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Fix audio resampling functionality #7858

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@sakertooth sakertooth commented Apr 22, 2025

This PR improves the usage of libsamplerate when resampling.

Changes:

  • Redirect all libsamplerate usage to AudioResampler. This ensures we are always using libsamplerate with the same resampling logic, preventing bugs.

  • Call src_process as many times as necessary to resample all of the source audio we need to fill up the destination buffer. Before, LMMS was only calling src_process once, and assumed that libsamplerate always read all of the input data it gave it, which isn't necessarily true and can cause input frames to be dropped. Any input frames not read in the current iteration are stored within a small array in AudioResampler and will be used on the next call to src_process.

  • Remove the use of buffer margins. This was needed to accommodate for libsamplerate's transport delay, but this involved expensive copies and allocations, and the margin added may not be adequate depending on how long the transport delay needs to be, which wasn't accounted for. To fix this, we allow the transport delay to occur on the onset of when AudioResampler is first used, which then the delay will be removed on subsequent resampling.

@sakertooth sakertooth marked this pull request as draft April 22, 2025 17:31
@sakertooth sakertooth marked this pull request as ready for review April 23, 2025 00:24
@sakertooth sakertooth changed the title Improve correctness of AudioResampler Fix audio resampling logic Apr 23, 2025
@sakertooth sakertooth marked this pull request as draft April 24, 2025 13:39
@sakertooth sakertooth marked this pull request as ready for review April 27, 2025 10:54
@sakertooth sakertooth marked this pull request as draft June 12, 2025 11:37
@sakertooth sakertooth marked this pull request as ready for review June 13, 2025 00:37
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Quick review

@sakertooth
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Appreciate the review 👍

@sakertooth
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Keeping some of the review unresolved because I consider them to bring up outstanding issues we should eventually resolve, maybe before merge.

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Pretty much done

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4 participants