what does the NGiNX RTMP DASH directive: dash_playlist_length do?

Question

I am looking for a way to send 5 second segments of video to from a camera to a user station. I have a working set up where I send mp4 file with ffmpeg to nginx (compiled with a rtmp-DASH module), and I retrieve it on a client user station with the MPEG-DASH reference java script. Which I can play over and over for about 2.5 minutes, then it goes away and has to be reloaded on the server.

I suspect the 'dash_playlist_length' directive has something to do with this but it does not seem to do anything. The documentation says:

Syntax: dash_playlist_length time 
Context: rtmp, server, application
Sets MPEG-DASH playlist length. Defaults to 30 seconds

but I come up empty handed trying to find what MPEG-DASH playlist length is. Search engines are not turning up anything useful. Does anybody here know what it does?

Answer 1

It defines how long the live/DVR window of the live stream should be, or in DASH terms it's called the timeShiftBufferDepth .

So if you set it to eg 60 seconds and stream for, say, 2 hours or however long, then still only the last (ie most recent) 60 seconds of the stream will be made available in the DASH manifest. So basically, it restricts how far the client is allowed to go back from the live edge of the stream while watching.