Scale, crop and trim videos for Snapchat

snapchat.sh

#!/bin/bash

# this script does four things:
#
#   1. detects any crop marks (black bars) on the source clip
#   2. uses those crop marks to trim the clip so it has no bars (semi-manual task)
#   3. scales the video up ands crops it (from the center) to snapchat size
#   4. trims the clip to 10s long (might make sense to do this step first?)

INPUT='vid.mp4'
DUMMY='dummy.avi'
TMP='tmp.mp4'
CROPPED='cropped.mp4'
OUTPUT='out.mp4'
DESIRED_WIDTH=1080
DESIRED_HEIGHT=1920
START_TIMECODE=00:00:00.0
CLIP_LENGTH=00:00:10.0

# 1. detect the crop marks (numbers here are tolerance levels for detecting black bars)
ffmpeg -i $INPUT -vf "cropdetect=24:16:0" $DUMMY

printf "
######################

 What was the crop?

 For example, for this output:

    [Parsed_cropdetect_0 @ 0x7fca9bc214a0] x1:0 x2:639 y1:0 y2:359 w:640 h:352 x:0 y:4 pts:51984 t:86.640000 crop=640:352:0:4

 the crop value is:

    640:352:0:4

######################

Type the crop value and press Enter: "
read CROP_VALUES

# 2. crop the video to cut out those black bars:
ffmpeg -i $INPUT -filter:v "crop=$CROP_VALUES" -c:a copy $TMP

# 3. now scale it up and crop it to correct size
ffmpeg -i $TMP -filter:v "scale=iw*$DESIRED_HEIGHT/ih:$DESIRED_HEIGHT, crop=$DESIRED_WIDTH:$DESIRED_HEIGHT" -c:a copy $CROPPED

# 4. finally, trim the clip to the desired length
ffmpeg -i $CROPPED -ss $START_TIMECODE -t $CLIP_LENGTH $OUTPUT

# cleanup tmp files
rm $DUMMY $TMP $CROPPED

how do i run this script?