AAC in M4A container: can it be transcoded from remote source (http)?

[mherger]

I think this is something which has been bugging me in the past: can I transcode AAC in a M4A container to FLAC/MP3 if it's streamed over http? It's not a radio station, but files with a well defined length.

TIDAL is going to drop support for mp3. Which means we'll no longer be able to play the basic (lossy) quality on older hardware :-(

[bpa]

I think this is something which has been bugging me in the past: can I transcode AAC in a M4A container to FLAC/MP3 if it's streamed over http? It's not a radio station, but files with a well defined length.

TIDAL is going to drop support for mp3. Which means we'll no longer be able to play the basic (lossy) quality on older hardware :-(

How is this different to playing a m4a podcast ?

[mherger]

> How is this different to playing a m4a podcast ?

I don't think it is. Can those be transcoded?

--

Michael

[bpa]

> How is this different to playing a m4a podcast ?

I don't think it is. Can those be transcoded?

EXample of m4a podscast http://radiofrance-podcast.net/podcast09/rss_12283.xml
They play OK now on my SB3 but I use a ffmpeg - problem is you can skip to a time point.

I had been looking at taking the MPEG4/AAC code stuff from BBCiPlayer and make an all Perl transcoder for MPEG4-AAC which would then deal with timepoints.

mp4 mp3 * *
        # R:{BITRATE=-B %B}T:{START=-ss %s}
        [ffmpeg] -loglevel quiet  -f mp4 -i $FILE$ -f wav - | [lame] --silent -q $QUALITY$ $BITRATE$ - -

mp4 pcm * *
        # R:{BITRATE=-B %B}T:{START=-ss %s}
        [ffmpeg] -loglevel quiet  -f mp4 -i $FILE$ -f s16le -

mp4 flc * *
        # R:{BITRATE=-B %B}T:{START=-ss %s}
        [ffmpeg] -loglevel quiet -f mp4 $START$ -i $FILE$ -f flac -

.

[bpa]

I have a niggling idea that the above solution may break some playing m4a files on either players which can or cannot play AAC natively - but not absolutely sure .

[mherger]

> They play OK now on my SB3 but I use a ffmpeg - problem is you can skip

I was wondering whether we should switch to using ffmpeg at some
point... I know that some LMS "reseller" have modified their version of
LMS to use it exclusively for all kinds of transcodings.


--

Michael

[bpa]

> They play OK now on my SB3 but I use a ffmpeg - problem is you can skip

I was wondering whether we should switch to using ffmpeg at some
point... I know that some LMS "reseller" have modified their version of
LMS to use it exclusively for all kinds of transcodings.

faad is "lean and mean" - small memory and disk space footprint and quick to start.

ffmpeg is big and there many build options so maybe more maintenance effort required. However it is very flexible and capable. Not sure if the problem of skipping to a time point/chapters will be fully handled - also

However, I think using ffmpeg to handle protocol and not codec issues ends up with unnecessary transcoding of AAC to Flac and sending Flac to a player which is capable of playing AAC - so more CPU & Network usage.

I prefer the result of my PlayHLS which uses Perl to handle HLS (e.g. MPEG2-ts) and then send AAC into LMS which then decides to forward unchanged to player or transcoded with full metadata (i.e. metadata is taken from input stream either ID3 or MEPG2-ts and sent to player).

ffmpeg is good for the quick and dirty support of a new format/protocol but it is usually a compromise with longer term maintenance issues and possible reduced functionality (e.g. time points, chapters, metadata) .

[mherger]

> However, I think using ffmpeg to handle protocol and not codec issues
> ends up with unnecessary transcoding of AAC to Flac and sending Flac to
> a player which is capable of playing AAC - so more CPU & Network usage.

But do you believe there could be a Perl solution to the transcoding of
online AAC to something else? It's a part of LMS you know much better
than I do :-).

--

Michael

[philippe_44]

> However, I think using ffmpeg to handle protocol and not codec issues
> ends up with unnecessary transcoding of AAC to Flac and sending Flac to
> a player which is capable of playing AAC - so more CPU & Network usage.

But do you believe there could be a Perl solution to the transcoding of
online AAC to something else? It's a part of LMS you know much better
than I do :-).

--

Michael

I’m late to the discussion (and slow) but why do you want to transcode?

[mherger]

> I’m late to the discussion (and slow) but why do you want to transcode?

Because the ip3k based players (SB3/Receiver/Boom/Transporter) don't
support AAC.

No problem for the Transporter user, of course, because he'll certainly
pay the premium to stream TIDAL in FLAC :-).

--

Michael