How to fix id3tag of mp3 files

Preliminary notes:

This post is the sum of many hours of researching the web for solutions, reading for many hours: man, info and community pages. And a lot of testing.

This is a solution for Linux users (probably also good for MacOS too).  MS Windows user, sorry, you need to contact MS support for help.

Part of the following is cut/past form other sources I found on the web.  Thank you for the active community of Linux users like me.

As usually noted, the following is for sharing knowledge only, do it at your own risk!  Make a backup plan before proceeding.

Basic knowledge:

Libavformat (lavf) is a library for dealing with various media container formats.  Its main two purposes are demuxing - i.e. splitting a media file into component streams, and the reverse process of muxing - writing supplied data in a specified container format.

The MP3 muxer writes a raw MP3 stream with the following optional features:

An ID3v2 metadata header at the beginning (enabled by default). Versions 2.3 and 2.4 are supported, the id3v2_version private option controls which one is used (3 or 4).

Setting id3v2_version to "0" disables the ID3v2 header completely.

The muxer usually support writing attached pictures (APIC frames) to the ID3v2 header. The pictures are supplied to the muxer in form of a video stream with a single packet. There can be any number of those streams, each will correspond to a single APIC frame. The stream metadata tags title and comment map to APIC description and picture type respectively.

See http://id3.org/id3v2.4.0-frames for allowed picture types.

Note that the APIC frames must be written at the beginning, so the muxer will buffer the audio frames until it gets all the pictures. It is therefore advised to provide the pictures as soon as possible to avoid excessive buffering.  Also keep picture small (ie. less than 1% of total mp3 size is a good rule/target to follow).

A Xing/LAME frame right after the ID3v2 header (if present). It is enabled by default, but will be written only if the output is seekable. The write_xing private option can be used to disable it. The frame contains various information that may be useful to the decoder, like the audio duration or encoder delay.

A legacy ID3v1 tag at the end of the file (disabled by default). It may be enabled with the write_id3v1 private option, but as its capabilities are very limited, its usage is not recommended.  This is important for old mp3 players that only understand ID3v1 tags.

Examples:

On the next part you must change the input, out.mp3 and cover.png to your own fit.

1) Write an mp3 with an ID3v2.3 header and an ID3v1 footer:

ffmpeg -i input.mp3 -id3v2_version 3 -write_id3v1 1 out.mp3

2) To attach a picture to an mp3 file select both the audio and the picture stream with map:

ffmpeg -i input.mp3 -i cover.png -c copy -map 0 -map 1 \
-metadata:s:v title="Album cover" -metadata:s:v comment="Cover (Front)" out.mp3

3) Write a "clean" MP3 without any extra features:

ffmpeg -i input.wav -write_xing 0 -id3v2_version 0 out.mp3

Let's get work done:
So this is what I did to add a cover image to a mp3 that already had id3tags:

ffmpeg -i orignal.mp3 -i cover.jpg -map 0:0 -map 1:0 -c copy -id3v2_version 3 -metadata:s:v comment="Cover (Front)" final.mp3

Other thoughts:

I did use a jpeg image for the cover and ffmpeg accepted it as well as vlc, mpv and other players I tested did work fine.

So if you need to include the same cover on many files (ie an album) in a folder, you can do this:

1) "cd" to the target folder
2) "mkdir new" in the target folder
3) rename the cover image file to cover.<ext> where <ext> could be png or jpg depends on your choice and particular case, or convert it to jpg.
3) then copy and past the following script (and hit the [ENTER] key):

for file in *.mp3; do ffmpeg -i "${file}" -i cover.jpg \
 -map 0:0 -map 1:0 -c copy -id3v2_version 3 -metadata:s:v \
 comment='Cover (Front)' ./new/"${file}"; done

After it runs you will have a sub-folder with the new mp3 files all with the embedded cover image you inserted with the script.

Have fun!  Cheers!