7.10. ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD¶
7.10.1. Name¶
VIDIOC_ENCODER_CMD - VIDIOC_TRY_ENCODER_CMD - Execute an encoder command
7.10.2. Synopsis¶
-
int
ioctl
(int fd, VIDIOC_ENCODER_CMD, struct v4l2_encoder_cmd *argp)¶
-
int
ioctl
(int fd, VIDIOC_TRY_ENCODER_CMD, struct v4l2_encoder_cmd *argp)¶
7.10.3. Arguments¶
fd
- File descriptor returned by open().
argp
- Pointer to struct
v4l2_encoder_cmd
.
7.10.4. 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 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() 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.
-
v4l2_encoder_cmd
¶
__u32 | cmd |
The encoder command, see Encoder Commands. |
__u32 | flags |
Flags to go with the command, see Encoder Command 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. |
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 error code. |
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. |
V4L2_ENC_CMD_STOP_AT_GOP_END |
0x0001 | Stop encoding at the end of the current Group Of Pictures, rather than immediately. |
7.10.5. 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
Generic Error Codes chapter.
- EINVAL
- The
cmd
field is invalid. - EPERM
- The application sent a PAUSE or RESUME command when the encoder was not running.