Format of BBC Radio 4 .m4a files

RS richard22j at
Wed Sep 9 03:05:09 PDT 2015

Does anyone know what software the BBC uses to encode its .m4a files?  I am 
unable to play them on an AGPtek Longevity player, which says it supports 
AAC-LC.  If I let get_iplayer default to flashaacstd, I get .m4a files with 
a bit rate of 128kbit/s and a sample rate of 44.1kHz or 48kHz (depending on 
the programme).  If I play them in VLC and look at Tools Codec no AAC 
extensions are shown, so they must be AAC-LC files.  Anyway this forum 
thread says an AAC-LC player should ignore SBR and PS information in HE-AAC 
If I try to play the BBC Radio 4 .m4a files in the Longevity player the 
player freezes for about 4min.

Leo at AGPtek support has been very helpful.  He has referred me to this 
test page.
Many of the files there have a .m4a container and the player will play them, 
so the container does not seem to be an issue.  It will even play the 
MediaCoder Test 1 and Test 6 files which are respectively HE-AAC v1 with SBR 
and HE-AAC v2 with SBR and PS.

I have also tried using flashaaclow which gives a bit rate of 48kbit/s and a 
sample rate of 24kHz.  The player will play the resultant .m4a file which is 
HE-AAC v1 with SBR, but it takes about 2min to play a 24min programme.  It 
plays about 6 words, skips and plays another 6 words and carries on like 
that to the end of the programme.

I did have another portable player until it died after two months.  It was a 
GMYLE DAB+ radio and .mp3 player.  It would play .m4a files, but I would get 
a burbling noise every 30s or so.  If I converted the files to .mp3 they 
would play without the noise.  Curiously when I recorded a Polish DAB+ 
channel as .m4a the player played the recording without problem.

Obviously one solution is to convert the .m4a files to .mp3 because they 
then play fine.  On 31 May I asked about the --aactomp3 option.  (Belated 
thanks to everyone who replied.)  I was told I would get better quality if I 
left the files as aac/.m4a than if I converted them to .mp3.  It does not 
seem to be that easy to find a portable player to play the .m4a files.

Any suggestions? 

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