yt-dlp messages are matched against a regex table kept as data, so the
classification is unit-testable without the network and can be amended when
YouTube changes its wording. Only network failures and aria2 process failures
retry; a private video will still be private on the third attempt, and disk
exhaustion is fatal rather than per-job.
The retry loop is ours because it has to be: ExternalFD.real_download calls the
downloader exactly once and turns a nonzero exit into report_error(), so
yt-dlp's own `retries` never covers aria2c. Since --lowest-speed-limit
deliberately makes aria2c exit nonzero on a stall, without this loop that stall
would end the job instead of resuming it -- the .aria2 control file survives, so
each attempt picks up where the last stopped.
A missing aria2c downgrades to the native downloader with a warning rather than
failing the run.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
JMR-devandClaude Opus 5
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