theora dev - Feb 2010 - Cortado gapless looping

(Sorry, I registered from one email address then sent this from another 
email address ... sending this from the correct one now, sorry if it 
eventually goes through twice)

I''m wondering if it would be feasible to add gapless looping support to
Cortado. Specifically I''m interested in gapless looping of Vorbis audio
(as background music for a web game). To be clear, I don''t want
crossfading, overlap or anything like that, I want the first sample of a
audio file to follow the last sample, and so forth.

I''ve been looking in to adding it myself, but I''m not used to
Java
enough to digest a project that complex. So I''m hoping that somebody
with more indepth knowledge of Cortado could give me some tips on where
I need to add it. I figure there are a few possible places ... there
could be a class that abstracts an ogg file and presents it as a stream
of the same ogg file over and over again, or at a higher level whatever
is buffering the audio could understand how to reread any file type ...
but I''m not sure where or how to implement either of these :)

Any help appreciated.

- Gregor Richards

Gregor Richards wrote:
> I''ve been looking in to adding it myself, but I''m not
used to Java
> enough to digest a project that complex. So I''m hoping that
somebody
> with more indepth knowledge of Cortado could give me some tips on where
> I need to add it. I figure there are a few possible places ... there
> could be a class that abstracts an ogg file and presents it as a stream
> of the same ogg file over and over again, or at a higher level whatever
> is buffering the audio could understand how to reread any file type ...
> but I''m not sure where or how to implement either of these :)
The principal difficulty I see with looping is avoiding downloading the
file over and over again.

In Cortado, I believe that every "seek" event (e.g. restarting the
stream)
causes all current buffers to be dropped.  This makes sense because
Cortado is designed to handle large files, and cannot touch the disk.
Cortado only buffers ahead of the current playback point, for streaming.
I imagine that you don''t want users to be downloading your loop over
and
over again; otherwise you could just stream it continuously from the server.

One relatively easy hack would be to forgo all the http streaming, and
instead ship the vorbis file inside the .jar.  This would simplify your
life considerably, but would force users to download the entire loop
before initiating playback.  It''s also less reusable than one might
like.

The ideal solution would involve augmenting the buffering logic to allow
caching of entire files, up to some size limit, so that one may loop back
to the beginning.  My best idea on how to accomplish this is to
(optionally) cache the file inside HTTPSrc.  Even after that, some
trickery would be needed for gapless playback.  OggDemux would probably
require a "loop" flag, which would cause it to seek to the beginning
if it
receives an End Of Stream (EOS) message, instead of passing forward the EOS.

By the way, Cortado''s internal design is very close to Gstreamer 0.10.
Reading the gstreamer docs may help to understand what''s going on.

Feel free to keep asking questions here, of course.

--Ben



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