Flac files return empty sample buffers

[richardmitic]

Seeking to certain positions within certain flac files makes ReadableAudioFile.read() return sample buffers of all zeros.

Here is a file + code that triggers the bug:

sine_stereo_0.flac

from pedalboard.io import AudioFile

with AudioFile(file) as af:
    # read 1 second of audio and assert that it contains reasonable samples
    samples = af.read(int(af.samplerate))
    assert not (samples == 0).all()
    
    # seek to 1.1 seconds
    assert af.seekable
    af.seek(int(1.1 * af.samplerate))

    # read 1 second of audio again and assert that samples are reasonable
    samples = af.read(int(af.samplerate))
    assert not (samples == 0).all()  # this will fail

The file was created by generating a sine wave with ffmpeg and encoding with the flac reference encoder at compression level 0. Compression levels 1 and 2 will produce a file that fails in exactly the same way.

ffmpeg -f lavfi -i "sine=frequency=1000:duration=5" -filter_complex "[0:a][0:a]amerge=inputs=2[aout]" -map "[aout]" sine_stereo.wav
flac -0 sine_stereo.wav -o sine_stereo_0.flac

For comparison, here's a file that can be read without problems. It was created in the same way but uses compression level 3 instead.
sine_stereo_3.flac

flac -3 sine_stereo.wav -o sine_stereo_3.flac

[psobot]

Thank you @richardmitic! I've been able to reproduce this in a test, and local tests so far seem to show that the return code of the FLAC__stream_decoder_seek_absolute method is being ignored, and the return code is often false (meaning there's an error).

I'll try the simplest thing first: bumping JUCE versions, as the newest version of JUCE includes a version bump of the FLAC library itself.

[psobot]

Quick update: I've tracked this down to a very small bit of code in JUCE's FlacReader class and opened an issue. Until that's resolved, I'll see what we can do about fixing the issue within Pedalboard by vendoring the juce::FlacAudioFormat classes and patching out the bug.

[richardmitic]

Excellent work! Thanks for tracking it down.