Audio distortion on playback of lower bitrate files

[sunhay]

I'm working on a toy resource-viewer for a well known game and I have a set of mp3s (BGM) that I'm trying to play using go-mp3 + oto which all have audible distortion. ffplay is able to play them all just fine.

I'm running on MacOS Catalina (10.15.6).

ffmpeg -i 01.mp3
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 11.0.3 (clang-1103.0.32.62)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, mp3, from '01.mp3':
  Metadata:
    encoder         : Lavf58.45.100
  Duration: 00:01:14.66, start: 0.023991, bitrate: 80 kb/s
    Stream #0:0: Audio: mp3, 22050 Hz, stereo, fltp, 80 kb/s

It plays fine when I re-encoded it with libmp3lame at a higher bitrate via: fmpeg -i 01.mp3 -codec:a libmp3lame -qscale:a 2 output.mp3, and re-encoding (with libmp3lame again) it again at a low bitrate causes the issues to reappear.

Relevant playback code on my side:

        ...
        d, err := mp3.NewDecoder(bytes.NewBuffer(b))
	if err != nil {
		return err
	}

	c, err := oto.NewContext(d.SampleRate(), 2, 2, 4096)
	if err != nil {
		return err
	}
        ...

Any tips on what the issue might be given that these play fine on other mp3 players? Tuning the sample rate and buffer size in bytes parameters have not helped.

I've uploaded the file here if you'd like to take a look.

[sunhay]

Ah - this might be because MPEG2 is not fully supported yet, per the description in: https://github.com/hajimehoshi/go-mp3/pull/35

[sunhay]

Just an update: it might be stereo intensity related per the above PR description and some very light debug logging that I added. I'll see if I can figure out how to fix it

[bloeys]

Hey any news on this? There are still distortions when playing lower frequency files. Re-encoding to 44100 works perfectly but I was hoping for low frequency support too.