Speeding up a clip and reducing frame rate

Help/How To
1

I have a 6 hour video clip of the night sky recorded at 20FPS. I am using this to create a star trail picture and hopefully a timelapse of the star trail

I plan to export images from the video using Shotcut (1 image for every frame), then process them using Startrax, and use the resultant Startrax images to import into Shortcut to create the timelapse

To avoid processing 6 hours of video and tens of thousands of images, I was considering speeding up the video first using Shotcut, but I am not sure how Shotcut implements the speed up. Does it simply increase the playback frame rate, does it drops frames, does it do something else

Ideas & thoughts on a postcard

2

The export process will grab the frame closest to the “requested” time. So if you do 2x on a video then export, then it will basically skip every other frame, at 10x it will output 1 frame out of every 10 etc. The export and video mode fps are important but I assume it’s just 20fps on both.

But as a suggestion, if you just want to make jpegs out of an mp4 file use ffmpeg directly and it shoul be waaay faster. From this stackoverflow answer you can simply write this command in cmd:

ffmpeg.exe -i "filename.mp4" "frames/out-%06d.jpg"

You can use chatgpt or other ai to tweak this but it should be straightforward.

  • ffmpeg.exe is in the Shotcut’s directory if you don’t want to download it separately.
  • the 6 in %06d part of the output jpg sequence basically allows for 6 digits so from out-000001.jpg to out-999999.jpg - should be enough for 6hours
3

It will execute faster, but you will have spent more time figuring out how to get what you want (skip N/M frames and use command line). Meanwhile, in Shotcut:

  1. Settings > Video Mode > Automatic
  2. Open video in Source viewer
  3. Properties > Speed (yes, it drops frames)
  4. Export > Preset > stills > (choose one)
  5. Export File
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