The day long video was made on and posted from my Mac, on which Firefox happily plays back the videos, but my Mac is old and ffmpeg only manages to encode the videos at about 2fps. I'm not curious enough to boot Windows and find out. Lack of H264 decoding capability I guess, which I would guess means they won't work on Firefox on Windows either. I can play the videos on my Linux machine, (I made them on my Linux machine), just not in Firefox. I've just realised these videos don't play in Firefox on my Linux machine. The -movflafs faststart argument tells ffmpeg to 'Run a second pass moving the index (moov atom) to the beginning of the file.' This means that when the video is viewed in a web browser playback can start straight away rather than waiting for the entire video to be downloaded. Then use ffmpeg's concat demuxer $ ffmpeg -f concat -i list.txt -c copy -movflags faststart webcam2013.mp4 To join them up you need to make a list of all the filenames $ for i in mp4s/* do echo "file '$'" done > list.txt On a 1.6Ghz Intel Core Duo a single video took about five and half minutes and on an ARM Marvell Kirkwood 1.2GHz it took about 42 minutes.) It took about two hours to generate all the videos on a 2.8Ghz Intel Core 2 Quad. $ ffmpeg -r 48 -pattern_type glob -i '*.jpg' -an -vcodec libx264 -f mp4 -threads 0 -b:v 1000k foo.mp4 The command for each day's video looks like It also reduces the risk of leaving something running, checking it two hours later and finding all the output is garbage. For example I noticed the video for 20th March had a considerably smaller filesize than the others and that the videos for 19th and 21st were also slightly smaller than average. It could be done all in one go but making separate videos means it's easier to spot issues. I put the video together by making a video for each day then joining them up.
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