udp streaming and webm

[Trevor Clarke]

I'm trying to generate a UDP stream encoded with webm/vp8 and I'm having
some issues. My source pipeline is:

videotestsrc is-live=true ! videoconvert ! vp8enc ! webmmux streamable=true
! chopmydata max-size=9000 ! udpsink qos=true sync=true host=127.0.0.1
port=5432 bind-address=127.0.0.1

Eventually this will be multicast udp but I'm using loopback for testing.
The chopmydata is there to ensure the data packets are below the MTU (all
machines and network equip can handle big packets).

I'm testing the stream in VLC and connect to udp://@:5432

If I start VLC then start gst-launch-1.0 everything works fine. However, if
I start gst-launch first, then VLC (or stop gst-launch then start it again
without restarting VLC) I see no video. VLC reports that packets are being
received but no video is decoded.

If I use gst-discoverer-1.0 on udp://127.0.0.1:5432 and start that before
the stream it detects webm/vp8. If I start the stream first I get an error
"Could not determine type of stream."

My guess is that I haven't configured the codec or the container to include
additional headers or something similar. Is this even possible with
webm/vp8? I've successfully set this up with x264enc ! mpegtsmux  which are
typically used for this sort of thing but one of my clients will be a web
browser (via a udp to websocket proxy and MediaSource extensions) so mpegts
is not an option.
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