Slow down a Matroska-contained movie to correct for PAL speedup.
In regions that historically used the PAL television standard, films shot at 24 frames per second (fps) were converted for television (including VHS and DVD) at 25 fps, resulting in a 4% speedup with audio pitched up by nearly a semitone. This problem generally does not affect newer digital formats (e.g. Blu-ray), except in rare cases where a "new" release is created by upscaling an older transfer that already exhibits speedup. (Looking at you, Doctor Who TV movie!) Learn more about PAL speedup here.
This script forces a framerate change to the video track(s), avoiding re-encoding and leaving the underlying data alone. Audio tracks are slowed to match and re-sampled at their original sample rates, fixing the pitch issue and ensuring audio and video remain in sync. Subtitles and chapters are re-timed to match.
I prefer this solution to re-encoding the entire video, as the latter adds the possibility of quality loss. The resulting framerate will almost always be nonstandard, but capable video players (e.g. VLC) have no issue with this -- and there is no excuse in this day and age for video players not to support arbitrary framerates. (Resampling audio is unfortunately unavoidable, since many audio formats only support a small set of sample rates.)
Portions of this script were adapted from code posted by James Ainslie here. These portions are marked.