In the file qavaudioframe.cpp there is a function named QAVAudioFrame::data().
It uses the resampler swr_convert() (from swresample.h) in case the input stream's features (channel count, sample rate or format) does not match the desired output format (as returned by QAVAudioFrame::format()).
If this is the case, the bool needsConvert is true and then it is checked whether a (new) instance of the resampler need to be created, by calling swr_alloc_set_opts(). Usually this happens only once when a playback is started, and subsequent calls to swr_convert() does the actual resampling. It is important the instance stays alive for proper resampling.
But because the resampler-state variables d->swr_ctx, d->inSampleRate and d->outAudioFormat are members of the current QAVAudioFrame, this essential resampler-state data is not available anymore on the next cycle, when the next QAVAudioFrame arrives. As a result swr_alloc_set_opts() is called again and again, and proper resampling of the audio fails...
Solution:
I think that the variables swr_ctx, inSampleRate and outAudioFormat should be part of QAVAudioOutputPrivate instead, where housekeeping is done per audio output. After all, each (imagine you have more than one) output device -- or any other samples-consumer -- have different needs.
My quick and dirty fix:
QAVAudioFrame::data() is called from QAVAudioOutputPrivate::readData().
This struct is a member of QAVAudioOutputPrivate and I pass a reference to my slightly modified QAVAudioFrame::data() --> QAVAudioFrame::data(resampler_context_t & resampler_context).
Now, resampler_context is used to store the resampler-state so it won't get lost. Now swr_alloc_set_opts() is called once with the desired parameters and after that, on every next call, the same instance of the resampler is used and resampling works well.
Like I said, my solution is really an ugly patch. Notice that I use a void-pointer as QAVAudioOutputPrivate doesn't need to know what SwrContext looks like. There must be a cleaner way that follows the design of QtAVPlayer.
Finally, there is a strange line in the code where outCount is calculated.
This line should simply be: int outCount = frame->nb_samples;av_samples_get_buffer_size takes care of the math to calculate the buffer size.
In the file qavaudioframe.cpp there is a function named
QAVAudioFrame::data().It uses the resampler
swr_convert()(from swresample.h) in case the input stream's features (channel count, sample rate or format) does not match the desired output format (as returned byQAVAudioFrame::format()).If this is the case, the bool
needsConvertis true and then it is checked whether a (new) instance of the resampler need to be created, by callingswr_alloc_set_opts(). Usually this happens only once when a playback is started, and subsequent calls toswr_convert()does the actual resampling. It is important the instance stays alive for proper resampling.But because the resampler-state variables
d->swr_ctx,d->inSampleRateandd->outAudioFormatare members of the currentQAVAudioFrame, this essential resampler-state data is not available anymore on the next cycle, when the nextQAVAudioFramearrives. As a resultswr_alloc_set_opts()is called again and again, and proper resampling of the audio fails...Solution: I think that the variables
swr_ctx,inSampleRateandoutAudioFormatshould be part of QAVAudioOutputPrivate instead, where housekeeping is done per audio output. After all, each (imagine you have more than one) output device -- or any other samples-consumer -- have different needs.My quick and dirty fix:
QAVAudioFrame::data()is called fromQAVAudioOutputPrivate::readData().I created this struct:
This struct is a member of
QAVAudioOutputPrivateand I pass a reference to my slightly modifiedQAVAudioFrame::data()-->QAVAudioFrame::data(resampler_context_t & resampler_context).Now,
resampler_contextis used to store the resampler-state so it won't get lost. Nowswr_alloc_set_opts()is called once with the desired parameters and after that, on every next call, the same instance of the resampler is used and resampling works well.Like I said, my solution is really an ugly patch. Notice that I use a void-pointer as
QAVAudioOutputPrivatedoesn't need to know whatSwrContextlooks like. There must be a cleaner way that follows the design of QtAVPlayer.Finally, there is a strange line in the code where
outCountis calculated. This line should simply be:int outCount = frame->nb_samples;av_samples_get_buffer_sizetakes care of the math to calculate the buffer size.