Seeking back to the beginning of the file in scanFileAndUpdateMetadataAndIndex

[NicolasHug]

In scanFileAndUpdateMetadataAndIndex, we first scan the entire file by receiving all packets in the container, calling av_read_frame() until the end of the video:

torchcodec/src/torchcodec/decoders/_core/VideoDecoder.cpp

Line 551 in d26bfbc

int ffmpegStatus = av_read_frame(formatContext_.get(), packet.get());

After this scan, we call av_seek_file to go back to the beginning of the file:

torchcodec/src/torchcodec/decoders/_core/VideoDecoder.cpp

Lines 593 to 594 in d26bfbc

	int ffmepgStatus =
	avformat_seek_file(formatContext_.get(), 0, INT64_MIN, 0, 0, 0);

(docs)

Specifically we pass:

• 0 as reference stream index
• 0 as the desired pts location

I wonder if we should instead pass:

• the best stream's index instead of 0. I feel like the best stream has a higher chance of being the correct reference to use when seeking.
• minPts as the desired pts location, instead of 0. As we've seen, some videos may start at negative pts values.