How can speed up a video by 2X in ffmpeg?

# 1.25x speed
ffmpeg -i origin.mp4 -filter_complex "[0:v]setpts=0.8*PTS[v];[0:a]atempo=1.25[a]" -map "[v]" -map "[a]" fast.mp4

# 2x speed
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

# 2x speed
# chatgpt generate the cli
ffmpeg -i input.mp4 -filter:v "setpts=0.5*PTS" -filter:a "atempo=2.0" output.mp4

ffmpeg -i input.mp4 -filter:v "setpts=PTS/2" fast.mp4 only speed up video

shell script

Thank ChatGPT

#!/bin/bash

# Ask the user for the input video file
read -p "Enter the path to the input video file: " input_file

# Ask the user for the speed multiplier
read -p "Enter the speed multiplier (e.g. 2 for 2x speed): " speed_multiplier

# Build the ffmpeg command with the input file and speed multiplier
ffmpeg_command="ffmpeg -i $input_file -filter:v \"setpts=$(bc -l <<< "1/$speed_multiplier")*PTS\" -filter:a \"atempo=$speed_multiplier\" output.mp4"

# Run the ffmpeg command
eval $ffmpeg_command

echo "Done!"

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