Despite all the hype, in reality the HTML5 video tag has a bit of a problem. In order to use it and for it to be cross browser compatible, you have to include more than one format of the video. To target all supported browsers these formats are mp4 and ogg.
I was searching around for optimum settings for each format but unfortunately I couldn't find any. I'm using ffmpeg 0.6 which has the tagline "Works with HTML5". I'm no video expert so I was wondering if anyone could recommend decent settings for each format?
I ended up using ffmpeg and ffmpeg2theora.
WebKit compatible h.264 video
I decided to go for the ipod640 preset because it means the video can be viewed nicely on an iPhone or iPod touch. Of course, you can change the settings around a bit, get rid of the '-vpre ipod640', change the resolution or quality. Anyway the command is:
ffmpeg -i video_source_file.ext -vcodec libx264 -vpre ipod640 -b 250k -bt 50k -acodec libfaac -ab 56k -ac 2 -s 480x320 video_out_file.mp4
move some information to the front of the file so the video can play before it loads
qt-faststart video_out_file.mp4 video_out_file_quickstart.mp4
Firefox compatible Ogg video
This depends on you having ffmpeg2theora installed. Also, I have only tested it with the input file being the output file from the previous ffmpeg conversion. The command is:
ffmpeg2theora -o video_out_file.ogv video_out_file.mp4
来源：https://stackoverflow.com/questions/3119797/ffmpeg-settings-for-converting-to-mp4-and-ogg-for-html5-video