Is it possible to speed up video with audio using ffmpeg, without changing audio pitch?

Question

Is there a relatively simple way to speed up a video (mp4, with aac encoded audio), by say "x1.25" or "x1.3" while keeping the original audio-video sync, but also retaining the original pitch of the audio ?

I've read some discussions about extracting audio track into separate file, then use rubberband to lower the pitch by the requisite value, and then merge the audio video tracks using ffmpeg with speed-up, which raises the pitch of the audio back again to original. However, it appears that this is a bit of hit-n-miss, because rubberband appears to use number of octaves as the parameter to raise or lower pitch, and this may not always align perfectly with the video, as musical notes / octaves have specific ratios. Also, this is cumbersome.

So, is there any simpler ways using ffmpeg alone ?

Answer 1

It can be done with ffmpgeg using a complex filter:

  ffmpeg -i input.mkv -filter_complex "[0:v]setpts=0.5*PTS[v];[0:a]atempo=2.0[a]" -map "[v]" -map "[a]" output.mkv

Documentation: https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video

The command above works if you want to multiply by 2 the speed. If you want to multiply by any <x>, the parameters become:

  ffmpeg -i input.mkv -filter_complex "[0:v]setpts=<1/x>*PTS[v];[0:a]atempo=<x>[a]" -map "[v]" -map "[a]" output.mkv

For instance, if you want to multiply by 1.15, the command is:

  ffmpeg -i input.mkv -filter_complex "[0:v]setpts=0.87*PTS[v];[0:a]atempo=1.15[a]" -map "[v]" -map "[a]" output.mkv

Answer 2

You can speed up video by 2.5X for example by doing this:

ffmpeg -i "input_video.mp4" -vf "setpts=(PTS-STARTPTS)/2.5" -af atempo=2.5 "input_video_2.5X.mp4"

Here is a bash script you can use for convenience (say convert_video.sh):

#!/bin/bash

# Arguments
FILE_RAW=$1
SPEED_FACTOR=${2:-1.0} # Default is 1.0 X speed

# Prepare variables
BASE_PATH=$(dirname $(readlink -f $FILE_RAW))
FILENAME_EXT="$(basename "${FILE_RAW}")"
FILENAME_ONLY="${FILENAME_EXT%.*}"
EXT_ONLY="${FILENAME_EXT#*.}"
FILENAME_ONLY_PATH="${BASE_PATH}/${FILENAME_ONLY}"

# Speed up/slow down video
ffmpeg -i "${FILENAME_ONLY_PATH}.${EXT_ONLY}" -vf "setpts=(PTS-STARTPTS)/${SPEED_FACTOR}" -af atempo=$SPEED_FACTOR "${FILENAME_ONLY_PATH}_${SPEED_FACTOR}X.${EXT_ONLY}"

Note: Make script executable: chmod +x convert_video.sh

Usage (Output File: <PATH_TO_INPUT_VIDEO>_<OPTIONAL_SPEED>X.mp4)

. <PATH_TO_THIS_SCRIPT>/convert_video.sh <PATH_TO_INPUT_VIDEO> <OPTIONAL_SPEED>

Example 1: Speed up video to 2.5X (Output: ~/Videos/input_video_2.5X.mp4)

. ~/convert_video.sh ~/Videos/input_video.mp4 2.5

Example 2: Slow down video to 0.5X (Output: ~/Videos/input_video_0.5X.mp4)

. ~/convert_video.sh ~/Videos/input_video.mp4 0.5

Hope it helps.

Answer 3

The code I used.

speed_change(){
    input=$1
    output=$2
    a_speed=$3
    v_speed=$(awk -v a_speed=$a_speed 'BEGIN{print 1/a_speed}')
    echo -e "\nSpeed up ${a_speed}X, para to atempo is ${a_speed}, para to setpts is ${v_speed}.\n"
    ffmpeg -i $input -c:v hevc_videotoolbox -vf "setpts=$v_speed*PTS" -af atempo=$a_speed $output
}