[FFmpeg-user] id3 tags not really removed?

[Rodolfo Medina]

Rodolfo Medina <rodolfo.medina at gmail.com> writes:

> Moritz Barsnick <barsnick at gmx.net> writes:
>
>> On Mon, May 29, 2017 at 18:37:31 -0400, Ron Sparks wrote:
>>> > ... I also tried to remove all the tags with:
>>> >   $ ffmpeg -i input.mp3 -map 0:a -map_metadata -1 -c copy out.mp3
>>> > and then put them again, but the problem remains...
>>> 
>>> I suspect the problem might be that ffmpeg works with the id3v2 tags, 
>>> while your mp3 reader works with the id3v1 tags.
>>
>> I had the same thought, but why would ffmpeg, when remuxing, re-insert
>> the original id3v1 tags? Perhaps they're considered part of the stream,
>> *then* they would survive "-c:a copy".
>>
>> You may want to try adding "-write_id3v1 1", as hinted in the docs:
>> https://www.ffmpeg.org/ffmpeg-formats.html#mp3
>>
>> In both cases, that should either drop the metadata or insert both
>> versions. (I didn't manage to test, because I don't have any tools at
>> hand which expose both/all types of tags in MP3 files. exiftool should
>> manage.)
>>
>> Other suggestion (never confirmed):
>> https://lists.ffmpeg.org/pipermail/ffmpeg-user/2011-June/001365.html
>>
>> Actually, there are so many forms of tags (incl. EXIF), metadata, and
>> so on, that other tools may be much more suitable for such operations.
>>
>> Cheers,
>> Moritz
>>
>> P.S.: I found "-map_metadata -1" on lists and superuser.com, but
>>       neither in the docs nor the wiki. Hmmm.
>
>
> Unfortunately "-write_id3v1 1" seems to have no effect.  I wish I could
> understand what the problem is.  Let input.mp3 be our file.  I do:
>
>  $ ffmpeg -i input.mp3 - c copy -metadata composer="Bach" output.mp3
>  $ mv -vi output.mp3 input.mp3
>
> , then get on my car and the reader reads fine the `composer' tag as `Bach'.
> Then I remember that J. S. Bach had children who were composers as well, get
> off the car, go to the PC and do:
>
>  $ ffmpeg -i input.mp3 - c copy -metadata composer="Bach J. S." output.mp3
>  $ mv -vi output.mp3 input.mp3
>
> .  Then I get back to the car and the reader keeps on reading simply `Bach'
> instead of `Bach J. S.'  I.e., it does not see the change occurred.  Now, you
> listers say that the problem is in that ffmpeg works with id3v2 tags whereas
> my car's mp3 reader does it with id3v1.  But, if so, why does it read them
> correctly the first time they are created and not the second time, when they
> have been changed?  Besides, it seems that sometimes, when the above ffmpeg
> command is repeated many times, at least the change is somewhat by my reader
> finally seen: but only after repeating it at least twice.


Further tests show that changes in tags are actually detected by the reader but
with a delay: in a first moment they are not, then I `play' again with tags
using ffmpeg and then the reader finally reads them...

Rodolfo