Format of BBC Radio 4 .m4a files

Jim web web at
Wed Sep 9 04:28:18 PDT 2015

In article <68D324A8D5C641BF85D17D95E4ECF311 at RJCDESK>, RS
<richard22j at> wrote:
> Does anyone know what software the BBC uses to encode its .m4a files?

for all recent 'radio' files I've checked ffprobe tells me:

aac (LC) (mp4a/0x6134706D) 48000 Hz stereo fltp
Major brand M4A encoder Lav54.20.4 compatable isomiso2

The sample rate is 128kb/s for R4/R4X and 320 kb/s for R3.

>  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).

I've not seen a 44.1k sample rate file for a long time, so unless your
samples are old I'm surprised by that. IIRC The BBC ceased outputting RTMP
44.1k when Audio Factory got going and they killed the old server-side
conversions that the ancient Linux Flash plugin needed to avoid its own
poorer conversions because it can't cope with 48k.

Can't comment on the limitations of foibles of commercial players.

> 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.

Well, I suspect many 'consumer' products are still stuck in the era of mp3.
So you may need to spend time checking out recent HiFi mags, etc, to find
more flexible and capable devices. Which alas probably cost more.

Why not flac?

You may also find it useful to install ffmpeg/ffprobe so you can read the
details of your files.


Armstrong Audio
Audio Misc

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