Add demux_read_interrupted(), true when the demuxer is being canceled,
its thread is terminating, or a seek is queued. Poll it from
demux_lavf's AVIO interrupt callback so blocking network I/O (e.g. the
HLS demuxer waiting on a live playlist reload) doesn't stall queued
seeks or shutdown for multiple seconds. The aborted read's result is
discarded in all of these cases anyway.
In normal operation demuxer reads are fast enough to not notice the
issue. However, in the HLS/DASH demuxers, FFmpeg blocks read() calls
on the playlist reload timeout. This is expected, but can mean multiple
seconds of dummy wait before we can actually proceed. This change
significantly speeds up seeking in HLS playback when it hits a playlist
reload.
Kacper Michajłow
48e6c35c0e