Rockbox Technical Forums

Support and General Use => Audio Playback, Database and Playlists => Topic started by: BZFrank on April 27, 2016, 08:15:21 PM

Title: Playing raw AAC without transcoding
Post by: BZFrank on April 27, 2016, 08:15:21 PM
Howdy,

this is something is stumbled upon while trying to get a bunch of AAC files (extracted as stream from videos) to play in Rockbox on a Sansa Clip+. The plain AAC files are not shown and renaming them to m4a or mp4 does not work either as Rockbox refuses to play them.

I didn't want to transcode the AAC data to something else (due to loss of quality) so I used MP4Box to mux the AAC into an MP4 container.

mp4box -add in.acc -new out.mp4

Now Rockbox plays them without any issues and I am a happy camper.

https://gpac.wp.mines-telecom.fr/mp4box

Of course this is not exactly rocket science but I have seen quite a number of questions about this topic while looking for a solution, so I hope this is useful for anyone seeking wisdom. ;)
Title: Re: Playing raw AAC without transcoding
Post by: saratoga on April 27, 2016, 08:27:52 PM
Yeah, raw AAC is not supported.  It has to be MP4/M4A. 
Title: Re: Playing raw AAC without transcoding
Post by: nmr on June 05, 2016, 11:48:42 PM
This is the exact issue I was having today.

for those wanting to use ffmpeg you can do the same thing like this:

ffmpeg -i input.aac -acodec copy output.mp4
Title: Re: Playing raw AAC without transcoding
Post by: scarf on April 10, 2019, 03:04:08 AM
This didn't work with ffmpeg.  Although Rockbox tries to play the m4a file, it freezes up every few seconds and needs a hard reset.
Also didn't work with mp4box, same thing happens... not sure what is different here compared to OP.  The AAC files are output by streamripper from local radio station.  ffmpeg identifies the input files as HE-AAC and so does Rockbox with the output.  Using a Sansa e280... maybe it isn't fast enough to play the mp4?

Any other ideas on how to get these files playing with as little processing/transcoding as possible (using linux tools)?
Title: Re: Playing raw AAC without transcoding
Post by: saratoga on April 10, 2019, 09:02:28 AM
The e280v1 is not fast enough to play aac-he. The v2 is fast enough, but it sounds like you have the v1.
Title: Re: Playing raw AAC without transcoding
Post by: scarf on April 11, 2019, 01:51:52 AM
OK thanks, probably right... how could I tell which version it is?
Also what would be the best way to make these files playable with least possible quality loss?  I opened up the aac file in Audacity and took a look at the spectrogram, looks like it's about 34 kHz.  I tried transcoding it to mp3 q9 (worst) and it cut the audio way down to 22 kHz and doubled the file size  :'(
Ogg q0 (worst) was better, cutting it to 30 kHz and increasing the file size by 50%.... any other ideas?  thanks
Title: Re: Playing raw AAC without transcoding
Post by: saratoga on April 11, 2019, 12:39:15 PM
Normal hearing only goes up to 16 KHz, so there shouldn't be higher frequencies in normal audio. 

I would convert the files to Ogg or regular AAC. 
Title: Re: Playing raw AAC without transcoding
Post by: scarf on April 11, 2019, 01:59:09 PM
Well yeah, I was looking at the total frequency of the file, so a 30 kHz Ogg file with 2 channels would be 15 kHz for each channel (ear), so it should be pretty OK. 

but your statement reminds me of something quite interesting.  Research has been done that instruments can produce frequencies over 100 kHz and, even though we don't hear these frequencies, they still have an effect on the tiny bones in our inner ear and our bodies, contributing to the overall "listening experience"... but short of a live concert, would need top-notch recordings and audio-reproduction equipment to re-experience the frequencies.   But cutting out those frequencies does have effects... something to think about.
https://www.cco.caltech.edu/~boyk/spectra/spectra.htm

But for listening in the car, the Ogg looks like the best bet.  AAC produces the cleanest copy but the file size more than quadruples!