Does the default browser on Lumia 800 support HTML5's video element? According to various MS pages it should (for example ) but I can't get it to work in anyway.

I've transcoded a video using ffmpeg to mp4 and webm and I can successfully play this video on iPhone and Android phones but no luck on Lumia so far. ffprobe reports the following about my mp4 file,
Duration: 00:02:19.64, start: 0.000000, bitrate: 314 kb/s
Stream #0.0(und): Video: h264, yuv420p, 480x320, 246 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc
Stream #0.1(und): Audio: aac, 48000 Hz, stereo, s16, 63 kb/s

Should this work on Lumia? Can anyone provide any information on how to transcode a video with ffmpeg to a format that works on Lumia?