Merge pull request #27453 from MELSunny:4.x

Add Raspberry Pi 4 and 5 V4L2 Stateless HEVC Hardware Acceleration with FFmpeg #27453

This PR enables V4L2 stateless HEVC hardware acceleration for Raspberry Pi 5 within OpenCV's videoio module. It leverages FFmpeg's drm acceleration ([FFmpeg API changes](ee1f79b0fa/doc/APIchanges (L1529))), significantly improving HEVC decoding performance on RPi5 for robotics and embedded vision applications.

I have a working proof-of-concept with local benchmarks showing clear gains.

Checklist Status:

Ready: License, branch (4.x), FFmpeg reference, and (linked) related issue (#27452).
Seeking Guidance: Need help with formal C++ performance/accuracy tests, opencv_extra integration, and full documentation/examples.
As a Python developer, I welcome C++ best practice feedback and assistance with testing setup.

### Pull Request Readiness Checklist

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

- [x] I agree to contribute to the project under Apache 2 License.
- [x] 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
- [x] The PR is proposed to the proper branch
- [x] 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

modules/videoio/include/opencv2/videoio.hpp

@@ -268,6 +268,7 @@ enum VideoAccelerationType
     VIDEO_ACCELERATION_D3D11    =  2,  //!< DirectX 11
     VIDEO_ACCELERATION_VAAPI    =  3,  //!< VAAPI
     VIDEO_ACCELERATION_MFX      =  4,  //!< libmfx (Intel MediaSDK/oneVPL)
+    VIDEO_ACCELERATION_DRM       =  5,  //!< Raspberry Pi V4
 };
 
 //! @} Hardware acceleration support

modules/videoio/src/cap_ffmpeg_hw.hpp

@@ -57,6 +57,9 @@ extern "C" {
 #ifdef HAVE_MFX // dependency only on MFX header files, no linkage dependency
 #include <libavutil/hwcontext_qsv.h>
 #endif
+#ifdef HAVE_DRM
+#include <libavutil/hwcontext_drm.h>
+#endif
 }
 
 #define HW_DEFAULT_POOL_SIZE    32
@@ -81,6 +84,7 @@ const char* getVideoAccelerationName(VideoAccelerationType va_type)
     case VIDEO_ACCELERATION_D3D11: return "d3d11";
     case VIDEO_ACCELERATION_VAAPI: return "vaapi";
     case VIDEO_ACCELERATION_MFX: return "mfx";
+    case VIDEO_ACCELERATION_DRM : return "drm";
     }
     return "unknown";
 }
@@ -119,6 +123,7 @@ std::string getDecoderConfiguration(VideoAccelerationType va_type, AVDictionary
     case VIDEO_ACCELERATION_D3D11: return "";
     case VIDEO_ACCELERATION_VAAPI: return "vaapi.iHD";
     case VIDEO_ACCELERATION_MFX: return "qsv.iHD";
+    case VIDEO_ACCELERATION_DRM: return "drm";
     }
     return "";
 #endif
@@ -158,6 +163,8 @@ std::string getEncoderConfiguration(VideoAccelerationType va_type, AVDictionary
     case VIDEO_ACCELERATION_D3D11: return "";
     case VIDEO_ACCELERATION_VAAPI: return "vaapi.iHD";
     case VIDEO_ACCELERATION_MFX: return "qsv.iHD";
+    case VIDEO_ACCELERATION_DRM: return "";
+    // Raspberry Pi 5 has no encoders, so we don't support it
     }
     return "unknown";
 #endif
@@ -236,6 +243,18 @@ bool hw_check_device(AVBufferRef* ctx, AVHWDeviceType hw_type, const std::string
             dxgiDevice->Release();
         }
     }
+#endif
+#if defined(HAVE_DRM)
+    if (hw_device_ctx->type == AV_HWDEVICE_TYPE_DRM) {
+        AVDRMDeviceContext *drm_ctx = (AVDRMDeviceContext *)hw_device_ctx->hwctx;
+        if (drm_ctx->fd >= 0) {
+            drmVersionPtr drm_version = drmGetVersion(drm_ctx->fd);
+            if (drm_version) {
+                device_name = drm_version->name;
+                drmFreeVersion(drm_version);
+            }
+        }
+    }
 #endif
     if (hw_device_ctx->type == AV_HWDEVICE_TYPE_VAAPI) {
 #if defined(HAVE_VA) && (VA_MAJOR_VERSION >= 1)
@@ -908,6 +927,7 @@ VideoAccelerationType hw_type_to_va_type(AVHWDeviceType hw_type) {
             { AV_HWDEVICE_TYPE_VAAPI, VIDEO_ACCELERATION_VAAPI },
             { AV_HWDEVICE_TYPE_QSV, VIDEO_ACCELERATION_MFX },
             { AV_HWDEVICE_TYPE_CUDA, (VideoAccelerationType)(1 << 11) },
+            { AV_HWDEVICE_TYPE_DRM, VIDEO_ACCELERATION_DRM }
     };
     for (const HWTypeFFMPEG& hw : known_hw_types) {
         if (hw_type == hw.hw_type)

modules/videoio/src/cap_interface.hpp

@@ -417,6 +417,7 @@ std::ostream& operator<<(std::ostream& out, const VideoAccelerationType& va_type
     case VIDEO_ACCELERATION_D3D11: out << "D3D11"; return out;
     case VIDEO_ACCELERATION_VAAPI: out << "VAAPI"; return out;
     case VIDEO_ACCELERATION_MFX: out << "MFX"; return out;
+    case VIDEO_ACCELERATION_DRM: out << "DRM"; return out;
     }
     out << cv::format("UNKNOWN(0x%ux)", static_cast<unsigned int>(va_type));
     return out;

modules/videoio/test/test_precomp.hpp

@@ -35,6 +35,7 @@ std::ostream& operator<<(std::ostream& out, const VideoAccelerationType& va_type
             {VIDEO_ACCELERATION_D3D11, "D3D11"},
             {VIDEO_ACCELERATION_VAAPI, "VAAPI"},
             {VIDEO_ACCELERATION_MFX,   "MFX"},
+            {VIDEO_ACCELERATION_DRM,   "DRM"},
     };
     for (const auto& va : va_types) {
         if (va_type == va.va_type) {

modules/videoio/test/test_video_io.cpp

@@ -871,6 +871,7 @@ static const VideoAccelerationType hw_types[] = {
         VIDEO_ACCELERATION_D3D11,
 #else
         VIDEO_ACCELERATION_VAAPI,
+        VIDEO_ACCELERATION_DRM,
 #endif
 };
 

samples/tapi/video_acceleration.cpp

@@ -42,6 +42,7 @@ struct {
     { VIDEO_ACCELERATION_D3D11, "d3d11" },
     { VIDEO_ACCELERATION_VAAPI, "vaapi" },
     { VIDEO_ACCELERATION_MFX, "mfx" },
+    { VIDEO_ACCELERATION_DRM, "drm" },
 };
 
 class FPSCounter {