Re: Vorbis-/Speex-Audio for Movie-Archiving

On Monday, 13. April 2009 04:30:30 Jean-Marc Valin wrote:
> I've heard that proposal (or variants) thousands of times and it useless
> because:
>
> 1) There's no decent/practical algorithm to separate speech from the
> rest of the soundtrack
> 2) It's fundamentally inefficient unless you have a large number of
> languages (e.g. for two languages, you'd end up encoding three streams
> instead of two)
> 3) Unless you aim for low bit-rate audio below 32 kbps (which is stupid
> considering the size of a video stream), Vorbis will still perform
> better than Speex, even on speech
>
> Point 3) is especially important. People think that as soon as something
> is speech, Speex is automatically better than Vorbis. That's not the
> case. Speex is designed for low bitrate communication (VoIP). It can
> also be used for storing speech files, but then it only makes sense for
> lower rates. Speex can never (and never aimed to) achieve the level of
> transparency that Vorbis can achieve at higher rates.


Hm, that of course makes this whole point useles.

Thanks for making it clear!


- Hannes




>
> Hannes Hauswedell a écrit :
> > Hi everyone,
> >
> > I have been using vorbis for ages as audio codec for archiving movies and
> > I have always been happy with it, but now I have been thinking about two
> > things:
> >
> > I) Multi-channel
> >
> > Up until now I mostly encoded to stereo; now I am thinking of encoding
> > more movies to 4.0 or 5.1. I heard that vorbis does not optimize for
> > channels > 2, i.e. that 6 channels is just stereo*3. AAC is supposed to
> > do this better... Now I really digg vorbis, because its patent-free and
> > grass-roots-developed ;) so this doesnt mean I am switching to aac, but
> > I'd like to know whether this true or if its just FUD.
> > And if it is true, how big do you think the compression advantage of
> > aac5.1 is over vorbis5.1? If it is true, is someone working on changing
> > this or is it low-priority?
> >
> > II) Multi-language
> >
> > I usually archive both the audio stream in original language and in my
> > native language, but I always thought that a lot of space is wasted
> > there, especially when going multi-channel for one or both languages.
> > Wouldn't it be possible to:
> > * encode the audio stream minus the speech in vorbis
> > * encode each language as speex
> > => save a lot of space because 1*vorb+X*spx << X*vorb
> >
> > That would of course require that,
> > a) a container and the players support this
> > b1) the language be available seperate of the other audio on DVD/BD/...
> > OR
> > b2) an efficient algorithm be available for stripping language from
> > background audio
> >
> > concerning b1) is this not the case anyway? I at least got the impression
> > when copying a DVD to .iso whithout one of its audio tracks, after which
> > this track was still available but without speech.
> >
> > concerning b2) I am sure there are intelligent things out there, but
> > maybe a real simple thing would already work (note that I dont actually
> > have a clue about audio encoding or speex in particular):
> >
> > * the main vorbis as the "intersection" of all audio channels
> > * first speech-track in speex as "audio channel 1 - main vorbis"
> > * second speech-track in speex as "audio channel 2 - main vorbis" aso asf
> >
> > When doing this, the speech-tracks of course wouldn't be clean language
> > and the 'main audio-track' not completely free of language, but who
> > cares, since the 'main-audio-track' is always played concurrently with
> > one one of the speech-tracks. Of course speex would have to be able to
> > efficiently encode language with a little mumble-jumble of other
> > lanugages subtracted ;)
> >
> > Has anyone ever thought about this or is it complete and utter nonsense?
> >
> >
> > Thanks for your time and of course for developing the best free
> > audio-codecs!
> >
> > Regards,
> > Hannes
> >
> >
> >
> >
> >
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