git rebase -i --committer-date-is-author-date HEAD~n
git push --force

• rebase modifies history in a few ways, such as rewording commits
• -i (short for --interactive) lets you chose specific commits to reword
• --committer-date-is-author-date (optional) keeps original date instead of updating it
• HEAD~n reference, current branch n commits back

Force pushing is needed since history is modified, will cause trouble if you work with other people.

ffmpeg -i input.mkv -vf "setpts=PTS/60" -r 60 -an output.mp4

(Some of the following options link to further information.)

• -i input.mkv input file
• -vf (short for --filter:v) video filter, "setpts=PTS/60" set presentation timespamp
• -r 60 frame rate
• -an no audio (unless you speed up audio too, the output's length will stay the same)
• output.mp4 output file and format