I have not downloaded the app, so I don't know what it contains. The licenses for both ffmpeg and ImageMagick do not require anyone to mention them in the webs

I have not downloaded the app, so I don't know what it contains. The licenses for both ffmpeg and ImageMagick do not require anyone to mention them in the website. However, if they are being re-distributed, there are clear obligations for providing source code and attributions. Omitting to do so is a violation of the legal obligations.