Problems with interpreting certain AAC/M4B files

[Kassius]

Hi all

I have been using Rockbox on my iPod for audiobook for some time now and it works great with various codecs, including AAC.

I get most of the audiobook from Audible, and Rockbox plays the high resolution 125kbps/44100Hz M4Bs just fine, but with the lower resolutions 62k/22050Hz, the screen starts to freeze and the codec and sample rate shown is wrong. All the are AACs are low complexity, but according to Rockbox the 62k/22050Hz are AAC high efficiency and have a sample rate of 44100 hertz.

I have the same problem with the 32k/22050 though they are playable (due to the lower resolution I assume).

Any suggestions to what might be causing the problem and how to fix it?

For now I convert them to flac (to retain audio quality and because it transcodes faster than opus for instance)

Thank you in advance

[saratoga]

The older iPods are too slow to play AAC-HE files. We didn't disable decoding the HE part like Apple does since for a while it looked like it might be possible to decode with more optimization although maybe we should.

If there's an option for regular AAC, just use that.

[bahus]

codec and sample rate shown is wrong

Is it reproducible on latest  daily build?

https://gerrit.rockbox.org/r/c/rockbox/+/5335 can either be the fix or the cause of this issue.

[Kassius]

Yes, it is the latest daily build and the files are not HE despite what Rockbox thinks.

[Kassius]

I tried the stable build that does not include the https://gerrit.rockbox.org/r/c/rockbox/+/5335 as far as I can see, but the issue seemed to be the same.

[bahus]

I might look into it if you can share problematic file.

[Kassius]

The problem is the same with every 22kHz AAC from Audible I have tried, but not the files I encoded myself with ffmpeg (same settings). How do I share an audio file here? No audio file extensions are allowed..

[Kassius]

Here is a sample, just rename it to M4B after downloading and it should be alright (probably should have zipped it before uploading). https://drive.google.com/file/d/1Dx95hxXadl8BaBmpBoX7SQlwoIKr2D9d/view?usp=drive_link Thank you for taking the time to look at it

[bahus]

This file works properly on my device (Sansa Clip Zip). From what I see file contains implicit SBR signaling which means it's AAC-HE file that's backward compatible with AAC-LC format (can be played both as hi quality 44100 HZ and lower quality 22050 HZ)
SBR decoding is enabled on your device (seems enabled for all devices) but your device is not powerful enough.

SBR decoding (see SBR_DEC) should be disabled for not capable devices. It should fix the issue with backward compatible files.

[bahus]

I prepared test Ipod Video build with SBR decoding disabled. Can you test it?

Ipod Video build:
https://mega.nz/file/9HQklTzB#KnvWhI-6swZe-I6XaaqQTXJWRjnqFUiBtW4RZkKB5Lc

Sources: https://github.com/bahusoid/rockbox/tree/ipodVideoDisableSBR_DEC

[saratoga]

Not sure about audible, but there's usually an option to select download format. Since your device can't decode AAC-HE files, it would make sense to download a supported format like regular AAC or MP3. Disabling SBR decoding will enable decoding, but at lower quality since the SBR part of the file will be ignored

[Kassius]

Thank you very much. The custom build works and the iPod 5G is now playing my audiobook without throttling! As for sound quality I don't hear a difference and even if there is any it not going to be a big problem for speech.

You wouldn't happen to have a script or something to make the building easier when I want a new update?

[saratoga]

I prepared test Ipod Video build with SBR decoding disabled. Can you test it?

Ipod Video build:
https://mega.nz/file/9HQklTzB#KnvWhI-6swZe-I6XaaqQTXJWRjnqFUiBtW4RZkKB5Lc

Sources: https://github.com/bahusoid/rockbox/tree/ipodVideoDisableSBR_DEC

I think this could be committed although it should check for CPU_PP, not just the faster PP models, since it they don't work the slower ones won't either.

[bahus]

I think this could be committed although it should check for CPU_PP

What about PP6100. It looks powerful enough looking at Sansa View CPU frequency (250000000 for sansa vs 11289600 for ipod video). PP6100 seems a dead port but anyway I excluded only PP5002 - PP5022.

Change request: https://gerrit.rockbox.org/r/c/rockbox/+/5548

[saratoga]

If there's ever a PP6100 device that can play music they can test and see if SBR runs in relatively time.