I created a timelapse video from iMovie software and set the time to 0.1 second for every image. But the final output is not satisfying. It seems a bit slow video. I need the clouds to move faster, but they are moving slowly. It is total of 30 second video. I need it to be 15 second video, so that I can get a desired effect. But I cannot change the setting lower then 0.1 second in iMovie. Any suggestions?
You can use ffmpeg, a command line program, to double the video speed:
ffmpeg -i input.mp4 -vf setpts=0.5*PTS output.mp4