Why does decklinksrc need sync=FALSE on xvimagesink?

[Sebastian Dröge]

On Di, 2014-05-06 at 14:23 -0400, Stirling Westrup wrote:
> We've been working to integrate input from a BlackMagic video capture card
> into our video-wall application. The limited documentation we got with the
> card indicated we should use decklinksrc and that we should set sync=false
> on the output sink. Sure enough, this works:
> 
> gst-launch-1.0 decklinksrc mode=18 connection=1 ! videoconvert !
> xvimagesink sync=false
> 
> However, if we set sync to true, then output drops immensely; we seem to be
> getting just a few frames a second. The question is: why?  We'd really
> rather not have to have a special exception for one input source to cause
> us to set the sync flag differently on our output, but I can't figure out
> why the decklinksrc needs it in the first place.

That would indicate a bug in the source element. If it only works with
sync=false on the sink, there will be a problem with the timestamps it
is putting on the buffers or the segment it is configuring.

If you run in gst-launch-1.0 with -v and
> decklinksrc ! fakesink silent=false
you will see the segment event(s) and the timestamps. Is something
looking weird there?

-- 
Sebastian Dröge, Centricular Ltd - http://www.centricular.com
Expertise, Straight from the Source
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