[gst-1.0] Make videomixer mix raw frames without timing infromation

[Sebastian Dröge]

On Mi, 2015-03-25 at 02:05 -0700, Arjen Veenhuizen wrote:
> Hi,
> 
> In Gst-0.10, the videomixer element mixes frames as they arrive while
> disregarding any timing information. The Gst-0.10 videomixer2 element can be
> used if timing information was relevant. In Gst-1.0 (GIT head), the
> videomixer element behaves like the videomixer2 element in Gst-0.10. 
> 
> I am mixing multiple raw YUV420p streams (using a filesrc-es with proper
> capsfilters directly linked to the videomixer) with no timing information
> whatsoever on each frame. Is there a way to force the Gst-1.0 videomixer
> element to disregard timing information? For now I am timestamping each
> buffer in each videomixer sink pad manually, but this yields a small
> performance penalty and causes more serious infrequent pipeline stalls. 
> 
> Note that the Gst-1.0 videomixer will crash when mixing a raw yuv stream
> from filesrc without do-timestamp=true, e.g.

If you want to mix frames together as they come, does that mean that you
have a live source? In that case you should properly timestamp the
buffers anyway for proper synchronization handling.
Also if you want to mix live pipelines, I would recommend you to upgrade
to latest GIT master and use the compositor element instead. videomixer
has no support for live mixing and will break things :)

If you don't have a live pipeline, who exactly do you want the mixer to
mix frames together? When they arrive in the mixer completely depends on
how fast you can read and how the OS scheduler schedules the different
threads in that case unless you actually look at the timestamps.


Also note that the new mixers mix everything based on the running times
of the streams. If you only have live streams that shouldn't be a
problem, but if you also mix in non-live streams (e.g. file input), you
will have to offset their running time to the time when you want that
stream to appear in the output timeline.

-- 
Sebastian Dröge, Centricular Ltd · http://www.centricular.com
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