http://muzso.hu/2015/04/25/how-to-speed-up-slow-down-an-audio-stream-with-ffmpeg
How to speed up / slow down an audio stream with ffmpeg
Sat, 2015.04.25 - 23:59 — müzso
https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20videoUse the "atempo" filter:
ffmpeg -i input.mp4 -filter:a "atempo=0.5" -vn output.aac
The above example will extract the audio stream from the input video, slow it down by 2 and reencode it into an AAC audio file.
The parameter for atempo must be between 0.5 and 2.0. If you want to slow it down even more, you can use the atempo filter more than once.
Eg. to slow it down by 4:
ffmpeg -i input.mp4 -filter:a "atempo=0.5,atempo=0.5" -vn output.aac
音頻用asetpts=PTS/2.0 是沒用的
