Scale watermark overlay by video size with ffmpeg

Assuming a linux environment (or cygwin on windows), the only way I found is to execute 2 commands.

First to get main video size and perform math on them (note: x/20 == x*0.05:

val=`ffmpeg.exe -i 1.mp4 2>&1 | grep Video: | sed 's_.*, \([0-9]*x[0-9]*\) .*_\1_' | awk 'BEGIN {FS="x"} {print int($1/20)"x"int($2/20)}'`

Second to scale and overlay the video

ffmpeg -i 1.mp4 -i logo.png -filter_complex "[1:v] scale=$val [logo1]; [0:v][logo1] overlay=0:0" -y -b 1600k -c:v libx264 -profile high -level 4.1 -c:a libfaac -q:a 128k 2.mp4

Also, you could just replace $val on second line with the first expression (including backquotes) and get the same result, but I find it a little easier to read splitting command in two.

This can now be performed directly using the scale2ref filter.

ffmpeg -i 1.mp4 -i logo.png \
-filter_complex "[1:v][0:v]scale2ref=iw*0.05:-1[logo1][base]; \
 [base][logo1]overlay=0:0[v]" \
-map [v] -map 0:a -y -b:v 1600k -c:v libx264 -profile high -level 4.1 \
-c:a libfaac -b:a 128k 2.mp4