Tech Recipies/Improving MJPEG movies taken by digital cameras \\ Many consumer-grade digital cameras (like the Canon A95) can record movies in the {link:Motion JPEG format|http://en.wikipedia.org/wiki/MJPEG}, in which each frame is represented as an independent JPEG image. Most digital cameras can manipulate this format with ease because of their JPEG-processing prowess. The MJPEG format, however, does have some notable drawbacks: - __Low compression.__ Because each frame is independent, inter-frame similarities cannot be "factored out" and compressed away. - __Exaggerated noise.__ JPEG compression results in small noise-like artifacts that are hard to notice in a single frame but jump out in movies, where inter-frame differences are easy to see. 1.1 Re-encoding MJPEG movies to improve compression and perceived quality To get around these problems, I re-encode my digicam's MJPEG movies using the following ~~mencoder~~ recipe: {code:none} mencoder ~~input.avi~~ __-vf eq2=1.6,hqdn3d__ -oac copy -ovc lavc -o ~~output.avi~~ {code} The magic occurs in the video-filter specification (in bold), which comprises two post-decoding processing steps: - __eq2=1.6__ – Increases the gamma setting to 1.6, brightening the movie. (I find that movies captured indoors are often too dark.) - __hqdn3d__ – Filters the video using a high-quality version of the ~~denoise3d~~ filter, which "aims to reduce image noise, producing smooth images and making still images really still." To preview the effects of these filters before re-encoding with them, you can try them with ~~mplayer~~: {code:none} mplayer ~~input.avi~~ -vf eq2=1.6,hqdn3d {code} 1.1 QuickTime compatibility The ~~ffmpeg~~ tool can be used to re-encode movies for QuickTime compatibility: {code:none} ffmpeg -i ~~input.avi~~ ~~output.mp4~~ {code} To avoid re-encoding artifacts, use a lossless codec in the initial ~~mencoder~~ step: {code:none} mencoder ~~input.avi~~ -vf eq2=1.6,hqdn3d -oac copy __-ovc lavc -lavcopts vcodec=ffvhuff:vstrict=-1__ -o ~~temp.avi~~ ffmpeg -i ~~temp.avi~~ ~~output.mp4~~ rm -f ~~temp.avi~~ # the temp file can be large {code} 2005-12-21 18:10:00.574 2005-12-21 17:10:04.004