Only write OriginalPos to the index for video tracks
Don't write FrameType to the index file

It's never actually used after indexing is complete.
Fix seeking in open-gop h264 in lavf video
Persist has_b_frames for lavf and haali as well
Ensure that even very small buffers have enough padding
Fix crash when opening images
Make the interlaced H264 hack a bit more reliable
Fix corruption when seeking in interlaced H.264
Remove CPUFlags stuff from the avisynth plugin
Make the vapoursynth error handling less verbose
Remove unused things
Add BT.2020 values to FFMS_ColorSpaces
Extract some duplicated error handling stuff in the avs plugin
Use int64_t for file positions
Factor out some duplicated code in OutputFrame/OutputField
Use std::min/max rather than FFMIN/FFMAX
Use an initializer list to init AvisynthVideoSource
Fix unsigned underflow when seeking to the beginning of audio
Handle files where the first audio packet has multiple output frames

We need to decode the first packet to get the audio properties, but we
can't store the result since we don't know the output format yet.
Previously we just left the unconverted data in the output buffer to be
cached once we do know the output format, but that doesn't work when the
first package has multiple frames of audio, as only one can be saved.

Fix this by just flushing the cache and reopening the file whenever the
output format changes, which results in the first packet being decoded
twice, but that's not a huge deal. This also happens to add support for
changing the output format after getting audio.
Fix caching of audio with multiple frames per packet