gstreamer v4l2 sync parameter meaning

[Nicolas Dufresne]

Hi,

Le lun. 28 août 2023, 13 h 45, Regine Issan via gstreamer-devel <
gstreamer-devel at lists.freedesktop.org> a écrit :

> Hello Dear community,
> I am using gstreamer to stream files from  disk to  (v4l2)  video device.
> the gst-launch commands (below) seems to work for small files.
>
> However, when i run the command with  4k files ,for example, i get the
> error:
> "There may be a timestamping problem, or this computer is too slow.".
>

Your computer is too slow is the most likely cause.


> when i add  sync = 0 to the end of the gst-launch commands (below), the
> error disappers.
>

This property controls if GStreamer should playback at the appropriate rate
or not care.


> could anyone  please advise:
> 1. what cases the error ?
> 2. what is the meaning of the fix ?
>     what am i loosing by setting   "v4l2sink sync=0" \   "xvimagesink
> sync=0"  ?
>    does that mean theat gstreamer does not guantee to the frame rate
> specified in the command  (30/1) ?
>
>    PS: documentation only tells "Sync on the clock"
>
>
> Thank you !!!
>
> More details:
>
> command to inject to screen:
> gst-launch-1.0 -v multifilesrc location=./%04d.png loop=1
> caps="image/png,framerate=30/1" ! pngdec ! videoconvert  ! xvimagesink
>
> command to inject to virtual video device:
>  gst-launch-1.0 -v multifilesrc location=./%04d.png loop=1
> caps="image/png,framerate=30/1" ! pngdec ! videoconvert  !
> "video/x-raw,format=YUY2" ! v4l2sink device=/dev/video11
>

In this pipeline you have multiple heavy CPU operation, all running on one
CPU/thread.

- pngdec
- videoconvert from RGB to YUV

You can use more CPUs by a) adding queue element after heavy operations and
b) configure videoconvert to use multiple threads (n-threads property).



>
> Detailed error:
> There may be a timestamping problem, or this computer is too slow.
>                 WARNING: from element
> /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0: A lot of buffers are being
> dropped.
>                 Additional debug info:
>                 ../libs/gst/base/gstbasesink.c(3143):
> gst_base_sink_is_too_late (): /GstPipeline:pipeline0/GstV4l2Sink:v4l2sink0:
>
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