Allow partial AVFRingBuffer reads

[danielk]

Traditionally we've always had RingBuffer::Read() return the number of bytes requested unless we are at the end of the file. But this blocks libav which expects this the read to complete fairly quickly even if it is a blocking read. Instead we should block for only a short time waiting for more data and then return what data we do have as long as we have at least 1 byte of data.

[danielk]

Initial patch

[danielk]

With some debugging I've discovered that if you return -EAGAIN a number of times to libav it will mark the stream as having hit EOF. Even if you later reset the EOF flag any partially decoded data will be chucked by libav.

This means this solution is unworkable as is. However, we can still return partial reads as long as we avoid returning zero byte reads or -EAGAIN reads.

[danielk]

Rework which allows short reads, but still avoids ever returning 0 bytes.

[anonymous]

debugging patch

[JYA]

most of this is now unecessary as 1- ffmpeg doesn't consider having reached EOF when Read returns 0 2- RingBuffer::run will manage small read