One CPython interpreter caps sustained segment throughput at ~160 MB/s;
spawned children each run the existing thread-pool path on a contiguous
chunk of the batch, reaching NIC line rate on fast CDNs. Opt-in via
--download-processes (default 1), engaged only for 24+ segment batches.
Sessions are rebuilt per child from a picklable spec; RnetSession falls
back to a single process when it has no impersonate preset.
Share one best-audio selector across the episode and music paths so best/all works for songs, descriptive audio is capped to one track, and codec_priority is honored. Guard --channels and 16:9 canvas math against tracks missing channel/width metadata. Extend --best-available to video languages and full resolution misses in both normal and hybrid mode, and count only deliverable ranges when reporting missing resolutions. Rank video by resolution before bitrate, and trim group audio selections to one track per song with a warning.
BREAKING CHANGE: a missing resolution with -r HYBRID now errors without --best-available, matching non-hybrid behavior.
imSp4rky