MP2 audio stream in MP4 container is recognized as MP3

[Nomis101]

Summary of the bug:
An MP4 file that contains an MP2 audio stream is incorrectly recognized as MP3 stream. Mediainfo recognizes the same stream as "MPEG Audio (Version 1) (Layer 2)" and VLC as "MPEG Audio Layer 1/2 (mpga)".

How to reproduce:
I have an MKV file that contains MP2 audio. I converted this into MP4.

% ffmpeg -i /Volumes/Developer/Testfile.mkv -c copy /Volumes/Developer/Testfile.mp4
ffmpeg version N-98021-g2a9ffd89fc Copyright (c) 2000-2020 the FFmpeg developers

built with Apple clang version 11.0.3 (clang-1103.0.32.62)
configuration: --pkg-config-flags=--static --enable-swscale --enable-avfilter --enable-fontconfig --enable-gpl --enable-version3 --enable-libass --enable-libbluray --enable-libfreetype --enable-libsoxr --enable-libaom --enable-libmp3lame --enable-librav1e --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libwavpack --disable-debug --enable-libmysofa --enable-libx264 --enable-libx265 --enable-libxvid --enable-nonfree --enable-libfdk-aac --enable-muxer=mov --enable-muxer=mp4 --enable-muxer=ipod --enable-encoder=eac3 --enable-encoder=ac3 --enable-encoder=flac --enable-ffplay --enable-librtmp --enable-libsmbclient --enable-opencl --enable-libssh --enable-openssl --enable-encoder=truehd --enable-bsf=aac_adtstoasc --enable-encoder=h264_videotoolbox --enable-encoder=hevc_videotoolbox --enable-sdl --extra-ldflags=-L/opt/local/lib
libavutil 56. 49.100 / 56. 49.100
libavcodec 58. 90.100 / 58. 90.100
libavformat 58. 44.100 / 58. 44.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 84.100 / 7. 84.100
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100

Input #0, matroska,webm, from '/Volumes/Developer/Testfile.mkv':

Metadata:

title : Elephant's Dream
ENCODER : Lavf58.42.101

Duration: 00:00:03.33, start: 0.000000, bitrate: 9360 kb/s

Stream #0:0(eng): Video: vp9 (Profile 3), yuv444p10le(tv, bt709/unknown/unknown), 1920x1080, SAR 1:1 DAR 16:9, 24 fps, 24 tbr, 1k tbn, 1k tbc (default)
Metadata:

DURATION : 00:00:03.332000000

Stream #0:1(eng): Audio: mp2, 48000 Hz, stereo, s16p, 384 kb/s (default)
Metadata:

ENCODER : Lavc58.82.100 mp2
DURATION : 00:00:03.317000000

Output #0, mp4, to '/Volumes/Developer/Testfile.mp4':

Metadata:

title : Elephant's Dream
encoder : Lavf58.44.100
Stream #0:0(eng): Video: vp9 (Profile 3) (vp09 / 0x39307076), yuv444p10le(tv, bt709/unknown/unknown), 1920x1080 [SAR 1:1 DAR 16:9], q=2-31, 24 fps, 24 tbr, 16k tbn, 1k tbc (default)
Metadata:

DURATION : 00:00:03.332000000

Stream #0:1(eng): Audio: mp2 (mp4a / 0x6134706D), 48000 Hz, stereo, s16p, 384 kb/s (default)
Metadata:

ENCODER : Lavc58.82.100 mp2
DURATION : 00:00:03.317000000

Stream mapping:

Stream #0:0 -> #0:0 (copy)
Stream #0:1 -> #0:1 (copy)

Press [q] to stop, ? for help
frame= 80 fps=0.0 q=-1.0 Lsize= 3808kB time=00:00:03.29 bitrate=9473.1kbits/s speed=38.5x
video:3653kB audio:152kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.081670%

It seems everything went fine. But inspecting the MP4 file with FFmpeg, gives:

% ffmpeg -i /Volumes/Developer/Testfile.mp4
ffmpeg version N-98021-g2a9ffd89fc Copyright (c) 2000-2020 the FFmpeg developers

built with Apple clang version 11.0.3 (clang-1103.0.32.62)
configuration: --pkg-config-flags=--static --enable-swscale --enable-avfilter --enable-fontconfig --enable-gpl --enable-version3 --enable-libass --enable-libbluray --enable-libfreetype --enable-libsoxr --enable-libaom --enable-libmp3lame --enable-librav1e --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libwavpack --disable-debug --enable-libmysofa --enable-libx264 --enable-libx265 --enable-libxvid --enable-nonfree --enable-libfdk-aac --enable-muxer=mov --enable-muxer=mp4 --enable-muxer=ipod --enable-encoder=eac3 --enable-encoder=ac3 --enable-encoder=flac --enable-ffplay --enable-librtmp --enable-libsmbclient --enable-opencl --enable-libssh --enable-openssl --enable-encoder=truehd --enable-bsf=aac_adtstoasc --enable-encoder=h264_videotoolbox --enable-encoder=hevc_videotoolbox --enable-sdl --extra-ldflags=-L/opt/local/lib
libavutil 56. 49.100 / 56. 49.100
libavcodec 58. 90.100 / 58. 90.100
libavformat 58. 44.100 / 58. 44.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 84.100 / 7. 84.100
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Volumes/Developer/Testfile.mp4':

Metadata:

major_brand : isom
minor_version : 512
compatible_brands: isomiso2mp41
title : Elephant's Dream
encoder : Lavf58.44.100

Duration: 00:00:03.33, start: 0.000000, bitrate: 9362 kb/s

Stream #0:0(eng): Video: vp9 (Profile 3) (vp09 / 0x39307076), yuv444p10le(tv, bt709/unknown/unknown), 1920x1080, 8981 kb/s, SAR 1:1 DAR 16:9, 24.01 fps, 24 tbr, 16k tbn, 16k tbc (default)
Metadata:

handler_name : VideoHandler

Stream #0:1(eng): Audio: mp3 (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 384 kb/s (default)
Metadata:

handler_name : SoundHandler

At least one output file must be specified

Now, it tells it is MP3, but it is MP2 audio. I have attached both files.

[Nomis101]

"I have attached both files." is not true, because the attachment was bigger then the upload limit of 2.5 MB.

[Balling]

Replying to Nomis101:

"I have attached both files." is not true, because the attachment was bigger then the upload limit of 2.5 MB.

Lol, then use google drive.