Experimental: This is an experimental interface and may change in the future.
These ioctls control an audio/video (usually MPEG-) encoder.
VIDIOC_ENCODER_CMD sends a command to the
encoder, 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_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.
A read() call sends a 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.
A close() call sends an 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 1. struct v4l2_encoder_cmd
| __u32 | cmd | The encoder command, see Table 2. |
| __u32 | flags | Flags to go with the command, see Table 3. If no flags are defined for this command, drivers and applications must set this field to zero. |
| __u32 | data[8] | Reserved for future extensions. Drivers and applications must set the array to zero. |
Table 2. Encoder Commands
V4L2_ENC_CMD_START | 0 | Start the encoder. When the encoder is already running or paused, this command does nothing. No flags are defined for this command. |
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. |
V4L2_ENC_CMD_PAUSE | 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. |
V4L2_ENC_CMD_RESUME | 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. |