Chromium doesn't play mp4 / h.264 files in video tag

Firefox plays movie on the page:

Chromium doesn't. it just shows the static backround image.

when i dig the page source and access the file directly:

chromium plays it without any problem.

when i download the file, any video player plays the file without any problem

smplayer says:

Resolution: 460 x 258
Aspect ratio: 1.78295
Format: h264
Bitrate: 0 kbps
Frames per second: 30.000000
Selected codec: H.264

i have ubuntu mate 14.04 64bit, chromium 65.0.3325.181 (same observed on kubuntu 18.04 64bit, chromium 71.0.3578.98). i have installed chromium-codecs-ffmpeg-extra and x264

how to make chromium plays it?

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