Most likely, you use some unsupported video format; or the video container file contains media using one or more of unsupported codecs. Please see:
http://en.wikipedia.org/wiki/HTML5_video#Supported_video_formats[
^],
http://en.wikipedia.org/wiki/HTML5_video#Patented_formats[
^],
http://en.wikipedia.org/wiki/HTML5_video#Free_formats[
^],
http://en.wikipedia.org/wiki/Use_of_Ogg_formats_in_HTML5[
^].
Practically, you should provide only Ogg Theora or WebM formats with the use of compatible codecs. Please see:
http://en.wikipedia.org/wiki/Theora[
^],
http://en.wikipedia.org/wiki/WebM[
^].
How can you do this if your available format is different? You can use different software project to
remaster the video you already have, but I would strongly recommend FFmpeg or libavcodec utility. Please see:
http://en.wikipedia.org/wiki/Ffmpeg[
^],
http://ffmpeg.org/[
^],
http://en.wikipedia.org/wiki/Libavcodec[
^],
http://libav.org/[
^].
In both cases, you can get free open-source utilities which can make nearly everything.
The selection of good sets of encoding parameters to provide a reasonable trade-off between size of the file and quality is a separate song. You may need to experiment for a while and read some practical recommendation to gain enough experience.
Good luck,
—SA
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