Overview

• add support for HW accelerated decode/encode in FFMPEG backend of VideoCapture and VideoWriter APIs under #ifdef check for FFMPEG version >= 3.4
• introduce new properties CAP_PROP_HW_ACCELERATION, CAP_PROP_HW_DEVICE, VIDEOWRITER_PROP_HW_ACCELERATION, VIDEOWRITER_PROP_HW_DEVICE and enum VideoAccelerationType.
• new properties supported in three HW-capable backends: ffmpeg, gstreamer, msmf
• setting new properties supported only via params parameter in VideoCapture/VideoWriter constructor or open() function, not supported in setProperty() call after open() call
• by default (if property not set) HW acceleration enabled in HW-capable backends for both VideoCapture and VideoWriter
• if HW accelerated decoder/encoder not found or failed to initilize, VideoCapture/VideoWriter gracefully falls back to SW decoder/encoder. Video acceleration status (HW or SW codec) could be queried via getProperty(CAP_PROP_HW_ACCELERATION) / getProperty(VIDEOWRITER_PROP_HW_ACCELERATION)
• new sample video_acceleration
• test iterating three backends and acceleration types

HW acceleration types support matrix, in priority order:

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 other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to 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