GetAudioAccessorSamples stops before the end of video files

[cfillion]

GetAudioAccessorSamples stops writing to the given sample buffer before reaching the end of the file when reading video sources (tested using VLC and ffmpeg decoders with mp4(AAC-LC) and wma files). It returns 1 even if it did not write as many samples as requested.

SWS and scripts usually expect floor(itemLength * sampleRate) samples to be available in total. Because the current version of SWS does not initialize its sample buffer (fixing that), this leads to potentially grossly invalid Loudness measurements (as reported in issue #1210).



Here's a simple script (no windowing and mono only) that demonstrates the issue (test media files here):

item         = reaper.GetSelectedMediaItem(0, 0)
take         = reaper.GetActiveTake(item)
source       = reaper.GetMediaItemTake_Source(take)
channels     = reaper.GetMediaSourceNumChannels(source)
sampleRate   = reaper.GetMediaSourceSampleRate(source)
accessor     = reaper.CreateTakeAudioAccessor(take)
audioStart   = reaper.GetAudioAccessorStartTime(accessor)
audioEnd     = reaper.GetAudioAccessorEndTime(accessor)
audioLength  = audioEnd - audioStart
sampleCount  = math.floor(audioLength * sampleRate)
bufferSize   = sampleCount * channels
samples      = reaper.new_array(bufferSize)
garbage      = 0xcdcdcdcd
samples.clear(garbage)

retval = reaper.GetAudioAccessorSamples(accessor, sampleRate, channels, 0, sampleCount, samples)
reaper.DestroyAudioAccessor(accessor)

errors = {}

for i = 1, bufferSize do
  if samples[i] == garbage then
    table.insert(errors, i)
  end
end

if #errors == 0 then
  reaper.ShowConsoleMsg('Buffer is valid.\n')
else
  reaper.ShowConsoleMsg(string.format('GetAudioAccessorSamples stopped writing at sample %d (inclusive)! (%d invalid samples)\n', errors[1], #errors))
end

With "6khz sinewave.mp4" selected, it outputs:

GetAudioAccessorSamples stopped writing at sample 47105 (inclusive)! (1952 invalid samples)