Oops, I was a bit sloppy in my organization, and also sloppy on a few facts.
I did not intend to imply that A-52 was lossless - I was merely using it as an
example of an open specification format that cannot be implemented and sold
without being licensed. I'm glad that we are finally getting lossless
formats
accepted in large public standards. The liba52 library may not be legal. I
seem to recall some legal repercussions, but perhaps that was only with libdts.
My impression was that AAC is part of MPEG-4 audio because of the .m4a
extension. I further assumed that Apple Lossless is a variation of AAC because
they seem to share a common extension. Maybe I was just hoping that the
reason Apple chose Apple Lossless over FLAC is that Apple Lossless is part of a
larger public specification like MPEG-4 audio, if there is any such thing.
Perhaps I am merely reading too much into the use of the generic MPEG-4
container format.
You are correct that MLP is supported by DVD-Audio. I'm not sure what
DVD-HD
supports, they may be changing their mind. I'm sure DVD-HD will be a
superset
of DVD-Audio.
In closing, perhaps someone has information on the lossless formats that seem
to remain undocumented. Has anyone heard of a libmlp project?
Brian Willoughby
Sound Consulting
Begin forwarded message:
First off, I'm not an expert in this field, but I thought I could
probably answer a few of your questions. If anyone else wants to give a
more complete explanation, please do.
Brian Willoughby wrote:> Hi folks,
>
> I'm trying to get a handle on the many lossless audio formats from
> the perspective of a software developer. I love the FLAC format
> because it is open source and it performs very well. But there is
> also the MLP (Meridian Lossless Packing), AAC (Apple Lossless), and
> probably some Microsoft format(s) that compete in the same feature
> set. These formats all achieve approximately 2:1 compression without
> loss of detail.
AAC is not the same thing as Apple Lossless. AAC is a lossy format and
one of the audio formats in the MPEG-4 specification. It is used by
iTunes and the iTunes Music Service. Apple Lossless is another format
that is also supported by iTunes.
> What I would like to know is where to go to find out the details on
> these formats. Is MLP documented anywhere? It has been accepted as
> an audio format for DVD-HD, so does that mean it must be openly
> documented?
I don't know about DVD-HD, but MLP can also be used on DVD-Audio discs,
so presumably it's part of (or referenced by) that specification.
> Dolby Digital AC-3 is documented as part of the HDTV specification,
> but it cannot be implemented without paying licensing. Well, a
> programmer could implement it based on the specification, but could
> not make a product without licensing.
Dolby Digital, aka AC-3, aka A/52, is not a lossless format. It is used
on DVD-Video discs. There is at least one open source implementation of it:
http://liba52.sourceforge.net/
You are correct about the licensing. Many other audio formats are also
encumbered by patents (MP3 and AAC, for example).
> Also, what about Apple's Lossless format? Is this part of a larger
> specification, like MPEG-4, or is it completely independent? Is it
> documented anywhere?
I believe it's a proprietary Apple thing, and I don't think it's
documented. I believe that iTunes stores Apple Lossless tracks in an
MPEG-4 container, however.
--
Jon