There are numerous ways to encode mp4 videos, and encoding them for mobile devices is even more complex. I'm not sure what you mean by "low cost mobile" do you mean low cost as in the device, or the bandwidth needed to play said video? Either way, here a post to get you going: H.264 WEB VIDEO ENCODING TUTORIAL WITH FFMPEG Examples Here are some ffmpeg examples from the post ... “Standard” web vide
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