magic ffmpeg calls

ffmpeg calls

# pack a bunch of images into a nice-looking gif running at 5 fps (with rescaling and a proper color palette)
ffmpeg -f image2 -r 5 -i %*.png -vf "scale=450:-1,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" out.gif

# convert section of video to gif (with palette, rescale and slowdown)
 ffmpeg -ss 00:00:43 -to 00:00:49.5 -i input.mp4 -r 15 -vf "scale=300:-1,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse,setpts=2.0*PTS"  out.gif


# shrink a video (half the size and _slightly_ lower quality)
ffmpeg -i input.mp4 -vf scale="iw/2:ih/2" -crf 30 output.mp4

multi_ffmpeg.sh

#!/usr/bin/env bash

# Re-compress a whole folder of videos to some maximum size
#
# Usage:
#   ./multi_ffmpeg.sh /path/to/folder/of/videos
#
# Output is written to new folder   /path/to/folder/of/videos_encoded
#

set -e

MAX_PIXELS=1440  # max pixels on the longest side of the video. larger videos will be shrunk, smaller ones stay small.
CRF=22  # bigger number = more compression. https://trac.ffmpeg.org/wiki/Encode/H.264#a1.ChooseaCRFvalue

INPUT_DIR="$1"
[ -z "$INPUT_DIR" ] && { echo "Usage: $0 /path/to/folder"; exit 1; }

OUTPUT_DIR="${INPUT_DIR}_encoded"
mkdir -p "$OUTPUT_DIR"

for file in "$INPUT_DIR"/*; do
  [ -f "$file" ] || continue

  base="$(basename "$file")"
  base_no_ext="${base%.*}"
  out="$OUTPUT_DIR/${base_no_ext}.mp4"

  echo "Processing $file -> $out"

  # re-encode with
  # - scale of the largest side <= MAX_PIXELS
  # - pixel format yuv420p because not every player understands yuv444
  # - something something for audio
  ffmpeg -i "$file" \
    -vf "scale='if(gte(iw,ih),min(iw,$MAX_PIXELS),-2)':'if(gte(ih,iw),min(ih,$MAX_PIXELS),-2)'" \
    -c:v libx264 \
    -pix_fmt yuv420p \
    -crf $CRF \
    -c:a aac -b:a 128k \
    -y "$out"
done

echo "All done! Encoded files are in: $OUTPUT_DIR"