DASH trick play

Sebastian Dröge sebastian at centricular.com
Thu Jun 26 00:27:45 PDT 2014

On Fr, 2014-06-06 at 12:09 +0100, Alex Ashley wrote:
> I am doing some investigations in to trick play with MPEG DASH streams.
> It appears from the code that the rate field in the seek event is being ignored.
> This led me to think about what the correct behaviour should be. For rates > 0 and < 2 the correct behaviour is probably to just feed fragments downstream faster than real time. 

Yes, see what hlsdemux does here. It might also be necessary to teach
qtdemux about using the rate from upstream though.

> For speeds > 2x or < 0, dashdemux should switch to just downloading I frames. To know where the I frames are in a fragment requires parsing sidx and sisx boxes in the fragment. The problem is that qtdemux is the only thing that knows how to parse mp4 boxes.
> I am interested in the views of the gstreamer community on how trick play ought to work with DASH streams. 

I think the best solution for this would be to create some kind of MP4
parsing library (similar to what we have with codecparsers in -bad
already) that allows you to parse MP4-like structures in dashdemux
without duplicating too much code.

But dashdemux is the only place where you can do that, as dashdemux
controls what is downloaded and what not.

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