To trick Chrome into giving these videos the old college try, omit the "type" attribute. Chrome then tries to play the video, seems to realize it can, and we're back on track.
Since the "type" attribute is theoretically only useful to help browsers select among multiple different alternatives and we're only presenting one alternative, this seems likely safe and reasonable. Omitting "type" also validates. It's hard to be certain that this won't cause any collateral damage, but intuitively it seems like it should be safe and I wasn't able to identify any problems.