Virtual Channels for Stitcher

[matvp91]

The idea is to construct a schedule, a list of ScheduleItem.

[
  {
    start: 1727727770280,
    end: 1727727830280,
    uri: "mix://66ddcdd1-2d36-48b5-89cd-edf13bf813d6"
  },
  {
    start: 1727727830280,
    end: 1727728170280,
    uri: "mix://b0acc946-0f38-4399-babc-aebee8f517a5"
  }
]

Stitcher can then consume the schedule and expose segments gradually over a clock. This would simulate a live channel with pre-configured assets defined in the schedule. Also introduce EXT-X-MIX-SLIDING-SIZE=60.000 to indicate the dvr range. Either that or we can intercept the playlist on the client and calculate it ourselves.