Redmine

Redmine does not perform any encoding or special handling of video files. Thus, to be able to play a video preview in your browser, it is required that your webbrowser supports the video and audio codecs used there. Some browser ship different codecs and thus may support different kinds of videos.

The H.263 video codes used by your video is not supported by any major webbrowser. To quote Mozilla's Code guide:

H.263 has never been widely used on the web. Variations on H.263 have been used as the basis for other proprietary formats, such as Flash video or the Sorenson codec. However, no major browser has ever included H.263 support by default. Certain media plugins have enabled support for H.263 media.
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H.263 is a proprietary format, with patents held by a number of organizations and companies, including Telenor, Fujitsu, Motorola, Samsung, Hitachi, Polycom, Qualcomm, and so on. To use H.263, you are legally obligated to obtain the appropriate licenses.

As such, I'm closing this issue as "Won't fix" as we do not plan to introduce video transcoding into Redmine as a core-feature. If this is required by you, you may be able to develop a plugin which transcodes video files to different formats if you have obtained the required licenses for the formats.