ffmpeg video compression / specific file size

Question

Currently I have 80mb movies that I want to use ffmpeg to convert down to say about 10mb or 15mb. I know there will be a quality loss but they will need to have sound. Is there a way to either specify a file size or higher compression than what I have done previously

ffmpeg -i movie.mp4 -b 2255k -s 1280x720 movie.hd.ogv 

They are currently about 25mb a piece

Answer 1

if you are targeting a certain output file size the best way is to use H.264 and Two-Pass encoding.

There is a great example here but it's too large to copy-paste: https://trac.ffmpeg.org/wiki/Encode/H.264#twopass

You calculate your target bitrate using bitrate = target size / duration and you launch ffmpeg two times: one pass analyzes the media and the second does the actual encoding:

ffmpeg -y -i input -c:v libx264 -preset medium -b:v 555k -pass 1 -c:a libfdk_aac -b:a 128k -f mp4 /dev/null && \ ffmpeg -i input -c:v libx264 -preset medium -b:v 555k -pass 2 -c:a libfdk_aac -b:a 128k output.mp4 

Edit: H.265 (HEVC) is even better at compression (50% of H.264 size in some cases) but support is not yet widespread so stick with H.264 for now.

Answer 2

Inspired by Hashbrown's answer. This version keeps the original audio quality, and resizes to the target size.

NEW

1. Renamed variables for readability and consistency.
2. Removed dependency on grep (-P switch not implemented in OSX grep)
3. The script now exits with a helpful message if target size would be too small.

Script

#!/bin/bash # # Re-encode a video to a target size in MB. # Example: #    ./this_script.sh video.mp4 15  T_SIZE="$2" # target size in MB T_FILE="${1%.*}-$2MB.mp4" # filename out  # Original duration in seconds O_DUR=$(\     ffprobe \     -v error \     -show_entries format=duration \     -of csv=p=0 "$1")  # Original audio rate O_ARATE=$(\     ffprobe \     -v error \     -select_streams a:0 \     -show_entries stream=bit_rate \     -of csv=p=0 "$1")  # Original audio rate in KiB/s O_ARATE=$(\     awk \     -v arate="$O_ARATE" \     'BEGIN { printf "%.0f", (arate / 1024) }')  # Target size is required to be less than the size of the original audio stream T_MINSIZE=$(\     awk \     -v arate="$O_ARATE" \     -v duration="$O_DUR" \     'BEGIN { printf "%.2f", ( (arate * duration) / 8192 ) }')  # Equals 1 if target size is ok, 0 otherwise IS_MINSIZE=$(\     awk \     -v size="$T_SIZE" \     -v minsize="$T_MINSIZE" \     'BEGIN { print (minsize < size) }')  # Give useful information if size is too small if [[ $IS_MINSIZE -eq 0 ]]; then     printf "%s\n" "Target size ${T_SIZE}MB is too small!" >&2     printf "%s %s\n" "Try values larger than" "${T_MINSIZE}MB" >&2     exit 1 fi  # Set target audio bitrate T_ARATE=$O_ARATE   # Calculate target video rate - MB -> KiB/s T_VRATE=$(\     awk \     -v size="$T_SIZE" \     -v duration="$O_DUR" \     -v audio_rate="$O_ARATE" \     'BEGIN { print  ( ( size * 8192.0 ) / ( 1.048576 * duration ) - audio_rate) }')  # Perform the conversion ffmpeg \     -y \     -i "$1" \     -c:v libx264 \     -b:v "$T_VRATE"k \     -pass 1 \     -an \     -f mp4 \     /dev/null \ && \ ffmpeg \     -i "$1" \     -c:v libx264 \     -b:v "$T_VRATE"k \     -pass 2 \     -c:a aac \     -b:a "$T_ARATE"k \     $T_FILE 

NOTES

• See comments for a possible Windows version.

SOURCES

Hashbrown's answer (in this thread)

Two Pass method