Reverse Video

Make a video play backwards: water flowing up, a jump in reverse, a cake un-baking, or a rewind effect for a social clip. Reverse the whole video or just a part of it, with the sound reversed as well, removed, or still playing forwards. The reversed clip is an H.264 MP4 made in your browser with the ffmpeg engine (about 30 MB, downloaded the first time); your video is never uploaded.

How to use this tool

1. Optionally enter the part to reverse (from and until); leave both empty for the whole video.
2. Choose what happens to the sound and the maximum resolution.
3. Choose the video; reversing starts right away and shows its progress piece by piece.
4. Play the result and download it.

Formula

Output frame k = input frame (N − 1 − k), for the N frames of the chosen part

Reversing has to hold frames in memory, because the last frame is needed first. To stay within the browser's memory, the part is cut into short pieces (a few seconds at 1080p, longer at lower resolutions), each piece is reversed, and the pieces are joined in reverse order without another re-encode. The sound is reversed piece by piece in the same way, so it stays in step with the picture. AVI files are first copied into an exact high-quality intermediate, because AVI cannot be cut reliably at an arbitrary time.

Example

A 12-second 1080p clip at 30 fps is 360 frames. At the default 720p maximum it is reversed in about one minute on a recent computer (in 4 pieces); kept at 1080p it takes about a minute and a half (8 pieces). Either way the result is again 12 seconds long, frame for frame in reverse order.