When you tried to add the video initially, did it tell you that it needed to be processed? If it didn't, then we essentially detected that it was already encoded with the correct codecs, but despite this the browser doean't appear to be able to. You might find different browsers have different support, and you might find some browsers play it without issue.
In XFMG 2.0 we now have an option to transcode all videos regardless of detected support, which could be useful for cases like this.
If it did go through the processing (transcoding) stage and it came out like this, then that could be more problematic, though it could be an issue with the original file itself or with the FFmpeg version being used.
Ultimately though short of trying again, I can only suggest finding a different version of the video to upload, or attempting to convert it locally before uploading.