How to slow a video
1. Drop a short video you already have. A photo or an audio file is refused here. 2. Leave half speed, or pick quarter speed. 3. Press “Slow motion” and download the MP4.
GustKit runs the FFmpeg setpts filter. Half speed uses setpts=2*PTS, so a 1 second clip lasts about 2 seconds. Quarter speed uses setpts=4*PTS. When the file has a soundtrack, atempo slows it by the same amount so the voice stays lined up. A silent clip still slows: the picture is written without audio.
Only slower, not a speed dial
Change video speed can also speed a clip up, and it accepts a custom number from 0.25 to 4. This page only stretches to twice or four times the length. It does not trim the start or the end. Keep the original until the download looks right.
The clip stays in this tab
FFmpeg runs in this browser. GustKit does not fetch video from a link. Close the tab and the file is gone. Clips up to the limit shown next to the button, because the result is longer than the file you dropped.
How to check the slow motion
1. Play the download next to the original. 2. A moment that was halfway should arrive later. Half speed should last about twice as long. 3. If the download is not MP4, you opened a different page.
Change video speed can also speed a clip up. This page runs the FFmpeg setpts filter and only stretches to twice or four times the length. Nothing is uploaded.