threads=auto spawns one decode thread per logical core per decoder (16
observed on a 24-core box); with cores-2 render workers decoding
concurrently the machine is oversubscribed several times over and the
playback-audio render thread gets starved (late chunks are dropped).
4 threads decode 1080p h264 far past real-time; preview throughput comes
from the worker pool, not per-decoder threading. Applies to both the
software open path and the hwaccel open path.
Mike-Solar
81c3839937