Say one develops a closed source app that can produce a file of its own format like .ll .Then one asks the user to run a GPL licenced batch script that uses ffmpeg(GPL) to do the final bit. Note that ffmpeg or the batch script is not distributed with the software but install instructions are there in the software. Will the software have to be GPL?


1 Answer 1


Will the software have to be GPL?

That depends on how closely your software depends on the post-processing by ffmpeg in particular.

If ffmpeg is just one of potentially many (independently developed) programs that can read and process the files your app creates, then your app is a separate and independent work from ffmpeg as far as copyright is concerned and that means both works can be licensed completely independently.

If your app uses intimate knowledge of how ffmpeg works and uses this file format to communicate complex, ffmpeg-specific data structures, then most likely your app will be considered a derived work of ffmpeg and needs to be under the GPL itself as well.

The question as to who invokes ffmpeg (the app itself or the user of the app) I find less relevant. Just the fact that it is two executables is relevant for the determination if the GPL applies.

  • Basically if it is an app that can make gifs and due to some reason making mp4 is not possible so the user is instructed to make mp4 using ffmpeg using a batch file. Oct 18, 2020 at 14:16
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    @compenthusiast, that is two independent programs then. One that creates animated GIFs (which can be used in their own right) and a second one that can convert an animated GIF into an MP4. That matches the first case I outlined. Oct 18, 2020 at 14:20
  • I know it should be understood but many people fear one mistake and GPL will release their source. Oct 18, 2020 at 14:21
  • @compenthusiast IANAL, but when you read the GPL, the main consequence of violating it seems to be that you lose all rights given to you by that license. That in itself doesn't necessarily mean you'll be forced to release the source. What it does mean however, is that you're no longer allowed to copy, modify or distribute the covered work. In addition to that, the original author could potentially sue you for copyright infringement.
    – Felix G
    Oct 19, 2020 at 9:02
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    I think it would be more likely that instead of filing a lawsuit, they'd ask you to either comply with the GPL or else stop distributing their software (i.e. completely remove it from your code). I don't know if you could actually be forced to open source your code, so i guess we would need a lawyer to answer that one.
    – Felix G
    Oct 19, 2020 at 12:13

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