libmp3lame is single-threaded, so concurrency is one ffmpeg process per file
and the pool width is the whole of it. The width came from os.cpu_count(),
which reports the host's cores and ignores a container's cpus: allowance -- on
a 12-thread host limited to 4 CPUs that is threefold oversubscription, which
costs context switches and NAS responsiveness for no throughput.
The default now reads the cgroup v2 quota, falling back to process CPU
affinity and then to the host count. Each pass logs the number it chose.
Also stops probing every file for embedded cover art. The probe only changes
the command when a cover file sits beside the track, so ask only then; with no
cover file, -map 0:v:0? already carries embedded art if there is any. Worth
roughly 30 ms per track against about 4 s of encoding, so this is tidiness
rather than a speed-up. The per-directory cover lookup is cached alongside.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
