cast_dl_params feeds ctx.params to dl() and dl.result() as on the CLI. A string lang value now returns 400 instead of splitting into letters, and -r accepts HDR10+.
A tag with a region (en-US, es-419) matches only that variant and reports a miss instead of taking another region. A bare tag takes the variant it means (pt -> pt-BR, es -> es-ES) and falls back to any variant only when that one is missing. `orig` prefers the title's own tag, `-sl orig` resolves, forced and SDH subtitles are picked from their own pools, and the track name no longer strips the region from the cached language.
BREAKING CHANGE: -l es-419 no longer selects es-ES, and language_priority, language_tags and muxing.default_language treat a regional tag as exact.
Each keeps one kind of track inside its track type. A run of more than one title skips a title that has no such track. The REST API rejects a non-boolean value for a boolean dl param, and the DASH parser reads audio description from Role elements.
Gate a title on audio or video languages that must exist, independent of what -l/-al/-vl select. --require-subs joins the same gate: its --s-lang conflict and download-all side effect are gone, so -sl now decides what to keep. Requiring a language that is also excluded fails at parse time.
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