ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD

&manvol;

VIDIOC_ENCODER_CMD

VIDIOC_TRY_ENCODER_CMD

Execute an encoder command

    	int ioctl
    	int fd
    	int request
    	struct v4l2_encoder_cmd *argp

## Arguments

`fd`

- &fd;

`request`

- VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD

`argp`

## Description

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 &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`() or &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.

A `close`() or &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.

## struct v4l2_encoder_cmd

&cs-str;
__u32 | cmd | The encoder command, see encoder-cmds.
__u32 | flags | Flags to go with the command, see encoder-flags. 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.

## Encoder Commands

&cs-def;
`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. 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 VIDIOC_DQBUF ioctl will not block anymore, but return an &EPIPE;.
`V4L2_ENC_CMD_PAUSE` | 2 | Pause the encoder. When the encoder has not been started yet, the driver will return an &EPERM;. 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;. When the encoder is already running, this command does nothing. No flags are defined for this command.

## Encoder Command Flags

&cs-def;
`V4L2_ENC_CMD_STOP_AT_GOP_END` | 0x0001 | Stop encoding at the end of the current Group Of Pictures, rather than immediately.

&return-value;

EINVAL

- The cmd field is invalid.

EPERM

- The application sent a PAUSE or RESUME command when the encoder was not running.