Introduce libavdevice to make v4l2 available to the ffmpeg backend by kallaballa · Pull Request #22706 · opencv/opencv

kallaballa · 2022-10-27T00:43:21Z

The pertaining issue: #22705

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

I agree to contribute to the project under Apache 2 License.
To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
The PR is proposed to the proper branch
There is a reference to the original bug report and related work
There is accuracy test, performance test and test data in opencv_extra repository, if applicable
Patch to opencv_extra has the same branch name.
The feature is well documented and sample code can be built with the project CMake

alalek · 2022-10-28T09:08:26Z

modules/videoio/cmake/detect_ffmpeg.cmake

 set(_used_ffmpeg_libraries ${_required_ffmpeg_libraries})
 if(NOT HAVE_FFMPEG AND PKG_CONFIG_FOUND)
-  ocv_check_modules(FFMPEG libavcodec libavformat libavutil libswscale)
+  ocv_check_modules(FFMPEG libavcodec libavformat libavutil libswscale libavdevice)


Need to check if libavdevice module is optional or not in FFmpeg and libav packages.
If it is optional, then it should be added as optional into OpenCV (to avoid breaking of existed user configurations)

Update:

Looks like some configurations may miss libavdevice:

E.g., Ubuntu 20.04:

# ll /usr/lib/x86_64-linux-gnu/pkgconfig/{libav*,libswscale*} -rw-r--r-- 1 root root 742 May 18 21:24 /usr/lib/x86_64-linux-gnu/pkgconfig/libavcodec.pc -rw-r--r-- 1 root root 472 May 18 21:24 /usr/lib/x86_64-linux-gnu/pkgconfig/libavformat.pc -rw-r--r-- 1 root root 386 May 18 21:24 /usr/lib/x86_64-linux-gnu/pkgconfig/libavutil.pc -rw-r--r-- 1 root root 322 May 18 21:24 /usr/lib/x86_64-linux-gnu/pkgconfig/libswscale.pc

Installed through apt-get install libavcodec-dev libavformat-dev libswscale-dev (current configuration on CI)

Optional dependency means these steps:

CMake cache variable to control behavior - OPENCV_FFMPEG_ENABLE_LIBAVDEVICE

default value is OFF (to avoid breaking of user code)

add compiler macro to pass into C++ code if libavdevice enabled and should be used (e.g., OPENCV_FFMPEG_LIBAVDEVICE=1)

related C++ code should be guarded by #ifdef OPENCV_FFMPEG_LIBAVDEVICE

Thanks! makes sense. I am on it.

Just about the first step. Shouldn't i do it like that?

and then like that?

I think i figured it out right: eb7bc8e

modules/videoio/cmake/detect_ffmpeg.cmake

alalek

Thank you for update!

alalek · 2022-11-08T21:26:55Z

modules/videoio/CMakeLists.txt

+if(FFMPEG_libavdevice_FOUND)
+      add_definitions(-DHAVE_FFMPEG_LIBAVDEVICE)
+endif()
+


add_definitions

Definition should go through target. Need to patch this line instead:

ocv_add_external_target(ffmpeg "${FFMPEG_INCLUDE_DIRS}" "${FFMPEG_LIBRARIES}" "HAVE_FFMPEG")

alalek · 2022-11-08T21:29:57Z

modules/videoio/cmake/detect_ffmpeg.cmake

+    ocv_check_modules(FFMPEG_libavdevice libavdevice) # optional
+    if(FFMPEG_libavdevice_FOUND)
+      list(APPEND FFMPEG_LIBRARIES ${FFMPEG_libavdevice_LIBRARIES})
+      list(APPEND _used_ffmpeg_libraries libavdevice)
+  endif()


Broken indentation.

Please add OPENCV_FFMPEG_ENABLE_LIBAVDEVICE pre-check to keep it configurable.
Keep value is OFF by default to preserve compatibility in current 4.x branch.
ON default value could be added separately for 5.x branch only.

I understand.

ON default value could be added separately for 5.x branch only.

Created a separate branch rebased to 5.x with default value 'ON'.
Gonna create a pull request once this is through.

After merge to "4.x" these changes would be propagated to "5.x" branch in 1-3 weeks: https://github.com/opencv/opencv/wiki/Branches
Patch would be simple after that.

I understand.

… through ocv_add_external_target

alalek

Overall looks good!

alalek · 2022-11-09T23:20:12Z

CMakeLists.txt

+OCV_OPTION(OPENCV_FFMPEG_ENABLE_LIBAVDEVICE "Include FFMPEG/libavdevice library support." OFF
+  VISIBLE_IF WITH_FFMPEG)


Lets move it to the top of modules/videoio/cmake/detect_ffmpeg.cmake

This list is for high level configuration, "fine" tuning should go separately.

…make

kallaballa · 2022-11-11T22:28:47Z

Great! Thx!

…g_v4l2 Introduce libavdevice to make v4l2 available to the ffmpeg backend * introduce libavdevice to make v4l2 available to the ffmpeg backend * downgrade the min required libavdevice version to 53.2.0 * make libavdevice optional * create OCV_OPTION OPENCV_FFMPEG_ENABLE_LIBAVDEVICE and add definition through ocv_add_external_target * move OCV_OPTION 'OPENCV_FFMPEG_ENABLE_LIBAVDEVICE' to detect_ffmpeg.cmake

introduce libavdevice to make v4l2 available to the ffmpeg backend

ab6adab

asmorkalov added category: videoio category: videoio(camera) labels Oct 27, 2022

alalek reviewed Oct 28, 2022

View reviewed changes

kallaballa added 2 commits October 30, 2022 10:53

downgrade the min required libavdevice version to 53.2.0

907c884

make libavdevice optional

eb7bc8e

alalek reviewed Nov 8, 2022

View reviewed changes

kallaballa added 2 commits November 9, 2022 18:05

Merge branch 'opencv:4.x' into libavdevice_for_ffmpeg_v4l2

828d893

create OCV_OPTION OPENCV_FFMPEG_ENABLE_LIBAVDEVICE and add definition…

caec0b0

… through ocv_add_external_target

alalek reviewed Nov 9, 2022

View reviewed changes

move OCV_OPTION 'OPENCV_FFMPEG_ENABLE_LIBAVDEVICE' to detect_ffmpeg.c…

50ff22a

…make

alalek approved these changes Nov 11, 2022

View reviewed changes

alalek merged commit da4ac6b into opencv:4.x Nov 11, 2022

alalek mentioned this pull request Jan 8, 2023

(5.x) Merge 4.x #23113

Merged

SpaceIm mentioned this pull request Aug 14, 2023

Bump opencv/4.8.1 conan-io/conan-center-index#19194

Merged

3 tasks

This was referenced Sep 28, 2025

VideoCapture using CAP_FFMPEG to capture the camera device #26812

Closed

Open camera device by index through FFmpeg #27841

Merged

		OCV_OPTION(OPENCV_FFMPEG_ENABLE_LIBAVDEVICE "Include FFMPEG/libavdevice library support." OFF
		VISIBLE_IF WITH_FFMPEG)

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kallaballa commented Oct 27, 2022 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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alalek Nov 8, 2022 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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kallaballa commented Nov 11, 2022

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kallaballa commented Oct 27, 2022 •

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alalek Oct 28, 2022 •

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alalek Nov 8, 2022 •

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