dropping frames when using v4l2src

[Nicolas Dufresne]

Le 2014-11-11 11:34, Aleksander Dutkowski a écrit :
>
> Moreover, when using gstreamer 1.0 it tells me:
> WARNING: from element 
> /GstPipeline:pipeline0/GstAutoVideoSink:autovideosink0/GstXvImageSink:autovideosink0-actual-sink-xvimage: 
> A lot of buffers are being dropped.
> Additional debug info:
> /var/tmp/portage/media-libs/gstreamer-1.2.4-r2/work/gstreamer-1.2.4/libs/gst/base/gstbasesink.c(2791): 
> gst_base_sink_is_too_late (): 
> /GstPipeline:pipeline0/GstAutoVideoSink:autovideosink0/GstXvImageSink:autovideosink0-actual-sink-xvimage:
> There may be a timestamping problem, or this computer is too slow.
>
> Is this an issue with my cam (logitech quickcam communicate stx) or 
> with the pipes? Computer is not slow (8 cores, 16G of ram).

Could be multiple issues.

a) Maybe jpegdec has 1 frame latency, but does not say so
b) Maybe you have a webcam (most of them do) that reduce framerate on 
low light
c) Maybe you are lucky enough that you have a buggy cam that produce 
wrong timestamp
d) PC not fast enough (unlikely)

For a), we just have to look in the code (will do and come back). For 
b), I don't know exactly the solution to that. You test if it's a) 
and/or b) by disabling sync, sync=f0 to xvimagesink (not a solution, 
just a way to confirm).

For c), I own one of these cam which has embedded firmware bug. I've 
implement code to detect that in git master.

Even though unlikely, d) would mean 1 of your 8 core (jpegdec is single 
threaded) is saturated. You can confirm this by setting sync=false and 
checking if gst-launch-1.0 is around 100% (in top).

Nicolas