VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD — Execute an encoder command
|struct v4l2_encoder_cmd *argp|
File descriptor returned by
These ioctls control an audio/video (usually MPEG-) encoder.
VIDIOC_ENCODER_CMD sends a command to the
VIDIOC_TRY_ENCODER_CMD can be used to
try a command without actually executing it.
To send a command applications must initialize all fields of a
struct v4l2_encoder_cmd and call
VIDIOC_TRY_ENCODER_CMD with a pointer to this
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.
VIDIOC_STREAMON call sends an implicit
START command to the encoder if it has not been started yet. After a STOP command,
read() calls will read the remaining data
buffered by the driver. When the buffer is empty,
read() will return zero and the next
read() call will restart the encoder.
VIDIOC_STREAMOFF call of a streaming
file descriptor sends an implicit immediate STOP to the encoder, and all buffered
data is discarded.
These ioctls are optional, not all drivers may support them. They were introduced in Linux 2.6.21.
Table A.20. struct v4l2_encoder_cmd
|__u32||The encoder command, see Table A.21, “Encoder Commands”.|
|__u32||Flags to go with the command, see Table A.22, “Encoder Command Flags”. If no flags are defined for this command, drivers and applications must set this field to zero.|
|__u32||Reserved for future extensions. Drivers and applications must set the array to zero.|
Table A.21. Encoder Commands
|0||Start the encoder. When the encoder is already running or paused, this command does nothing. No flags are defined for this command.|
|1||Stop the encoder. When the
|2||Pause the encoder. When the encoder has not been started yet, the driver will return an EPERM error code. When the encoder is already paused, this command does nothing. No flags are defined for this command.|
|3||Resume encoding after a PAUSE command. When the encoder has not been started yet, the driver will return an EPERM error code. When the encoder is already running, this command does nothing. No flags are defined for this command.|
Table A.22. Encoder Command Flags
|0x0001||Stop encoding at the end of the current Group Of Pictures, rather than immediately.|
On success 0 is returned, on error -1 and the
errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.
cmd field is invalid.
The application sent a PAUSE or RESUME command when the encoder was not running.