7.34. ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP¶
7.34.1. Name¶
VIDIOC_G_JPEGCOMP - VIDIOC_S_JPEGCOMP
7.34.2. Synopsis¶
-
VIDIOC_G_JPEGCOMP
¶
int ioctl(int fd, VIDIOC_G_JPEGCOMP, v4l2_jpegcompression *argp)
-
VIDIOC_S_JPEGCOMP
¶
int ioctl(int fd, VIDIOC_S_JPEGCOMP, const v4l2_jpegcompression *argp)
7.34.3. Arguments¶
fd
File descriptor returned by
open()
.argp
Pointer to struct
v4l2_jpegcompression
.
7.34.4. Description¶
These ioctls are deprecated. New drivers and applications should use JPEG class controls for image quality and JPEG markers control.
[to do]
Ronald Bultje elaborates:
APP is some application-specific information. The application can set it itself, and it’ll be stored in the JPEG-encoded fields (eg; interlacing information for in an AVI or so). COM is the same, but it’s comments, like ‘encoded by me’ or so.
jpeg_markers describes whether the huffman tables, quantization tables and the restart interval information (all JPEG-specific stuff) should be stored in the JPEG-encoded fields. These define how the JPEG field is encoded. If you omit them, applications assume you’ve used standard encoding. You usually do want to add them.
-
v4l2_jpegcompression
¶
int |
|
Deprecated. If V4L2_CID_JPEG_COMPRESSION_QUALITY control is exposed by a driver applications should use it instead and ignore this field. |
int |
|
|
int |
|
|
char |
|
|
int |
|
|
char |
|
|
__u32 |
|
See JPEG Markers Flags. Deprecated. If V4L2_CID_JPEG_ACTIVE_MARKER control is exposed by a driver applications should use it instead and ignore this field. |
|
(1<<3) |
Define Huffman Tables |
|
(1<<4) |
Define Quantization Tables |
|
(1<<5) |
Define Restart Interval |
|
(1<<6) |
Comment segment |
|
(1<<7) |
App segment, driver will always use APP0 |
7.34.5. 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.