Opus Reported Sample Rate

[DistinctBee]

FileProperties of opus files report the input sample rate instead of the actual one as sample rate. This is a behavior different to other formats in lofty, e.g. its sister format vorbis.

I'm mainly interested to know: was this fully intentional and were side effects like an opus file being able to be declared 192kHz (which opus does not support) accepted?

I could not find anything on this in code or documentation and no issues mentioning it.

I compared this to tablib, which returns a constant 48kHz (which is a valid interpretation of opus' slightly unusual relationship to sample rate), with inputSampleRate kept as a separate information.

I also experimentally compared¹ behavior of ffmpeg and opusenc as established encoder software on this matter, showing that ffmpeg declares the closest opus-supported playback rate as input, while opusenc seems to stick to the RFC by handing down the actual source value.

Footnotes

1. experiment shell script ↩