[FFmpeg-user] Help needed to work around incorrect DTS when capturing H264 from a Logitech C920

Peter Rabbitson rabbit+list at rabbit.us
Tue Dec 16 11:55:51 CET 2014

On 12/16/2014 11:25 AM, Georgi Chorbadzhiyski wrote:
> On 12/16/2014 11:07 AM, Peter Rabbitson wrote:
>> On 12/15/2014 06:49 PM, Carl Eugen Hoyos wrote:
>>> Peter Rabbitson <rabbit+list <at> rabbit.us> writes:
>>>> ffmpeg -r 30 -f v4l2 -s 1920x1080 -vcodec h264
>>> I believe -r 30 does not do what you think it does
>>> and it may be the reason for the issues you see.
>>> Is there a problem if you remove it?
>>>> -i /dev/v4l/by-id/*HD_Pro_Webcam_C920* \
>>>>      -c:v copy -f matroska -
> I've used Logitech C920 and noticed that the camera drops it's frame rate
> without signaling it. So what happened was that I was seeing stuttering
> in high resolutions and only when I dropped the camera resolution to 640x480
> I was able to get steady input fps.
> The lowering of frame rate occurred when the camera lens do not receive
> enough light.
> You are may be seeing similar problem.

Ha! This may very well be my problem... Could you please look at the 
video at http://vimeo.com/114550042 and tell me if this "feels" similar 
to the stuttering you were witnessing? As first order of business I want 
to find out if my particular camera is to blame, or there is something 
happening with the cmera->driver pipeline.

I tried with more light and smaller frame-size - didn't notice any 

I guess next step is the USB device redirected to a windows VM and 
trying things with a windows version of ffmpeg. Bleh!

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