6.21. +introduced in Linux 2.6.21. They are, however, mandatory for stateful mem2mem +encoders (as further documented in :ref:`encoder`). .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| @@ -109,21 +110,24 @@ introduced in Linux 2.6.21. - 0 - Start the encoder. When the encoder is already running or paused, this command does nothing. No flags are defined for this command. + + For a device implementing the :ref:`encoder`, once the drain sequence + is initiated with the ``V4L2_ENC_CMD_STOP`` command, it must be driven + to completion before this command can be invoked. Any attempt to + invoke the command while the drain sequence is in progress will trigger + an ``EBUSY`` error code. See :ref:`encoder` for more details. * - ``V4L2_ENC_CMD_STOP`` - 1 - Stop the encoder. When the ``V4L2_ENC_CMD_STOP_AT_GOP_END`` flag is set, encoding will continue until the end of the current *Group Of Pictures*, otherwise encoding will stop immediately. When the - encoder is already stopped, this command does nothing. mem2mem - encoders will send a ``V4L2_EVENT_EOS`` event when the last frame - has been encoded and all frames are ready to be dequeued and will - set the ``V4L2_BUF_FLAG_LAST`` buffer flag on the last buffer of - the capture queue to indicate there will be no new buffers - produced to dequeue. This buffer may be empty, indicated by the - driver setting the ``bytesused`` field to 0. Once the - ``V4L2_BUF_FLAG_LAST`` flag was set, the - :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore, - but return an ``EPIPE`` error code. + encoder is already stopped, this command does nothing. + + For a device implementing the :ref:`encoder`, the command will initiate + the drain sequence as documented in :ref:`encoder`. No flags or other + arguments are accepted in this case. Any attempt to invoke the command + again before the sequence completes will trigger an ``EBUSY`` error + code. * - ``V4L2_ENC_CMD_PAUSE`` - 2 - Pause the encoder. When the encoder has not been started yet, the @@ -152,6 +156,8 @@ introduced in Linux 2.6.21. - Stop encoding at the end of the current *Group Of Pictures*, rather than immediately. + Does not apply to :ref:`encoder`. + Return Value ============ @@ -160,6 +166,11 @@ 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. +EBUSY + A drain sequence of a device implementing the :ref:`encoder` is still in + progress. It is not allowed to issue another encoder command until it + completes. + EINVAL The ``cmd`` field is invalid. |