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Bug 1954: Clicks may occur starting/pausing play-at-speed or Scrub

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Problem:
On Windows, after 50ms, there is a short period of roughly zero introduced into the output. On Linux, there is also a spike which sounds like a crackle.

In AudioIO::FillBuffers(), Mixer::SetTimesAndSpeed() is called, which sets mT0 and mT1 to a small interval.
In Mixer::MixVariableRates(), all the samples in the interval are used, which means the Resample::Process() is called with last equal to true.
So when Mixer::MixVariableRates() is called again, the resampler is being reused after a call to Process() in which last is true.
It is not stated in the soxr documentation if the resampler will produce valid results in this case, and it's only the scrubbing code which does this.
I think this is the problem, and so the partial fix below avoids this happening.

Partial fix for play-at-speed and keyboard scrubbing:
For these, there is no need to reset the values of mT0 and mT1. (There is no need to allow for the sample position being used to potentially jump around.)
So for these cases, Mixer::SetSpeed() is called, rather than Mixer::SetTimesAndSpeed().
This commit is contained in:
David Bailes
2020-01-15 11:12:40 +00:00
parent f11b2b6bab
commit 6b9c8e79cc
6 changed files with 32 additions and 8 deletions
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4
src/AudioIOBase.h
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@@ -49,6 +49,7 @@ struct ScrubbingOptions {
bool bySpeed {};
bool isPlayingAtSpeed{};
bool isKeyboardScrubbing{};
double delay {};
@@ -358,6 +359,7 @@ protected:
#ifdef EXPERIMENTAL_SCRUBBING_SUPPORT
PLAY_SCRUB,
PLAY_AT_SPEED, // a version of PLAY_SCRUB.
PLAY_KEYBOARD_SCRUB,
#endif
} mPlayMode { PLAY_STRAIGHT };
double mCutPreviewGapStart;
@@ -411,7 +413,7 @@ protected:
bool PlayingStraight() const { return mPlayMode == PLAY_STRAIGHT; }
bool Looping() const { return mPlayMode == PLAY_LOOPED; }
bool Scrubbing() const { return mPlayMode == PLAY_SCRUB; }
bool Scrubbing() const { return mPlayMode == PLAY_SCRUB || mPlayMode == PLAY_KEYBOARD_SCRUB; }
bool PlayingAtSpeed() const { return mPlayMode == PLAY_AT_SPEED; }
bool Interactive() const { return Scrubbing() || PlayingAtSpeed(); }