[FFmpeg-devel] [GSoC] Qualification Task

[Michael Niedermayer]

On Wed, Mar 23, 2011 at 05:44:48AM +0200, Mina Nagy Zaki wrote:
> On Tuesday 22 March 2011 16:14:28 Stefano Sabatini wrote:
> > From a private mail I received on 2011-01-28:
> > > Attached is the most recent patch I could find. There is a bottleneck
> > > however with sox:
> > > 
> > > The sox API that starts off the filtering of data - sox_flow_effects() -
> > > keeps trying to pull data from the input effect defined in lavfi until
> > > it sends EOF, otherwise doesn't return. So I changed the af_sox input
> > > effect behavior in the patch below to always send EOF after giving every
> > > buffer to the sox chain. This means the sox chain would be reinitialized
> > > when calling sox_flow_effects for each audio buffer. This causes sox to
> > > crash after playing out a few buffers.
> > > 
> > > Instead, it might be better to call sox_flow_effects once in a new
> > > thread and let it fetch and output its buffers from/to the FIFOs at the
> > > input and output.
> > > 
> > > Hope that helps.
> > > 
> > > Regards,
> > > Hemanth
> > 
> > Attached patch, compile but completely untested. You need to configure
> > FFmpeg with --enable-libsox.
> 
> This continuously re-initializes all the effects, and then drains all the 
> effects, on every new lavfi buffer. The only way to get this to work is to put it 
> in a thread and let it block on input, or create our own customized 
> sox_flow_effects()
> 
> I tested it with the earwax effect (which doesn't even need draining...) and as 
> expected it eats up the buffer then segfaults when it tries to sox_flow_effects() 
> again.
> 
> The solution I see best is IMHO simply doing one sox effect per lavfi sox 
> wrapper instance as I mentioned earlier, and as Peter later added. We simply 
> create and initialize one effect and flow samples through it as they arrive. 
> This way we can bypass a lot of the problems, and we don't have to write code 
> to handle sox chains, but instead let the lavfi code do its thing.

i agree that 1 wraper instance should only contain 1 filter instance


[...]
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