[linux-uvc-devel] [Bug] Logitech C920 capture broken by UVC timestamp support (66847ef)

[Peter Rabbitson]

Hi!

After a lot of trial an error I bisected the bug down to this commit:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=66847ef

A simple capture command like this:

ffmpeg -f v4l2 -s 1920x1080 -vcodec h264 \
-i /dev/v4l/by-id/usb-*HD_Pro_Webcam_C920* \
-c copy -copyinkf -f matroska rec_cam.mkv

Works fine up to the parent of this commit (25738cb), but from 66847ef
onwards there is a noticeable "stutter" every ~2.5 seconds. An example
can be seen here: https://vimeo.com/114550042

This problem has been observed by others as well, but it seems it has
not been bisected up untill now:
https://trac.ffmpeg.org/ticket/3956
http://permalink.gmane.org/gmane.comp.video.ffmpeg.user/55069

Please let me know if I can help with resolving this (I have the
hardware and the ability to run a custom kernel).

Cheers

[Peter Rabbitson]

Post by Peter Rabbitson
Hi!
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=66847ef
ffmpeg -f v4l2 -s 1920x1080 -vcodec h264 \
-i /dev/v4l/by-id/usb-*HD_Pro_Webcam_C920* \
-c copy -copyinkf -f matroska rec_cam.mkv
Works fine up to the parent of this commit (25738cb), but from 66847ef
onwards there is a noticeable "stutter" every ~2.5 seconds. An example
can be seen here: https://vimeo.com/114550042

Is there something else I can capture/provide before Christmas that will
help with looking into this? Given the multitude of debug/tracing
options I am not sure where to start/what would be helpful.

Thanks!