[mythtv] [PATCH] time stretch with libsoundtouch

Ross Campbell ross.campbell at gmail.com
Tue Nov 2 02:27:41 UTC 2004

> > enough...  I think your algorithm is one of those which tries to
> > preserve the resonanances in the human voice to try and make it still
> > sound natural?  Stops the chipmunking effect.

I think this feature is fantastic, and as much as another library
dependency is frowned upon in myth, I'd like to lobby *for* this

It's way more than just enhanced fast forward or rewind. This would provide:

- Ability to watch mostly spoken TV at much higher speeds and compress
your learning/watching time while getting all of the content out of

- slowing down sports plays to provide fantastic instant replay with
all associated commentary

- slowing down complex musical passages to deconstruct melody/rhythms
(like Amazing Slow Downer - http://www.ronimusic.com)

- slow down educational or foreign language material to increase comprehension

Here is a good PDF with some experiments about "acceptable" time scale
modifications: http://citeseer.ist.psu.edu/cache/papers/cs/26467/http:zSzzSzwww.ece.ogi.eduzSz~gileadzSzdoczSztsm_hicss2000.pdf/amir00using.pdf

Much video content can be time scaled to 1.2X speed with little change
in user perception, and "for news clips and the training clips
comprehension remains at a high level up to a speedup .. which is 1.2
times higher than its natural speedup... For the talk clips,
comprehension reaches maximum at speedup ratio of 0.83"

I believe if MythTV adds support for WSOLA (waveform similarity
overlap-add) time shifting, we stand to greatly increase the scope of
mythtv by turing it into an educational tool as well as the mythical
convergence device.

I could imagine mythtv as a frontend for recorded lectures at
universities... and students reviewing lectures at 20% speed increase
or 20% speed decrease depending on desired effect.

> get it from http://www.digivation.com.au/mythtv_timestretch.patch.zip
> fewer files and no contructor and reconfigure mods required. also no
> transcode dependency. cleaner all round.
> still need to get MMX going as it seems to be faulty but works fully without


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