Add a GenericHwAccelRenderer for unknown hwaccels

This will get us limited hardware acceleration even for hwaccels
that we don't know about yet.

app/streaming/video/ffmpeg-renderers/genhwaccel.cpp

@@ -0,0 +1,77 @@
+#include "genhwaccel.h"
+
+GenericHwAccelRenderer::GenericHwAccelRenderer(AVHWDeviceType hwDeviceType)
+    : m_HwDeviceType(hwDeviceType),
+      m_HwContext(nullptr)
+{
+
+}
+
+GenericHwAccelRenderer::~GenericHwAccelRenderer()
+{
+    if (m_HwContext != nullptr) {
+        av_buffer_unref(&m_HwContext);
+    }
+}
+
+bool GenericHwAccelRenderer::initialize(PDECODER_PARAMETERS)
+{
+    int err;
+
+    err = av_hwdevice_ctx_create(&m_HwContext, m_HwDeviceType, nullptr, nullptr, 0);
+    if (err != 0) {
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                     "av_hwdevice_ctx_create(%u) failed: %d",
+                     m_HwDeviceType,
+                     err);
+        return false;
+    }
+
+    return true;
+}
+
+bool GenericHwAccelRenderer::prepareDecoderContext(AVCodecContext* context, AVDictionary**)
+{
+    context->hw_device_ctx = av_buffer_ref(m_HwContext);
+
+    SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
+                "Using generic FFmpeg hwaccel backend (type: %u). Performance may not be optimal!",
+                m_HwDeviceType);
+
+    return true;
+}
+
+void GenericHwAccelRenderer::renderFrame(AVFrame*)
+{
+    // We only support indirect rendering
+    SDL_assert(false);
+}
+
+bool GenericHwAccelRenderer::needsTestFrame()
+{
+    return true;
+}
+
+bool GenericHwAccelRenderer::isDirectRenderingSupported()
+{
+    // We only support rendering via read-back
+    return false;
+}
+
+int GenericHwAccelRenderer::getDecoderCapabilities()
+{
+    bool ok;
+    int caps = qEnvironmentVariableIntValue("GENHWACCEL_CAPS", &ok);
+    if (ok) {
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                    "Using GENHWACCEL_CAPS for decoder capabilities: %x",
+                    caps);
+    }
+    else {
+        SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                    "Assuming default decoder capabilities. Set GENHWACCEL_CAPS to override.");
+        caps = 0;
+    }
+
+    return caps;
+}

app/streaming/video/ffmpeg-renderers/genhwaccel.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include "renderer.h"
+
+class GenericHwAccelRenderer : public IFFmpegRenderer
+{
+public:
+    GenericHwAccelRenderer(AVHWDeviceType hwDeviceType);
+    virtual ~GenericHwAccelRenderer() override;
+    virtual bool initialize(PDECODER_PARAMETERS) override;
+    virtual bool prepareDecoderContext(AVCodecContext* context, AVDictionary** options) override;
+    virtual void renderFrame(AVFrame* frame) override;
+    virtual bool needsTestFrame() override;
+    virtual bool isDirectRenderingSupported() override;
+    virtual int getDecoderCapabilities() override;
+
+private:
+    AVHWDeviceType m_HwDeviceType;
+    AVBufferRef* m_HwContext;
+};
+