1. Adds hardware_frames_constraints to retrieve valid HWPixelFormats and SWPixelFormats for specific hardware frame configurations. (#151)

2. Implements a HardwareFramesConstraints method in hardware_device_context to obtain these constraints for a given hardware frames context.

hardware_frames_constraints.go

@@ -0,0 +1,70 @@
+package astiav
+
+//#include <libavutil/hwcontext.h>
+import "C"
+import "unsafe"
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html
+type HardwareFramesConstraints struct {
+	c *C.AVHWFramesConstraints
+}
+
+func newHardwareFramesConstraintsFromC(c *C.AVHWFramesConstraints) *HardwareFramesConstraints {
+	if c == nil {
+		return nil
+	}
+	return &HardwareFramesConstraints{c: c}
+}
+
+func (hfc *HardwareFramesConstraints) pixelFormats(formats *C.enum_AVPixelFormat) (o []PixelFormat) {
+	if formats == nil {
+		return nil
+	}
+	size := unsafe.Sizeof(*formats)
+	for i := 0; ; i++ {
+		p := *(*C.int)(unsafe.Pointer(uintptr(unsafe.Pointer(formats)) + uintptr(i)*size))
+		if p == C.AV_PIX_FMT_NONE {
+			break
+		}
+		o = append(o, PixelFormat(p))
+	}
+	return
+}
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html#a4258bbe81f927b76b7ca5af44ba7ef6b
+func (hfc *HardwareFramesConstraints) ValidHardwarePixelFormats() (o []PixelFormat) {
+	return hfc.pixelFormats(hfc.c.valid_hw_formats)
+}
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html#aabea88093c6f85d6185ffb0852a2217f
+func (hfc *HardwareFramesConstraints) ValidSoftwarePixelFormats() (o []PixelFormat) {
+	return hfc.pixelFormats(hfc.c.valid_sw_formats)
+}
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html#af220776925452091085139081d5d7251
+func (hfc *HardwareFramesConstraints) MinWidth() int {
+	return int(hfc.c.min_width)
+}
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html#a3f1aec6d1c90f77837875c2a3598be46
+func (hfc *HardwareFramesConstraints) MinHeight() int {
+	return int(hfc.c.min_height)
+}
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html#a34e06e3397af2b83de9d78f893bf4168
+func (hfc *HardwareFramesConstraints) MaxWidth() int {
+	return int(hfc.c.max_width)
+}
+
+// https://ffmpeg.org/doxygen/7.0/structAVHWFramesConstraints.html#af5d3a683727f7b92abca7b7114d4e15c
+func (hfc *HardwareFramesConstraints) MaxHeight() int {
+	return int(hfc.c.max_height)
+}
+
+// https://ffmpeg.org/doxygen/7.0/hwcontext_8c.html#a29da7fa7ffa73266d1cbfccb116ed634
+func (hfc *HardwareFramesConstraints) Free() {
+	if hfc.c != nil {
+		C.av_hwframe_constraints_free(&hfc.c)
+		hfc.c = nil
+	}
+}