ffmpeg.wasm and possible license problem

[ali4864]

The license of ffmpeg.wasm is MIT license, while ffmpeg.wasm is based on FFmpeg that it is licensed under LGPL version 2.0, based on my understanding, ffmpeg.wasm project is considered a derivative work that is based on FFmpeg and it must be licensed under a same license (LGPL). How has it been licensed under MIT?

[mmiscool]

I have questions about this too.
It seems that to comply with the FFmpeg licence there are 2 things required.

The binary for the wasm build needs to have the exact source tarbar and build options available upon request and those particular files would need to be marked with the licence for the FFmpeg project.

I am interested in using but don't want to anger the FFmpeg folks or get in to any hot water using this to build a web app.

[mmiscool]

Looking at the page https://www.ffmpeg.org/legal.html it has a licence compliance checklist.
My concern is related to steps 5 - 9 of the list. Are the build instructions and the exact tar ball available as part of the NPm package?

License Compliance Checklist

The following is a checklist for LGPL compliance when linking against the FFmpeg libraries. It is not the only way to comply with the license, but we think it is the easiest. There are also a few items that are not really related to LGPL compliance but are good ideas anyway.

1. Compile FFmpeg without "--enable-gpl" and without "--enable-nonfree".
2. Use dynamic linking (on windows, this means linking to dlls) for linking with FFmpeg libraries.
3. Distribute the source code of FFmpeg, no matter if you modified it or not.
4. Make sure the source code corresponds exactly to the library binaries you are distributing.
5. Run the command "git diff > changes.diff" in the root directory of the FFmpeg source code to create a file with only the changes.
6. Explain how you compiled FFmpeg, for example the configure line, in a text file added to the root directory of the source code.
7. Use tarball or a zip file for distributing the source code.
8. Host the FFmpeg source code on the same webserver as the binary you are distributing.
9. Add "This software uses code of FFmpeg licensed under the LGPLv2.1 and its source can be downloaded here" to every page in your website where there is a download link to your application.
10. Mention "This software uses libraries from the FFmpeg project under the LGPLv2.1" in your program "about box".
11. Mention in your EULA that your program uses FFmpeg under the LGPLv2.1.
12. If your EULA claims ownership over the code, you have to explicitly mention that you do not own FFmpeg, and where the relevant owners can be found.
13. Remove any prohibition of reverse engineering from your EULA.
14. Apply the same changes to all translations of your EULA.
15. Do not misspell FFmpeg (two capitals F and lowercase "mpeg").
16. Do not rename FFmpeg dlls to some obfuscated name, but adding a suffix or prefix is fine (renaming "avcodec.dll" to "MyProgDec.dll" is not fine, but to "avcodec-MyProg.dll" is).
17. Go through all the items again for any LGPL external library you compiled into FFmpeg (for example LAME).
18. Make sure your program is not using any GPL libraries (notably libx264).

[AlRodriguezGar14]

5. Run the command "git diff > changes.diff" in the root directory of the FFmpeg source code to create a file with only the changes.

You are right to be concerned, because it's not about MIT vs LGPL but MIT vs GPL, which is more restrictive and incompatible with MIT.

Compile FFmpeg without "--enable-gpl" and without "--enable-nonfree".

The Dockerfile builds with --enable-gpl
https://github.com/ffmpegwasm/ffmpeg.wasm/blob/main/Dockerfile

RUN bash -x /src/build.sh \
      --enable-gpl \
      --enable-libx264 \
      --enable-libx265 \
      --enable-libvpx \
      --enable-libmp3lame \
      --enable-libtheora \
      --enable-libvorbis \
      --enable-libopus \
      --enable-zlib \
      --enable-libwebp \
      --enable-libfreetype \
      --enable-libfribidi \
      --enable-libass \
      --enable-libzimg 

Also, package.json of ffmpeg/core and ffmpe/core-mt state that the license is GPL (far more restrictive than LGPL)

• https://github.com/ffmpegwasm/ffmpeg.wasm/blob/main/packages/core/package.json
• https://github.com/ffmpegwasm/ffmpeg.wasm/blob/main/packages/core-mt/package.json

If @ffmpeg/core is GPL-licensed, the MIT license on the wrapper is irrelevant. Any software distributing or linking against the GPL core must comply with GPL v2+ requirements, including source distribution.

[mmiscool]

is there a way that the source code tar and the compiler instructions could be tossed in to the NPM package in such a way that a simple function call could download the tar and return a string with the instructions.

It sounds to me like that would take care of any of the possible problems and allow people using the NPM package to easily be in compliance with the licence.

I do think there is some nuance since this is being compiled in such a way that it works similarly to the command line version and any applications using it are communicating with it using the stdin/out and accessing the virtual file system as if it is a separate application just like you would if you made a bash script that calls a prebuilt FFmpeg binary.

[AlRodriguezGar14]

@mmiscool I haven't explored that path, but it sounds like it could work for the source offer requirement. My approach is compiling to WASM myself without the --enable-gpl flag, and then using those builds with ffmpeg.load({ coreURL, wasmURL }).

Here's the base Makefile.wasm (Not production hardened. Also, you can build a lighter version only with the muxers, demuxers, parsers, decoders, and filters you want/need):

FFMPEG_SRC := ./ffmpeg-src
OUTPUT_DIR := ./public/wasm
NPROC := $(shell nproc 2>/dev/null || sysctl -n hw.ncpu 2>/dev/null || echo 4)

all:
	@command -v emcc >/dev/null 2>&1 || { echo "Error: emcc not found. Activate Emscripten SDK."; exit 1; }
	@test -d "$(FFMPEG_SRC)" || git clone --branch n7.1 --depth 1 https://git.ffmpeg.org/ffmpeg.git "$(FFMPEG_SRC)"
	cd "$(FFMPEG_SRC)" && emconfigure ./configure \
		--cc=emcc --cxx=em++ --ar=emar \
		--target-os=none --arch=wasm32 --cpu=generic \
		--enable-cross-compile \
		--disable-x86asm --disable-asm \
		--disable-doc --disable-network --disable-autodetect --disable-debug \
		--disable-gpl --disable-version3 \
		--extra-ldflags="-sWASM=1 -sMODULARIZE=1 -sEXPORT_NAME=\"FFmpegCore\" -sALLOW_MEMORY_GROWTH=1"
	cd "$(FFMPEG_SRC)" && emmake make -j$(NPROC) ffmpeg
	mkdir -p "$(OUTPUT_DIR)"
	cp "$(FFMPEG_SRC)/ffmpeg" "$(OUTPUT_DIR)/ffmpeg-core.js"
	cp "$(FFMPEG_SRC)/ffmpeg.wasm" "$(OUTPUT_DIR)/ffmpeg-core.wasm"

clean:
	rm -rf "$(OUTPUT_DIR)"

Then, in your worker:

  await ffmpeg.load({
    coreURL: '/wasm/ffmpeg-core.js',
    wasmURL: '/wasm/ffmpeg-core.wasm',
  })