[FFmpeg-user] Applying the LGPL to ffmpeg usage

Carl Zwanzig cpz at tuunq.com
Tue Nov 3 20:01:48 EET 2020

(changed the subject line)

On 11/1/2020 12:07 PM, Carl Eugen Hoyos wrote:

> If the question is "am I allowed to distribute a binary based on (L)GPL
> software" then the answer does not depend on static or dynamic linking.

That's not clear (to me), please point me to the relevant section of the 
LGPL and describe how it applies.

> Am Mo., 26. Okt. 2020 um 06:44 Uhr schrieb Carl Zwanzig <cpz at tuunq.com>: >> There are cases where you can share a dynamic build (no GPL parts) that
>> links to non-free libraries but not a static build. (I think building with
>> BMD Decklink support is in that catagory.)

> No.
That is not clear what it refers to.

> Decklink is not GPL-compatible.

We know that the BMD code itself is not _GPL_ compatible (although the 
headers & api appear to be), but when ffmpeg is built with NO GPL the LGPL 
would apply. By my understanding of that license, you can both dynamically 
link -to- LGPL code from proprietary code and link -from- the LGPL code to 
proprietary*. The only questions is whether ffmpeg's CLI front-end is 
considered a "library" for the purposes of the license and how the 
proprietary parts are distributed.

*Note- that does not, and should not, imply that the libraries are being 
_distributed_ together.

It would certainly be compliant to write one's own code and dynamically link 
to both LGPL and proprietary libraries (and to distribute the result), and 
that appears to be commonly accepted by other opensource projects (e.g OBS, 
CasparCG, MLT, etc; they have plugins for both BMD and NewTek NDI).

If any of that is not correct, please point me to the parts of the LGPL, or 
guidance from the FSF, that cover it because I'm not finding anything.


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