[FFmpeg-devel] soundtouch filter?
michaelni at gmx.at
Tue May 15 18:13:15 CEST 2012
On Tue, May 15, 2012 at 12:30:32AM -0600, Pavel Koshevoy wrote:
> On 4/29/12 2:56 PM, Pavel Koshevoy wrote:
> >On 04/29/2012 09:50 AM, Reimar Döffinger wrote:
> >>Hello Pavel,
> >>it seems I can't send anything to the list at the moment, so direct
> >>answer instead...
> >>On Sun, Apr 29, 2012 at 08:36:02AM -0600, Pavel Koshevoy wrote:
> >>>SoundTouch is LGPL. However, I am fine with GPL. What existing
> >>>avfilter code is a good reference for me to use for scaletempo port?
> >>I don't really know, but af_aresample does the kind of pts fiddling you
> >>asked about and is not that large since most of the "heavy
> >>lifting" code is in
> >>So that might be a good starting point.
> >OK, I had a quick look at scaletempo, it implements WSOLA. I had
> >a look at SoundTouch, it appears to implement SOLA. I looked at
> >WSOLA paper, it's not terribly enlightening. This article
> >http://www.surina.net/article/time-and-pitch-scaling.html by
> >SoundTouch author is much easier to understand. I am thinking I
> >may not need to port this filter from mplayer, I'll try to
> >implement it from scratch first, maybe use ffmpeg rdft functions
> >for cross correlation calculation.
> >It also occurs to me that this filter needs to modify timestamps
> >not only for audio but also for video and subtitles, otherwise
> >they'll go out of sync. Is this going to be a problem?
> >Thank you,
> > Pavel.
> OK, I now have my own implementation of WSOLA filter. It didn't use
> cross-correlation for audio fragment alignment, I've used a
> multi-resolution pyramid registration approach instead for
> performance reasons -- O(N).
> My implementation is just a couple of C++ template classes
> parameterized by the sample type (unsigned char, short int, int,
> float). The filter supports multi-channel audio. I've already
> integrated it into my ffmpeg based video player, but not as an
> avfilter (because I don't want that overhead).
> The filter files are here:
> So, is it worth trying to wrap it as an avfilter and add it to ffmpeg?
sure it would be very welcome but keep in mind ffmpeg is C not C++
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
When the tyrant has disposed of foreign enemies by conquest or treaty, and
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