USDX does not handle audio files with more than two channels (stereo) correctly (on macOS and Linux).

[bohning]

Actual behaviour

USDX seems to incorrectly handle multi-channel audio files (multi as in more than two channels = stereo), at least on macOS and Linux (but seems to work on Windows).

I have an m4a which contains 6 channels of audio (known as "5.1", "3F2R/LFE" is the info that VLC provides me - meaning "3 front, 2 rear/Low Frequency Effects = bass/subwoofer). When using as audio source via #MP3, USDX plays back the file way faster than it should, so it's not usable. It seems that it tries to squeeze in audio from multiple channels into a timeframe. The playback sound is okay, but the timings are messed up, e.g. the timer is a lot faster than regular time. If there is a video, the video will play with the increased speed.

Expected behaviour

USDX should be able to handle multi-channel audio files, probably by just disregarding the additional channels and using left and right channel for stereo playback.

Steps to reproduce

This 5.1 m4a file can be used together with the following minimal txt to reproduce and debug this issue. The lyrics helper is on steroids, the time display progresses way too fast.

#TITLE:multi-channel bug
#ARTIST:multi-channel bug
#MP3:a-trip-far-far-away_5.1_.m4a
#BPM:400
#GAP:18060
: 0 1 0 
- 1
: 1 1 0 
E

Details

• USDX version: latest main (self-compiled)
• Operating System + version: macOS Sonoma (14.5), Intel (confirmed to also happen on Linux, but doesn't happen on Windows)

[bohning]

I guess the comment here says it all:

USDX/src/media/UAudioDecoder_FFmpeg.pas

Line 444 in 80adde2

// TODO: should we use this or not? Should we allow 5.1 channel audio?

[bohning]

@s09bQ5 Would that be something you could take a look at? Or decide that it's not worth fixing and require a (max) 2-channel audio file?

[s09bQ5]

I'd love to look into this, but I'm quite busy until Sunday.
Can you provide a test file?
How many channels does your playback device have?

[bohning]

There is no rush here whatsoever. I linked a test file above (it's a random 5.1 m4a file). My playback device has 3 channels (center left, center right and subwoofer).