Various metadata-related features and improvements:

- Added support for new "NowMs" field that holds up to where no new packets are guaranteed to show up, in order to lower latency.
- Added support for JSON tracks over all TS-based protocols (input and output)
- Added support for AMF metadata conversion to JSON (RTMP/FLV input)
- Fixed MP4 input subtitle tracks
- Generalized websocket-based outputs to all support the same commands and run the same core logic
- Added new "JSONLine" protocol that allows for generic direct line-by-line ingest of subtitles and/or JSON metadata tracks over a TCP socket or console standard input.

src/input/input_buffer.cpp

@@ -349,6 +349,8 @@ namespace Mist{
       }
       for (std::set<size_t>::iterator idx = tracks.begin(); idx != tracks.end(); idx++){
         size_t i = *idx;
+        //Don't delete idle metadata tracks
+        if (M.getType(i) == "meta"){continue;}
         uint64_t lastUp = M.getLastUpdated(i);
         //Prevent issues when getLastUpdated > current time. This can happen if the second rolls over exactly during this loop.
         if (lastUp >= time){continue;}