Make it possible to specify MJPEG quality through Video4Linux2 controls

[curtishall]

Imported from Redmine:

http://improve.bluecherrydvr.com/issues/930

Would it be possible to allow modification of MJPEG quality through the "v4l2-ctl --set-jpeg-comp" command? In our company we would require to switch this value on the fly so we can take high-quality screenshots while keeping the MJPEG video streaming easy on the bandwidth.

Updated by Robert Zalewski

ioctl requests which correspond to the get/set commands are described here: http://v4l2spec.bytesex.org/spec/r11285.htm
Also "v4l2-ctl --help" command prints out this text under "Uncommon options"

--get-jpeg-comp query the JPEG compression [VIDIOC_G_JPEGCOMP]
--set-jpeg-comp=quality=,markers=,comment=,app=
set the JPEG compression [VIDIOC_S_JPEGCOMP]
is the app segment: 0-9 or a-f, is the actual string.
is a colon separated list of:
dht: Define Huffman Tables
dqt: Define Quantization Tables
dri: Define Restart Interval

[JackSimth]

This is noted from 2 years ago... Has this happened? I would like to have the same feature available for the BC-H16480A-REV2 16-port 150 fps h.264 card I have for testing.

[curtishall]

Not yet. It's eventually planned and might be looked at again in the next month or two.

Optionally we accept pull requests, if you wanted to implement this yourself. I can provide you the technical datasheets on the chips.

[ghost]

@JackSimth now we have the quality setting for H264 encoder: b6a9568
If you use exactly MJPEG encoder, please indicate in this topic, we can add that control similarly.