lavf: Add an MPEG-DASH ISOFF segmenting muxer

This is mostly to serve as a reference example on how to segment
the output from the mp4 muxer, capable of writing the segment
list in four different ways:
- SegmentTemplate with SegmentTimeline
- SegmentTemplate with implicit segments
- SegmentList with individual files
- SegmentList with one single file per track, and byte ranges

The muxer is able to serve live content (with optional windowing)
or create a static segmented MPD.

In advanced cases, users will probably want to do the segmenting
in their own application code.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/allformats.c

@@ -88,6 +88,7 @@ void av_register_all(void)
     REGISTER_DEMUXER (CDG,              cdg);
     REGISTER_DEMUXER (CDXL,             cdxl);
     REGISTER_MUXER   (CRC,              crc);
+    REGISTER_MUXER   (DASH,             dash);
     REGISTER_MUXDEMUX(DAUD,             daud);
     REGISTER_DEMUXER (DFA,              dfa);
     REGISTER_MUXDEMUX(DIRAC,            dirac);