shrink

Make an image, video or PDF fit a size.

Synopsis

shrink [options] file size
shrink -s size [options] file ...

Description

A form takes uploads up to 2 MB. A chat app takes videos up to 25 MB. shrink writes a smaller copy of the file that fits the size you give, and keeps as much quality as it can on the way.

photo.jpg -> photo-small.jpg (4.8MB -> 1.9MB, quality 85, 0.9s)

The copy goes beside the file as name-small.ext, or name-small-1.ext when that name is taken. The original is never changed. When the file already fits, shrink says so and writes nothing.

Sizes read like 500K, 25M or 1.5G, in steps of 1024. The target must be 1K or more.

Each kind of file has its own way down:

shrink knows the kind from the ending. For a file without a known ending, it asks file what it holds.

Options

Images

shrink strips the metadata from every image and turns it the right way up first. The metadata holds the camera, the date and often the GPS position, and it can weigh 50 KB or more.

For JPEG, WebP, AVIF, HEIC and JPEG XL it then tries the qualities 85, 75, 65, 55 and 45 at full width, and keeps the highest one that fits. When even 45 is too big, it tries 85%, 70%, 55%, 40%, 30%, 20% and 10% of the width, with the same quality search at each one. PNG, GIF, TIFF and BMP have no quality setting, so only the width changes.

The result line says what it took, such as quality 65, 55% wide. The ending of the -o name picks the format, so -o photo.webp converts a JPEG to WebP on the way. -w 1920 caps the width before the search starts, which suits photos from a phone that are 4000 pixels wide.

Video

shrink reads the length of the clip and works out the bitrate that fills the target. It keeps 3% back for the container and 96 kbit/s for the sound. Then ffmpeg encodes the clip twice. The first pass measures the clip and the second one spends the bits where the picture needs them. That makes the size land close to the target.

When the copy still comes out too big, shrink tries once more at a lower bitrate. When that fails too, it writes nothing.

A clip with no sound stays silent. -w 1280 scales the video down as well, which looks better than a low bitrate at full size. Below 50 kbit/s for the picture the result is not worth watching, so shrink stops and says the target is too small for the length.

PDF

Ghostscript rewrites the PDF with one of its presets. shrink tries them in order and stops at the first that fits.

A PDF of plain text is mostly fonts, and no preset makes it much smaller. A scanned PDF is mostly images, and shrinks a lot.

Pass-through

Options after -- go to magick for images, to both ffmpeg passes for video and to gs for PDF:

$ shrink talk.mp4 25M -- -preset slow
$ shrink photo.jpg 500K -- -sampling-factor 4:2:0
$ shrink scan.pdf 2M -- -dColorImageResolution=100

-preset slow takes longer and gives a better picture at the same size.

Needs

ImageMagick for images, ffmpeg for video and Ghostscript for PDF. You only need the one for the files you shrink. shrink uses magick from ImageMagick 7, or convert from ImageMagick 6.

Examples

A photo for a form

$ shrink photo.jpg 500K
photo.jpg -> photo-small.jpg (4.8MB -> 488KB, quality 75, 55% wide, 3.2s)

Every photo in a folder, no wider than 1920

$ shrink -s 1M -w 1920 *.jpg
IMG_4410.jpg -> IMG_4410-small.jpg (5.1MB -> 702KB, quality 85, 0.8s)
IMG_4411.jpg -> IMG_4411-small.jpg (4.6MB -> 655KB, quality 85, 0.8s)
beach.jpg is already 610KB, which fits 1MB. Nothing written.

A screen recording for chat

$ shrink -v demo.mp4 25M
shrink: demo.mp4: video, 3:10, 148MB
shrink: bitrate: 25MB over 190s, less 96k for sound, is 974k
+ ffmpeg -nostdin -y -hide_banner -loglevel error -i demo.mp4 -c:v libx264 -preset medium -b:v 974k -pass 1 -passlogfile ./.shrink-Xq2c9L/pass -an -f null /dev/null
+ ffmpeg -nostdin -y -hide_banner -loglevel error -i demo.mp4 -c:v libx264 -preset medium -b:v 974k -pass 2 -passlogfile ./.shrink-Xq2c9L/pass -c:a aac -b:a 96k -movflags +faststart demo-small.mp4
demo.mp4 -> demo-small.mp4 (148MB -> 24MB, 974k, 2 passes, 1m52s)

A scanned PDF

$ shrink scan.pdf 4K
shrink: scan.pdf: /printer gives 10KB, trying the next
scan.pdf -> scan-small.pdf (5.9KB -> 3.1KB, /ebook, 0.1s)

A target out of reach

$ shrink -v scan.pdf 1K
+ gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/printer -sOutputFile=./.shrink-cz0B8F/try.pdf scan.pdf
shrink: scan.pdf: /printer gives 10KB, trying the next
+ gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -sOutputFile=./.shrink-cz0B8F/try.pdf scan.pdf
shrink: scan.pdf: /ebook gives 3.1KB, trying the next
+ gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -sOutputFile=./.shrink-cz0B8F/try.pdf scan.pdf
shrink: scan.pdf: /screen gives 3.1KB, over 1KB
shrink: wrote nothing. The smallest Ghostscript gets for scan.pdf is 3.1KB, with /ebook

Already small enough

$ shrink scan.pdf 1M
scan.pdf is already 5.9KB, which fits 1MB. Nothing written.

Troubleshooting

shrink: wrote nothing. The smallest ImageMagick gets for X is S, at 10% wide

The target is too small for that image even at a tenth of its width. Try a larger target, or another format such as WebP with -o photo.webp.

shrink: 1MB is too small for 9:42 of video, it leaves under 50k a second for the picture

Cut the clip first, or ask for more room. As a guide, 1 minute of 720p video looks fine at about 10 MB.

shrink: X is not an image, a video or a PDF

The ending is unknown and file did not recognise the content either.

The copy of a PNG screenshot is blurry

PNG has no quality setting, so shrink had to make it narrower. Try -o shot.webp or -o shot.jpg. Both come out much smaller at full width.

Exit status

See also

togif, magick(1), ffmpeg(1), gs(1)