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Topic: A few problems with tags when converting FLAC to MP3 (Read 865 times) previous topic - next topic
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A few problems with tags when converting FLAC to MP3

Hi,

I'm currently using Foobar 2.0 (x64) for Windows 11.

When I convert FLAC files to the MP3 format, I've noticed a few problems regarding tags:

- The Grouping tag becomes the Contentgroup tag.
- If I have multiple artists (each in a separate tag), these artists appear combined in a single tag, like this:

artist 1 / artist 2 / artist 3

However, if I convert to Opus, all my tags are preserved.

I've also noticed that, when converting to Opus, Foobar adds two tags: Encoder and Encoder_options. Nothing is added when converting to MP3.

In both conversion profiles (MP3 and Opus), Transfer Metadata is enabled.

Thanks in advance for your help!

Re: A few problems with tags when converting FLAC to MP3

Reply #1 –
As you should know being a long time member, different audio formats have different tag standards. FLAC uses freeform text, MP3 uses ID3v2 tags with defined fields for specific purposes. And to make life non-miserable, foobar2000 maps the different tag fields to human readable standard fields so it can show them in a manageable format.

Your 'Grouping' field gets written to 'TIT1' field in MP3's ID3v2 tag. That is defined as "content group" and it is used for the very same grouping purpose you use it for with the shorter name. Some tag editors, like MP3Tag, shows the field with "Contentgroup" name, but foobar2000 shows it with name "Grouping".

Your multiple artists get written to a single ID3v2 field because that is how the standard works. You would never see that if you used foobar2000 to read the tags back, as foobar will transparently separate the artists back to separate artist entries. Again, this is not a flaw. The specs state that there can be only one artist field in a file and multiple entries are separated with '/'.
You are using a third party tagger that shows you the raw content of the tag field but doesn't interpret to you what the data means.

Opus uses identical free-form text field tagging as FLAC (often called Vorbis Comments). That's why the field mappings you see are identical.

The extra tag fields you see in the encoded Opus files are not written by foobar2000, but by the opus encoder opusenc.exe.

Re: A few problems with tags when converting FLAC to MP3

Reply #2 –
Thanks for the reply!

1. I'm not an expert, but I do know that there are different tag specifications. I just hoped that tags already present in an audio file could be preserved and copied in destination, even if a particular tag actually corresponds to another tag with a different name. It looks like it's more complicated than that, so I'll just accept the facts.

2. I can't remember the technicalities regarding how mp3tag works with multiple tags. What I can say is that, on the main screen, on the Artist field, you get just one line (Artist1\\Artist2\\Artist3), but then, when you click on the list of extended tags, what you see is three different artist tags. I don't know what the standard is, but it works for me on Aimp or Musicbee. Again, if this is the way it works in Foobar, so this is the way it works.

3. As for the extra tags created by opusenc.exe, it's not a big deal to me, but I wonder if it's possible to disable them without having to use command line.

These are tricky issues for me and I do appreciate the help.

Re: A few problems with tags when converting FLAC to MP3

Reply #3 –
Quote from: Vivadavid on
2. I can't remember the technicalities regarding how mp3tag works with multiple tags. What I can say is that, on the main screen, on the Artist field, you get just one line (Artist1\\Artist2\\Artist3), but then, when you click on the list of extended tags, what you see is three different artist tags. I don't know what the standard is, but it works for me on Aimp or Musicbee. Again, if this is the way it works in Foobar, so this is the way it works.
I think Mp3tag uses the ID3v2.4 field separator in ID3v2.3 tags, so whilst foobar is correctly inserting '/' Mp3tag is expecting a NUL separator and is therefore showing 'Artist1 / Artist2 / Artist3' instead of 'Artist1\\Artist2\\Artist3'.

If you can it's best to use ID3v2.4 as that should display correctly everywhere.

Re: A few problems with tags when converting FLAC to MP3

Reply #4 –
Quote from: SimBun on

I think Mp3tag uses the ID3v2.4 field separator in ID3v2.3 tags, so whilst foobar is correctly inserting '/' Mp3tag is expecting a NUL separator and is therefore showing 'Artist1 / Artist2 / Artist3' instead of 'Artist1\\Artist2\\Artist3'.

If you can it's best to use ID3v2.4 as that should display correctly everywhere.

Sorry for not replying earlier and thanks for the information. I tried using Unicode 2.4, but it didn't work for me. In any case, as it's a tricky issue and most of the time I just use Opus, I'll just accept that tagging mp3 files cause certain problems.