[vorbis] Format converters

[Moritz Grimm]

"R.J.J.H. van Son" wrote:
> Are direct bit-rate converters possible for Ogg Vorbis? Or do they
> already exist?

Eventually, it will be possible to convert high-bitrate .ogg files to
lower bitrate versions without having to reencode. That's called
"peeling" and the tools to do so don't exist yet. However, the .ogg
files you create now will be perfectly peelable in the future, once
those tools exist.

> Now, a new project would switch to Minidisc (ATRAC3) recordings,
> transferring them to the lap-top/CD-ROM in compressed form (e.g., Ogg
> Vorbis, 80 kbs would do). Finally this speech would end up in a huge
> speech corpus for small languages, which uses a different compression
> codec and another bit-rate for archiving, say MP3 at 192 kbs.

Afaik, ATRAC is a pretty high-bitrate codec, so I don't see any serious
problems re-encoding that stuff to something much smaller. However,
re-encoding those -q 2 Ogg Vorbis files to anything higher, like MP3 @
192kbps makes absolutely no sense - that's a waste of space. The files
will be bigger, while sounding either equal or worse than the q2 .ogg
files.

The less re-encoding the better. Go directly from ATRAC to MP3 at 192kbps
and from ATRAC to Vorbis at q2, etc pp.

Alternatively, since you say that there's a notebook involved, record
the speeches (or at least as much as possible, with that notebook &
solar gear) directly to harddisk in .wav format and then encode that to
Ogg Vorbis in some insane quality. You can peel those files lateron and
you keep enough quality to have a decent result when reencoding that to
your corpus delicti MP3 @ 192kbps. This might work pretty well -
44.1kHz/16bit/mono takes 5MB/min, so there is quite a few hours of
constant recording possible on today's notebooks harddisks.

IF you can't get around re-encoding (it is not possible to "translate"
the audio files from one format (e.g. Vorbis) to another (MP3) without
loss), reencode as few times as possible. This applies to *all* lossy
codecs - none that I know of can be transcoded into each other (when I
say "transcode" i mean the lossless translation from one format into the
other ... others use it for "re-encoding", so there might be some
confusion).

<p>Moritz
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