flac dev - Dec 2010 - OggFLAC streaming is systemically broken.

Not that many people are streaming FLAC, and if they are, they are, in
my mind, undoubtedly experiencing problems. Probably the most prized
kind of software problem of all, the intermittent kind.

I am streaming FLAC. 24bit no less, and its fantastic. The future I
would like to live in, is one where lossless music is streamed and
heard by people other than myself.

It is generally not possible to stream flac correctly with the current
libflac 1.2.1, unless your into epic kludges. There is at-least one
issue in libflac, and issues in decoding clients such as VLC, mplayer
and totem.

The good news is that one can hackfix libflac on the server side and
produce a valid stream that VLC and mplayer can take in without issue.
Totem seems to have other issues I have not investigated.

There seems to be two problems conspiring together. Both have to do
with silence. Even though what we really want to do is listen to music
or someone yapping, silence manages to be very important, be it a few
second in a song or long periods of dead air. Problem number one that
when libflac is pumping out silent subframes, the ogg pages are never
getting flushed out, because they are so small. So until there is some
noise or the page is full, the client decoder is left hanging. Then
when it starts decoding again, its decoding silence, and thus falls
far behind in the stream, probably confusing itself and disconnecting.
Problem number two, is even if you flush these little guys.. the
clients still get confused, especially if there is more than one per
page.

The epic kludge solution is to just never let there be any perfect
silence, not even for a few ms, plug in an old am radio and crank it
to just barely audible and add that to the stream.

The hackfix, is to disable constant subframes, and flush any packet
less than say 700 bytes, otherwise use pageout as normal.

The sustainable solution would probably be to add an option to libflac
to force flush the stream after X number of samples, and then fix all
of the clients. Then live the dream of streaming lossless audio.

Here is my hackfix:

https://github.com/oneman/libflac/commit/67e13364032404ebc1837af143fdd1cd81786c3a

I hope you like it.

Cheers,

David Richards

Thanks for looking into things like this.  Streaming 24-bit FLAC  
seems like a great idea.

P.S.  Rather than resorting to something esoteric like plugging in an  
old AM radio, perhaps you could use a more prevalent audio process  
like dithering (maybe even with noise shaping) to produce non-zero  
frames - assuming your hack continues to be necessary.  Depending  
upon the source of your audio, there's a slight chance that dithering  
would be beneficial anyway.

Brian Willoughby
Sound Consulting


On Dec 1, 2010, at 01:28, David Richards wrote:
> I am streaming FLAC. 24bit no less, and its fantastic. The future I
> would like to live in, is one where lossless music is streamed and
> heard by people other than myself.
>
> It is generally not possible to stream flac correctly with the current
> libflac 1.2.1, unless your into epic kludges. There is at-least one
> issue in libflac, and issues in decoding clients such as VLC, mplayer
> and totem.
>
> The good news is that one can hackfix libflac on the server side and
> produce a valid stream that VLC and mplayer can take in without issue.
> Totem seems to have other issues I have not investigated.
>
> There seems to be two problems conspiring together. Both have to do
> with silence. Even though what we really want to do is listen to music
> or someone yapping, silence manages to be very important, be it a few
> second in a song or long periods of dead air. Problem number one that
> when libflac is pumping out silent subframes, the ogg pages are never
> getting flushed out, because they are so small. So until there is some
> noise or the page is full, the client decoder is left hanging. Then
> when it starts decoding again, its decoding silence, and thus falls
> far behind in the stream, probably confusing itself and disconnecting.
> Problem number two, is even if you flush these little guys.. the
> clients still get confused, especially if there is more than one per
> page.
>
> The epic kludge solution is to just never let there be any perfect
> silence, not even for a few ms, plug in an old am radio and crank it
> to just barely audible and add that to the stream.
>
> The hackfix, is to disable constant subframes, and flush any packet
> less than say 700 bytes, otherwise use pageout as normal.
>
> The sustainable solution would probably be to add an option to libflac
> to force flush the stream after X number of samples, and then fix all
> of the clients. Then live the dream of streaming lossless audio.