[Matroska-devel] Stereoscopic playback

Steve Lhomme steve.lhomme at free.fr
Sun Nov 12 17:40:33 CET 2006


Hi,

David Duffy wrote:
> I don't need to play backwards as such (at least not every frame), I just need the best/most efficient way to scan for keyframes in reverse order to provide a "fast rewind" to go along with fast forward.  I'm just trying to do fast forward and rewind like on a DVD player or VCR.  Fast forward works okay by just ignoring frames that are not key frames.
> If it isn't doable then I'll have to figure something else out I guess.
> Thank-you. :)
> P.S. I'm not overly worried about being efficient in this scenario.

Unfortunately the issue here is not only in matroska. If you seek 
backward the previous frame you're looking for might be a B frame that 
needs 2 P frames to be decoded, themselves needing other frames to be 
decoded. So basically you'd need to go to the previous keyframe and 
cache all the frames in between. That's a lot of data ! So if you want 
to avoid such tricky situations, use only keyframes or very little P 
frames (1 or 2 between keyframes). Then the normal matroska seeking will 
do just fine.

Steve

> ----- Original Message ----
> From: Mike Matsnev <mike at po.cs.msu.su>
> To: Discussion about the current and future development of Matroska <matroska-devel at lists.matroska.org>
> Sent: Tuesday, 7 November, 2006 1:12:30 AM
> Subject: Re: [Matroska-devel] Stereoscopic playback
> 
> On Mon, Nov 06, 2006 at 04:42:26PM +0000, David Duffy wrote:
>> Now, to be a total newb, I need to ask for help rewinding. ;)
>> Mike can you please give me the idiot's guide version of how to use
>> your library correctly to rewind?
> If you mean playing backwards, then it's not supported by the library,
> Matroska isn't really designed for that. This might be implemented, but
> it will be rather ineffective.
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