gstreamer v4l2 sync parameter meaning

[Regine Issan]

Thank you , Nicolas for your replay .
I appreciate your help !!!


On Wed, Aug 30, 2023 at 13:34 Nicolas Dufresne <nicolas at ndufresne.ca> wrote:

> 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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