[mythtv] [PATCH] time stretch with libsoundtouch

Mark Spieth mark at dclabs.com.au
Tue Nov 2 10:53:28 UTC 2004

> I'm also shooting for pretty high audio quality so if the quality is
> better I'd also like libsamplerate to stay. Tempo-changing would be
> *very* cool though, but maybe it's a bit heavy on the CPU and the
> latency didn't seem that good. I guess a setting or a compile option
> would be in place, perhaps with a fallback to libsamplerate for speed
> change if one doesn't want to use soundtouch?

there is no problem for libsoundtouch and libsamplerate coexisting. this is
how I have implemented it.
libsoundtouch does not even get instantiated until the first non 1.0
stretchfactor set. thus if you dont use it it has no impact. this should
satisfy you I hope.

> I haven't tried Mark's patch yet but I'm planning to. Anyone know how
> much one can "bend" the audio without the chipmunk effect getting too
> bad? I'm thinking that a couple of percent change in speed wouldn't
> affect the pitch that much. I've been planning to try and reimplement
> the audio warp for the AV sync using either libsoundtouch or
> libsamplerate, but I don't know when I'll find the time. I want to take
there is no lipsync problem. I have catered for that by estimating the
amount of sound buffered and calculating the audio timecode as a result so
it matches the warped audio to the video timecodes. seems pretty good.
there is no chipmunk effect. +25% is usable even +50% if they talk a bit
slow. as I said before, I can watch stargate eps at +25% quite easily and it
seems almost normal. they just talk fast.
try it and you'll see. I now cant live without it. also works on mpeg4's and
everything else so as a result it beats windvd's timestretch feature which
only works on mpeg1 and 2. cpu impact is less than I expected. main problem
is the video decode has to happen at a faster rate. audio overhead seems

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