Use ffmpeg to center crop and scale an image to 1:1

frames.sh

#Given a video of any aspect ratio this script will extract center cropped thumbnails at 299x299.
#Useful for gathering image training data.
#Assumes ffmpeg 3.3.2
#If you get an error about exact that means you are using an older version of ffmpeg
#Simply remove the :exact=1. 
#This will make it work, but may cause the output size to be off by a pixel
#Script assumes you are downsampling. 

#!/bin/bash

PATH_TO_VID=myvideo.mov
PATH_TO_OUT_DIR=out
ffmpeg -i "$PATH_TO_VID" -y -an -q 0 -vf scale="'if(gt(iw,ih),-1,299):if(gt(iw,ih),299,-1)', crop=299:299:exact=1" $PATH_TO_OUT_DIR/%06d.jpg

Can you help me understand how to crop to 18.5:9? THank you

Here's a modified version that let's you specify the aspect ratio. I've set it to 18.5:9 for you.

#!/bin/bash

ASPECT_RATIO=`echo '18.5 / 9' | bc -l`
OUTPUT_WIDTH=400
OUTPUT_HEIGHT=`echo "$OUTPUT_WIDTH / $ASPECT_RATIO" | bc -l`
PATH_TO_VID=test.mov
PATH_TO_OUT_DIR=out

SCALE="'if(gte($ASPECT_RATIO, iw/ih), $OUTPUT_WIDTH, -1):if(gte($ASPECT_RATIO, iw/ih), -1, $OUTPUT_HEIGHT)', crop=$OUTPUT_WIDTH:$OUTPUT_HEIGHT:exact=1"
ffmpeg -i "$PATH_TO_VID" -y -an -q 0 -vf scale="$SCALE" $PATH_TO_OUT_DIR/%06d.jpg

ty

How can I crop the aspect ratio out of the video frame to give an exclusive fullscreen? For example, I have a video that has a smaller height than my display, I want to crop left and right so that the height matches that of my display. Also I may come across a video that has height greater than my display, so the top/bottom needs cropped.

Basically, I'm trying to eliminate scaling as the image is more crisp when being cropped instead of being scaled down. And in this instance Im trying to crop 16:9 out of a 1920x800 video and scale that to 1920x1080. Or whatever resolution the device may be.

That should be what the script does. Just change the OUTPUT_WIDTH to 1920. To be clear that will cause some upscaling since the extra 280 (1080-800) pixels (height) have to come from somewhere. If you don’t want to scale your only other option is letterboxing.

ok ty