Fraunhofer has begun marketing HD-AAC, ISO MPEG-4 AAC-LC & SLS Options

[rpp3po]

Fraunhofer IIS just presented HD-AAC at the Consumer Electronics Show in Las Vegas. It's a hybrid format which can be played back as conventional AAC on legacy devices. HD-AAC capable devices also read the SLS layer and get a lossless reconstruction of the original signal.

More details here.

MPEG-4 SLS is not really news, but Fraunhofer finally seems to be pushing this out to a broader public now. Decoders are supposed to be ready within 12 weeks for literally all current (mobile and stationary) hardware platforms.

Seems to be a great product, I hope Apple picks this up!

It's probably not necessarily better than other hybrid solutions. But it would be nice if it got enough momentum to be implemented into the top line of mobile players and their ecosystems. For example, if you would be able buy HD-AAC in the iTMS and then let it copy just the AAC-LC part to your iPod.

This post has been edited by rpp3po: Jan 10 2010, 22:35

[mixminus1]

For example, if you would be able buy HD-AAC in the iTMS and then let it copy just the AAC-LC part to your iPod.

...or just buy ALAC files and then have iTunes encode to AAC on-the-fly when you sync your iPod (like it already can do with the shuffle).

This would seem to be the simpler solution as it utilizes an existing format, allows the end user to choose the AAC bitrate, and should also be more efficient from a downloading and storage standpoint (assuming the HD-AAC files would be larger than ALAC due to their hybrid nature).

[C.R.Helmrich]

This would seem to be the simpler solution as it utilizes an existing format, allows the end user to choose the AAC bitrate, and should also be more efficient from a downloading and storage standpoint (assuming the HD-AAC files would be larger than ALAC due to their hybrid nature).

I heard/read somewhere that the compression performance of HD-AAC is supposed to be on par with FLAC and similar dedicated lossless coders.

Chris

[Garf]

I heard/read somewhere that the compression performance of HD-AAC is supposed to be on par with FLAC and similar dedicated lossless coders.

Chris

If we don't include speed into the comparison. But yes, compression ratio is OK. One can wonder what the use of MPEG4 ALS is once you have SLS.

MPEG4 SLS (HD-AAC) will win if you need to transcode, because it only needs minimal processing to "slice" the stream to the bitrate you want, and the AAC or AAC+SLS layers are backwards compatible to LC-AAC.

[mixminus1]

MPEG4 SLS (HD-AAC) will win if you need to transcode, because it only needs minimal processing to "slice" the stream to the bitrate you want, and the AAC or AAC+SLS layers are backwards compatible to LC-AAC.

Ah, didn't get that part from the block diagram in the Fraunhofer PDF.

So you can take an HD-AAC file, choose to "slice" it to 256 kb/sec or 128 kb/sec, and either of those resulting files would be playable by any device capable of LC-AAC playback?

[rpp3po]

Both the HD-AAC and the sliced LC-AAC file can be played back on a legacy device. The LC-AAC portion of the HD-AAC file is only encoded once, though. So you can only slice a new file out at the bitrate that was originally encoded, e. g. 256 kbit/s. For other bitrates you need to re-encode the lossless data.

This post has been edited by rpp3po: Jan 11 2010, 17:22

[Garf]

Both the HD-AAC and the sliced LC-AAC file can be played back on a legacy device. The LC-AAC portion of the HD-AAC file is only encoded once, though. So you can only slice a new file out at the bitrate that was originally encoded, e. g. 256 kbit/s. For other bitrates you need to re-encode the lossless data.

To clarify, you can only slice out a new file at a higher bitrate than what the LC-AAC part was originally encoded with. So applications of HD-AAC would generally encode the LC-AAC at something lower like 96 or 128kbps, rather than a higher bitrate.

If the LC-AAC part of the file was encoded at 128kbps, you can still slice out a 256kbps HD-AAC file, which would be 128kbps LC-AAC plus 128kbps correction layer. The correction layer is very efficient and the combination could reasonably be compared to a 256kbps LC-AAC file.

The resulting file will play back as a 256kbps file in a HD-AAC player and like 128kbps in a LC-AAC player.

I hope this made it clearer instead of the other way around

[mixminus1]

Yep, got it, thanks!