[Savonet-users] Support for ALAC files in faad plugin?

[Daniel J. <dan...@so...>]

Hi all,

Regarding http://dev.sourcefabric.org/browse/CC-4996 we have found that
Liquidsoap does not distinguish between MPEG-4 audio files containing
AAC encoded audio and those containing ALAC encoded audio, aka Apple
Lossless (see http://alac.macosforge.org/). However at decoding time,
playout fails for ALAC files.

Using a test ALAC file from
http://www.linnrecords.com/linn-downloads-testfiles.aspx you can see
that ALAC files use the same extension and mime type as AAC, even though
the codec is different:

mutagen-inspect recit16bit.m4a
– recit16bit.m4a

    MPEG-4 audio, 9.01 seconds, 0 bps (audio/mp4)

The Airtime function liquidsoapFilePlayabilityTest (line 1077 of
https://github.com/sourcefabric/Airtime/blob/master/airtime_mvc/application/models/StoredFile.php)
uses output.dummy which returns OK for an ALAC file. However if you use
output.alsa instead, you will see the error:

Decoder "MP4" betrayed us on "recit16bit.m4a"!

Assuming this error refers to the faad plugin for Liquidsoap, it seems
faad can be patched to support ALAC, but this patch has not been applied
upstream:

https://sourceforge.net/p/faac/bugs/183/

I'd be interested to know if people think this is worth fixing, or
whether we should simply tell people to re-encode their ALAC audio as
FLAC. I'm all in favour of FLAC, but understand that some people need
interoperability with Apple products that support ALAC but do not
support FLAC.

Cheers!

Daniel