视频调速

a.md

Usage: speed-up-video <src> <dest> <factor> <framerate>

adjust-video-speed

#!/bin/bash

set -e

function print_help() {
    self_name="$(basename "$0")"
    echo "Usage: $self_name <src> <dest> <factor> <framerate>"
}

# if argument count is not 3, print help
if [ "$#" -ne 4 ]; then
    print_help
    exit 1
fi

# loop through arguments, if '-h' or '--help' presented, print help
for arg in "$@"; do
    if [ "$arg" == "-h" ] || [ "$arg" == "--help" ]; then
        print_help
        exit 0
    fi
done

src="$1"
dest="$2"
factor="$3"
framerate="$4"

factor="$(echo "scale=10; $factor" | bc 2>&1)"
if echo "$factor" | grep 'Runtime\ error' >/dev/null ||
    echo "$factor" | grep 'syntax error' >/dev/null; then
    echo "Invalid factor: $factor"
    exit 1
fi

# if factor <= 0, print error
if (($(echo "$factor < 0" | bc -l))); then
    echo "Error: factor must be a positive number"
    exit 1
fi

pts_multiplier="$(echo "scale=10; 1/$factor" | bc 2>&1)"
if echo "$pts_multiplier" | grep 'Runtime error' >/dev/null; then
    echo "Invalid factor: $factor"
    exit 1
fi

if (($(echo "$factor <= 2" | bc -l))); then
    filter_complex="[0:v]setpts=$pts_multiplier*PTS[ov]; [0:a]atempo=${factor}[oa]"
else
    log2="$(echo "scale=10; l($factor)/l(2)" | bc -l)"
    log_int_part="$(echo "scale=0; $log2 / 1" | bc)"
    remain_multiplier="$(echo "scale=10; $factor / 2^$log_int_part" | bc)"

    atempo_filter="[0:a]"
    for ((i = 0; i < log_int_part; ++i)); do
        if [ "$i" == 0 ]; then
            atempo_filter="${atempo_filter}atempo=2[oa$i]; "
        else
            atempo_filter="${atempo_filter}[oa$((i - 1))]atempo=2[oa$i]; "
        fi
    done

    atempo_filter="${atempo_filter}[oa$((i - 1))]atempo=${remain_multiplier}[oa]"
    filter_complex="[0:v]setpts=$pts_multiplier*PTS[ov]; $atempo_filter"
fi

echo "used filter: $filter_complex"

ffmpeg -i "$src" \
    -filter_complex "$filter_complex" \
    -map '[ov]' -map '[oa]' \
    -b:a 0 -b:v 0 -c:v h264_nvenc -r "$framerate" \
    "$dest"