Merging split audio and video streams on desktop

"av" here is audio/video.

Adaptive sources hand out audio and video as separate URLs. On Android the player library has a merging media source for exactly this; a C media engine embedded in a JVM desktop app usually has an equivalent, in the form of an inline edit-list URL naming several streams that play simultaneously.

The important property: the result is still one source, so it is one handle. Transport, position reporting and release are unchanged — there is no second handle to keep in sync.

The URL shape

Each entry is preceded by a header saying "this is a new simultaneous stream" rather than the next item in a sequence, and every URL is length-quoted: