Build OpenCV with FFmpeg on Linux

[c-ewing]

Description

Due to the non-standard install location of FFmpeg during the AliceVision build OpenCV cannot find it. This patch adds FFmpeg to the BUILD_PREFIX of OpenCV to enable the FFmpeg features.

This builds on the work done in #1732 by @furbrain and @fabiencastan.

Features list

• Fix [bug] KeyframeSelection node not opening video Meshroom#2285

Implementation remarks

Expanding on #1732, OpenCV fetches a prebuilt FFmpeg when building for Windows but looks for system libraries when building on Linux.

OpenCV being built without FFmpeg is confirmed by building the Ubuntu docker image and running:

$ ./opt/AliceVision_install/bin-deps/opencv_version -v | grep -i ffmpeg

Which responds with NO.

OpenCV is picky about how external dependencies are specified and it does not support directly specifying install locations. Instead of specifying a location OpenCV's CMAKE uses find_package() to find packages. It first looks for Modules in CMAKE_MODULE_PATH, then looks within the OpenCV source for Find.cmake files according to the CMake Docs.

This implementation adds the FFmpeg install path to the ${CMAKE_PREFIX_PATH} of OpenCV, allowing find_package() to search in ${CMAKE_INSTALL_PREFIX} when building.

This change is confirmed by running opencv_version -v | grep -i ffmpeg, resulting in YES

[cbentejac]

Thanks for your contribution @c-ewing!

[ConejosFritos]

I am very sorry if the answer to my question appears very obvious to others but I cannot follow how am I supposed to implement this solution, are there any step by step instructions to be found for this implementation?

[c-ewing]

Hey there! I don't have any step by step instructions however the latest Alicevision docker images should be being built against this change. You can either pull the images from dockerhub or build the latest Alicevision from scratch using the docker files provided in the repo (this can take a *long* time). I'm not sure what your use case is but if you're looking to use this with Meshroom you'll have to modify your install as there is no version shipping with these changes.

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On Sun, Jan 5, 2025, 09:37 ConejosFritos ***@***.***> wrote: I am very sorry if the answer to my question appears very obvious to others but I cannot follow how am I supposed to implement this solution, are there any step by step instructions to be found for this implementation? — Reply to this email directly, view it on GitHub <#1784 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AODDSV3X4BEX5LSH3LSRC5L2JFUT7AVCNFSM6AAAAABSMR36NCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNZRGY4TQOBXG4> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[ConejosFritos]

ok, thank you very much, I was trying out Meshroom for 3d modeling but it appears to not only require a CUDA capable Nvidia GPU which I do not have in my linux Laptop, but also seams incomplete of certain features. I guess I will continue trying different Photogrametry apps for my modeling attempts