ProbeTiming

A source that has been opened and read once, holding both the answer (info) and the open context that produced it.

A playback used to open its source twice: the host probes to decide how to play, then the remuxer opens again to produce. Over a network that second open is a real round trip and a real download — measured at a median of 54 ms even capped, on a link with no latency at all — and it happens inside the wait a user is watching.

The tempting shortcut is to keep the first open's conclusions and let the second context skip its analysis. That was tried in 1.1.2 and reverted: avformat_find_stream_info also fills fields the muxer needs (an EAC3 track's frame size, most sharply), so a context that never ran it produces a correct-looking manifest and a failing av_interleaved_write_frame. The analysis isn't redundant knowledge — it is state that lives in the context.

So the context itself moves. consumeContext() hands it over exactly once; whoever takes it owns closing it, and a ProbedSource that is never consumed (the host declined the source, or never started a session) closes its own on the way out.

Threading: an AVFormatContext is not safe for concurrent use, and this deliberately does not make it so. The handover is a move across threads — the probing side must be finished with it, which consuming it exactly once enforces structurally — not a share. The probe's cost, phase by phase. Each phase blocks on the transport, so on a network source these are transport numbers, not CPU numbers.