Fix bug when downsampling by a great factor (empty output frame) #586
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Mar 21, 2025
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This PR is based on #584 and includes changes from there.
This PR fixes the following bug:
which we hit on
https://github.com/pytorch/torchcodec/blob/4d894d55075eb1625a1443c54767bc92c31bc286/src/torchcodec/decoders/_core/VideoDecoder.cpp#L1484-L1487
In fact,
numConvertedSamplescan be 0 and this can be valid: if the input frames has very few samples, and if we're downsampling by a great factor, then swresample would buffer all the samples and just wait for the next samples to output anything. We thus allow an output converted frame to have zero samples. It's up to the caller to handle that case properly (our callers do natively handle this).