FFmpeg compress to filesize

ffconv.sh

#!/bin/bash

if [ "$#" -lt 2 ]; then
    echo "Usage: $0 <input_file> <output_file> [target_size_MB]"
    exit 1
fi

input="$1"
output="$2"
target_size=${3:-20}  # Default to 20MB if not specified

# Get the duration of the video in seconds
duration=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "$input")

# Calculate the bitrate to achieve the target size
bitrate=$(echo "$target_size*1024*1024*8/$duration" | bc)

# Determine the format from the output file extension and set codecs accordingly
case "${output##*.}" in
    webm)
        video_codec="libvpx-vp9"  # Using VP9 for WebM
        audio_codec="libvorbis"
        hwaccel="-c:v h264_cuvid"
        ;;
    mp4)
        video_codec="h264_nvenc"
        audio_codec="aac"
        hwaccel="-c:v h264_cuvid"
        ;;
    *)
        echo "Unsupported format. Only webm and mp4 are supported."
        exit 1
        ;;
esac

# Convert the video using the calculated bitrate and the determined codecs
ffmpeg $hwaccel -i "$input" -c:v $video_codec -b:v ${bitrate} -c:a $audio_codec "$output"

It uses hardware acceleration so you need CUDA!

Usage:
ffmpeg input.mp4 output.mp4 49 to keep it under 50mb

you can also do it mp4 to webm, but it's slow (probably a bug/bad config) I recommend converting to mp4 first then using that to make it a webm.