Issue when adding a title to an audio stream within a mp4 file

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Issue when adding a title to an audio stream within a mp4 file

PPRJ01
Hello All,

I'm not a developper. Therefore I'm not able to analyze the ffmpeg/ffprobe source code.

I observed that the command below seem to work properly when adding a title to an audio stream within an MP4 file :

      ffmpeg -i INPUT.mp4 -c copy -metadata:s:a:0 "title=mono" OUTPUT.mp4

Both VLC and Exiftool do display correctly the audio stream title of the OUTPUT.mp4 file when needed.

The point is that neither ffmpeg nor ffprobe can do it.

For example, the command : ffmpeg -i OUTPUT.mp4 (with no output file) do not show the audio title.

I don't know where ffmpeg stores the title metadata but VLC and Exiftool are able to retrieve it.

Maybe this is a designed behavior of ffmpeg/ffprobe.

Or a bug ?

Please let me know.
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Re: Issue when adding a title to an audio stream within a mp4 file

Moritz Barsnick
On Wed, Feb 24, 2021 at 17:37:18 +0100, PPRJ01 wrote:
> I observed that the command below seem to work properly when adding a title to an audio stream within an MP4 file :
>
>       ffmpeg -i INPUT.mp4 -c copy -metadata:s:a:0 "title=mono" OUTPUT.mp4
>
> Both VLC and Exiftool do display correctly the audio stream title of the OUTPUT.mp4 file when needed.
>
> The point is that neither ffmpeg nor ffprobe can do it.

Indeed, I can confirm this. ffmpeg is able to insert the per-track
"title", but not able to extract it.

(Technical detail: it's the "name" atom beneath the "udta" atom beneath
the "trck" atom.)

> Maybe this is a designed behavior of ffmpeg/ffprobe.
> Or a bug ?

A shortcoming.

I'm able to change the ffmpeg source code to parse the per-track title,
but cannot get it inserted properly in the demuxer metadata.

Moritz
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Re: Issue when adding a title to an audio stream within a mp4 file

PPRJ01
Thank you Moritz. I really apreciate your kind answer.

But ... I don't understand what you are planning to do.

Please tell me if I'm right or wrong :

- ffprobe/ffmpeg will display the data contained in the "name" atom to stdout/stderr
BUT
- ffmpeg will NOT be able to copy the audio stream "title" to a new MP4 output file by using the -c copy option

Please let me know.

Pascal
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Re: Issue when adding a title to an audio stream within a mp4 file

Moritz Barsnick
On Mon, Mar 01, 2021 at 15:17:40 +0100, PPRJ01 wrote:
> But ... I don't understand what you are planning to do.

I'm not planning to do anything. I checked whether this could easily be
fixed, but it cannot with my knowledge.

> Please tell me if I'm right or wrong :
> - ffprobe/ffmpeg will display the data contained in the "name" atom to stdout/stderr

No. When reading a file, ffmpeg does not understand it.

> BUT
> - ffmpeg will NOT be able to copy the audio stream "title" to a new MP4 output file by using the -c copy option

Correct, ffmpeg does not understand your title when reading, and can
therefore also not convey it to an output file.

An ffmpeg developer, especially one who knows their way around atoms,
might be able to fix this. (I can give more details what my issues
were, if anyone picks this up.)

Moritz
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