feat(rife): add support for frame interpolation and RIFE (#1244)

* feat: add RIFE files and processor/interpolator abstractions
* feat: add `rife` as processor option
* feat: add frame interpolation math except first frame
* feat: complete motion interpolation and add scene detection
* feat: improve Vulkan device validation
* fix: fix casting issues and variable names
* refactor: improve error-checking; add abstractions and factories
* refactor: improve readability of the frames processor
* docs: update changelog

Signed-off-by: k4yt3x <i@k4yt3x.com>

include/libvideo2x/processor.h

@@ -0,0 +1,45 @@
+#ifndef PROCESSOR_H
+#define PROCESSOR_H
+
+#include <vector>
+
+extern "C" {
+#include <libavcodec/avcodec.h>
+#include <libavfilter/avfilter.h>
+#include <libavutil/buffer.h>
+}
+
+#include "libvideo2x.h"
+
+class Processor {
+   public:
+    virtual ~Processor() = default;
+    virtual int init(AVCodecContext *dec_ctx, AVCodecContext *enc_ctx, AVBufferRef *hw_ctx) = 0;
+    virtual int flush(std::vector<AVFrame *> &_) { return 0; }
+    virtual ProcessingMode get_processing_mode() const = 0;
+    virtual ProcessorType get_processor_type() const = 0;
+    virtual void get_output_dimensions(
+        const ProcessorConfig *processor_config,
+        int in_width,
+        int in_height,
+        int &width,
+        int &height
+    ) const = 0;
+};
+
+// Abstract base class for filters
+class Filter : public Processor {
+   public:
+    ProcessingMode get_processing_mode() const override { return PROCESSING_MODE_FILTER; }
+    virtual int filter(AVFrame *in_frame, AVFrame **out_frame) = 0;
+};
+
+// Abstract base class for interpolators
+class Interpolator : public Processor {
+   public:
+    ProcessingMode get_processing_mode() const override { return PROCESSING_MODE_INTERPOLATE; }
+    virtual int
+    interpolate(AVFrame *prev_frame, AVFrame *in_frame, AVFrame **out_frame, float time_step) = 0;
+};
+
+#endif  // PROCESSOR_H