Does Rockbox support mp4 (aac) audio on the Sansa e200 series?

[cocopugg]

I just came across some mp4 (aac) songs and tried to play them on my Sansa, but they were playing sped up and skipping. Does Rockbox have a plugin that I'm not aware of to play mp4 on the Sansa? I've searched the forums but couldn't find the answer. Thanks to the Rockbox team for their great work!

[Lear]

Sped up and skipping? Sounds like it could be HE-AAC, but not correctly identified as such. The speed thing could probably be fixed, but not the skipping, as the Sansa CPU isn't powerful enough (at least with the decoder we use).

[cocopugg]

Thanks for your reply Lear. Is their a plugin I can try to see if it plays the files correctly? Thanks again.

[saratoga]

You could load then in foobar2000 and check their properties.  If they say AAC+/AAC+v2/AAC-HE/AAC-PS then they can't be played on your Sansa due to lack of CPU speed.

[cocopugg]

You could load then in foobar2000 and check their properties.  If they say AAC+/AAC+v2/AAC-HE/AAC-PS then they can't be played on your Sansa due to lack of CPU speed.

Thanks Saratoga. I did just as you asked. Here is what it says in properties:
Sample Rates: 44100 Hz
Channels: 2
Codec: AAC
Codec Profile:AAC SBR
Bitrate 192kbps

[saratoga]

You could load then in foobar2000 and check their properties.  If they say AAC+/AAC+v2/AAC-HE/AAC-PS then they can't be played on your Sansa due to lack of CPU speed.

Thanks Saratoga. I did just as you asked. Here is what it says in properties:
Sample Rates: 44100 Hz
Channels: 2
Codec: AAC
Codec Profile:AAC SBR
Bitrate 192kbps

SBR is means AAC-HE, which means you'll need a much faster CPU then the Sansa has.  

Also, I don't know where you got that file from, but using 192kbps w/ SBR makes no sense.  SBR decreases quality above 80kbps, and requires 2-3x more CPU time then regular AAC (AAC-LC).  It really should only be used around 64kbps, and even then I'm not sure it makes sense given the huge CPU time and modest compression gains.  

[cocopugg]

Thanks Saratoga, I'll just scrap those files. I hope I didn't do any damage to the CPU by trying to play it.

[Elbart]

SBR is means AAC-HE, which means you'll need a much faster CPU then the Sansa has.

Sorry for reviving this old thread, but does that mean the e200-series will never be capable of playing HE-AAC files or is it a matter of codec-optimization?

[Chronon]

I highly doubt it.

Here's a wiki page listing some decoding times for various codecs -- test files all generated from a single source file.  The Gigabeat can handle HE-AAC okay, but it doesn't look like any of the other listed targets come close to real time.  Unfortunately the person who tested a Sansa did not try HE-AAC, so we don't have a benchmark for that.  

Interestingly, it looks like Rockbox does better with HEv2-AAC compared with HE-AAC.  

[Elbart]

I'm going to compile the latest build with the test_codec app and test a few aac-files.

EDIT: I'm using the sample from here.

Code: [Select]

nero_096.m4a          Decode time -  93.20s   188.79% realtime
nero_128.m4a          Decode time -  97.36s   180.73% realtime
nero_192.m4a          Decode time - 103.41s   170.15% realtime
nero_256.m4a          Decode time - 107.65s   163.45% realtime
nero_320.m4a          Decode time - 113.57s   154.93% realtime
nero_400.m4a          Decode time - 119.60s   147.12% realtime
nero_q0.3_(he).m4a    Decode time - 312.55s    56.31% realtime
nero_q0.2_(he).m4a    Decode time - 318.22s    55.31% realtime
nero_q0.1_(hev2).m4a  Decode time - 350.45s    50.22% realtime

I don't know, how much CPU-Time PS and SBR respectively need, but the impact of SBR is pretty hard, especially since the average bitrate of the q0.3 file is 86kbps, whereas the 096 file has an average bitrate of 90. q0.4 results in a LC file with an averave bitrate of around 100.

I used the August 2007 build of the Nero AAC Encoder and b16698 of Rockbox with the test_codec-modification.