[FFmpeg-user] File metadata in m4a causing player problem?

[Budge]

On 21/10/2019 09:28, Moritz Barsnick wrote:
> Hi Budgie,
> 
> On Sun, Oct 20, 2019 at 09:56:40 +0100, Budge wrote:
>> I have a set of m4a audio files which I can play but on which the
>> progress bar does not work.  If I select anywhere along the progress bar
>> playing starts again from the beginning.
> 
> In which players does seeking not work? In all of them? Which did you
> test?
> 
> How were there files created? Are they arbitrary files, or did you
> create them with ffmpeg?
> 
> Can you provide some of these files?
> 
>> The only difference I can see when using ffprobe to examine the metadata
>> is that files which have a creation_time set have a non functioning
>> progress bar problem.
> 
> That may be a symptom of their creation, but not the actual root cause
> for your issues.
> 
>> What I wish to do is remove the tag:
>> creation_time   : 1970-01-01T00:00:00.000000Z
> 
> ffmpeg certainly didn't create this by itself, but I understand that's
> not what you're trying to say. ;-)
> 
>> I confess using ffmpeg to achieve this, if indeed this is the correct
>> tool, is well beyond my ability and I am seeking help here.
> 
> Even though I don't believe that is the root cause, I was going to explain
> to you how to strip metadata using ffmpeg. But it turns out that, when
> remuxing, ffmpeg doesn't actually copy the creation_time. So all you
> have to do may be:
> 
> $ ffmpeg -i input.m4a -c copy output.m4a
> 
> You can then test the output file.
> 
> The resulting file may also be fixed for other reasons than the
> metadata, e.g. reconstruction of some index or something like that,
> which the original may be missing. (Guessing here - just go try.)
> 
> Hope this helps,
> Moritz
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> 
Hi and very many thanks for the detailed reply.

I obtained the file from BBC using get_iplayer, one of several and years
ago.  I believe the  problem resulted from my poor workmanship when, while
upgrading my workstation, I failed to install AtomicParsley.  (Running
on 64 bit system with openSUSE but cannot recall version.)

As a result the files would not play on the Linn DS until I moved the
moov atom to the start of the file metadata using qt-faststart but
otherwise I believe the tags were intact. The files then played OK but
the progress bar problem was present.

I can let you have samples of good and bad files for comparison but they
are quite big so need your advice how to get them to you.  I can use
Dropbox and send a link if this would be OK.

The problem only occurs with my Linn DS devices.  I am using BubbleDS on
Samsung S6 Android phone as control point and minimserver on Qnap NAS as
media server.

On another player such as a RaspberryPi with Raspbian OS
and IQaudio PiDAC etc and Upmpdcli the progress bar works as it should.

AFAIK get_iplayer uses ffmpeg when downloading but I am not a coder so
cannot comment further.

In the light of your advice above there may be other criteria to examine
in the file as;

None of the files I have which do NOT have the creation_time tag work
perfectly.

Only those files which still have the creation_time tag have a problem with
the Linn DS devices.

Meanwhile I will try your suggestion and report progress.

Many thanks once more.
Regards,
Budge