On 14/07/13 13:37, Vangelis forthnet wrote:
On Sat Jul 13 15:52:02 BST 2013, Budgie wrote:
As usual, a couple of questions.
Is the file format HE-AAC v2 the normal output for a low bit rate
download or is it another, to me, anomaly?
Hello.
Yes, 'flashaaclow' radiomode yields an audio file packaged in an MP4
container
(whose format profile is "Apple audio with iTunes info", hence the .m4a
extention),
which in it contains a raw ADTS (audio data transport stream) .aac file
encoded in
HE-AACv2 as you correctly state; HE-AAC is AAC+SBR, v2 indicates the use of
PS (parametric stereo). The encode uses a VBR with a mean value of 48kbps.
NB that if you come from a non-UK IP, this is the only audio quality
available to you
for National Stations.
If in the UK, the default high quality mode (= flashaac/flashaacstd) is
again an
.m4a file, but the audio stream contained therein is encoded in AAC LC
(no SBR, no PS)
@ 128kbps (320kbps for Radio 3) ABR, that's why it is more compatible
with software/
hardware players.
Depending on the player used, the PS part may be skipped (audio plays in
mono), or both
PS+SBR skipped, in which case audio plays in mono and in very low
quality, since only
half the sampling rate is used.
In my Windows setup I haven't come across a software player that does
not play at least
the AAC part of a HE-AACv2 encode. But hardware players (like your
network player here:
http://www.linn.co.uk/all-products/network-music-players/sneaky-ds
) behave differently; the features list of yours only mentions a
"generic AAC" decoding support,
so it may be expected that it does not support HE-AAC (try a World
Service download) or
HE-AACv2, as you have found out.
On your laptop, any ffmpeg based software player (FFplay, + the ones you
mentioned)
can play fully HE-AACv2 audio streams.
What programme can I use to find out the detailed information of what is
in each .m4a file?
As a generic multimedia file "investigator", you can use the CLI FFprobe,
http://ffmpeg.org/ffprobe.html
which, together with FFplay, is part of the FFmpeg package - if it isn't
available
for your OS, maybe its fork "avprobe" is:
http://libav.org/avprobe.html
As a personal choice though, I'd recommend MediaInfo - it comes both as
a GUI & CLI
and is available for a plethora of OSes, including yours (openSUSE 12.2)
here:
http://mediaarea.net/el/MediaInfo/Download/openSUSE
what would you recommend I run to change
the format of the sound file and to what format?
dinkypumpkin in your answer to you has kindly suggested a recode from
HE-AACv2 -> AAC-LC through FFmpeg (or avconv). If your FFmpeg
is built with support for one of the non-free AAC encoders (libfaac or the
far better libfdk_aac), then I guess it'd be fine,
but the native encoder (-c:a aac -strict -2)
lacks in performance, especially in music parts -
for speech is fine.
If I can humbly share my opinion, I have found that a transcode from
HE-AACv2 @48kbps -> LAME MP3 @ 96kbps (for spoken content) /
112 (or even 128) kbps (for music content) is more than adequate and I
would
propose that, since your SneakyDS does play MP3 files.
Regards.
Vangelis
Hi Vangelis,
I have been working on other stuff and only now return to sort out my
problem files. Would you have time to help some more please?
First question concerns diagnosis of the files which do not play on Linn
device. I do have ffprobe but do not see any mention of HE-AACv2 or
AAC-LC when I run it on a problem file. What I do see is :-
[CODE]
Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo,
fltp, 48 kb/s (default).
[CODE]
I interpret this to mean that I have the downloaded the flashaaclow
version which from your advice I interpret to be the HE-AACv2 encoded
version. Is that correct?
Since I have no idea why I get these files from time to time I assume I
do not have get_iplayer set up correctly so that is cannot download in
this format. First request then is what should I put in my options file
to ensure I only get the higher quality radio options?
Second question is please could you help with ffmpeg command line to
convert these files to files that will play as suggested previously by
dinkypumpkin. I regret my knowledge is not up to doing it without more
help with command options.
Finally I note I could transcode on downloading and save these files as
mp3 files but is it also possible to transcode to flac?
Grateful for any further help when you have time.
Regards,
Budgie
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