Refactoring to remove the FavouriteFormat static member

src/ffmpeg/avcodec.cpp

@@ -6,19 +6,6 @@ extern "C" {
 #include <string>
 
 namespace mgs::ffmpeg {
-namespace {
-::AVPixelFormat get_favourite_format_ifp (::AVCodecContext* s, const ::AVPixelFormat* fmt) {
-	const ::AVPixelFormat* curr_fmt = fmt;
-	const auto fav_format = static_cast<::AVPixelFormat>(Decoder::FavouriteFormat);
-	while (*curr_fmt != -1) {
-		if (*curr_fmt == fav_format)
-			return fav_format;
-		++curr_fmt;
-	}
-	return ::avcodec_default_get_format(s, fmt);
-}
-} //unnamed namespace
-
 AVCodec::AVCodec (::AVCodecID id) :
 	m_avcodec(::avcodec_find_decoder(id))
 {
@@ -28,7 +15,7 @@ AVCodec::AVCodec (::AVCodecID id) :
 
 AVCodec::~AVCodec() noexcept = default;
 
-Decoder AVCodec::make_decoder (unsigned int width, unsigned int height) {
+Decoder AVCodec::make_decoder (unsigned int width, unsigned int height, ::AVPixelFormat dst_format) {
 	::AVCodec* const codec = m_avcodec.get();
 	Decoder::UniqueAVCodecContext context{::avcodec_alloc_context3(codec)};
 	if (not context)
@@ -40,12 +27,11 @@ Decoder AVCodec::make_decoder (unsigned int width, unsigned int height) {
 
 	context->width = width;
 	context->height = height;
-	context->get_format = &get_favourite_format_ifp;
 
 	if (::avcodec_open2(context.get(), codec, nullptr) < 0)
 		throw std::runtime_error("Could not open codec");
 
-	return {std::move(context)};
+	return {std::move(context), dst_format};
 }
 
 } //namespace mgs::ffmpeg

src/ffmpeg/avcodec.hpp

@@ -4,6 +4,7 @@
 #include "avdeleter.hpp"
 extern "C" {
 #include <libavcodec/codec_id.h>
+#include <libavutil/pixfmt.h>
 } //extern C
 
 namespace mgs::ffmpeg {
@@ -14,7 +15,7 @@ public:
 	explicit AVCodec (::AVCodecID id);
 	~AVCodec() noexcept;
 
-	Decoder make_decoder (unsigned int width, unsigned int height);
+	Decoder make_decoder (unsigned int width, unsigned int height, ::AVPixelFormat dst_format);
 
 private:
 	unique_av_ptr<struct ::AVCodec> m_avcodec;

src/ffmpeg/decoder.cpp

@@ -12,16 +12,32 @@ extern "C" {
 namespace mgs::ffmpeg {
 namespace {
 constexpr int Align = 32;
+
+::AVPixelFormat get_favourite_format_ifp (::AVCodecContext* s, const ::AVPixelFormat* fmt) {
+	assert(s->opaque);
+
+	const ::AVPixelFormat* curr_fmt = fmt;
+	const auto fav_format = static_cast<const Decoder*>(s->opaque)->destination_format();
+	while (*curr_fmt != -1) {
+		if (*curr_fmt == fav_format)
+			return fav_format;
+		++curr_fmt;
+	}
+	return ::avcodec_default_get_format(s, fmt);
+}
+
 } //unnamed namespace
 
-const int Decoder::FavouriteFormat = static_cast<int>(::AVPixelFormat::AV_PIX_FMT_RGB24);
+Decoder::Decoder (UniqueAVCodecContext&& context, ::AVPixelFormat dst_format) :
-
-Decoder::Decoder (UniqueAVCodecContext&& context) :
 	m_context(std::move(context)),
 	m_packet(::av_packet_alloc()),
 	m_frame1(::av_frame_alloc()),
-	m_frame2(::av_frame_alloc())
+	m_frame2(::av_frame_alloc()),
+	m_dst_format(dst_format)
 {
+	assert(not m_context->opaque);
+	m_context->opaque = this;
+	m_context->get_format = &get_favourite_format_ifp;
 }
 
 Decoder::~Decoder() noexcept = default;
@@ -50,7 +66,7 @@ std::size_t Decoder::decode (const std::uint8_t* input, std::size_t input_size,
 		return 0;
 
 	const std::size_t new_out_size = ::av_image_get_buffer_size(
-		static_cast<::AVPixelFormat>(FavouriteFormat),
+		m_dst_format,
 		m_context->width,
 		m_context->height,
 		Align
@@ -69,12 +85,16 @@ std::size_t Decoder::decode (const std::uint8_t* input, std::size_t input_size,
 	const std::size_t out_size_safe = std::min(out_size, new_out_size);
 	std::copy(m_frame2->data[0], m_frame2->data[0] + out_size_safe, out);
 
-	return out_size_safe;
+	return new_out_size;
+}
+
+::AVPixelFormat Decoder::destination_format() const noexcept {
+	return m_dst_format;
 }
 
 void Decoder::init_sws_context() {
 	const std::size_t new_out_size = ::av_image_get_buffer_size(
-		static_cast<::AVPixelFormat>(FavouriteFormat),
+		m_dst_format,
 		m_context->width,
 		m_context->height,
 		Align
@@ -91,7 +111,7 @@ void Decoder::init_sws_context() {
 		m_context->pix_fmt, //AV_PIX_FMT_YUVJ422P, //AVPixelFormat src_format
 		m_context->width, //int dst_width
 		m_context->height, //int dst_height
-		static_cast<::AVPixelFormat>(FavouriteFormat), //AVPixelFormat dst_format
+		m_dst_format, //AVPixelFormat dst_format
 		SWS_FAST_BILINEAR, //int flags
 		nullptr, //SwsFilter* src_filter
 		nullptr, //SwsFilter* dst_filter
@@ -102,7 +122,7 @@ void Decoder::init_sws_context() {
 		m_frame2->data,
 		m_frame2->linesize,
 		m_frame2_mem.get(),
-		static_cast<::AVPixelFormat>(FavouriteFormat),
+		m_dst_format,
 		m_context->width,
 		m_context->height,
 		Align

src/ffmpeg/decoder.hpp

@@ -3,6 +3,9 @@
 #include "avdeleter.hpp"
 #include <cstddef>
 #include <cstdint>
+extern "C" {
+#include <libavutil/pixfmt.h>
+} //extern C
 
 namespace mgs::ffmpeg {
 class Decoder {
@@ -13,11 +16,10 @@ public:
 	typedef unique_av_ptr<struct ::SwsContext> UniqueSwsContext;
 	typedef unique_av_ptr<std::uint8_t> UniqueAVMem;
 
-	static const int FavouriteFormat;
+	Decoder (UniqueAVCodecContext&& context, ::AVPixelFormat dst_format);
-
-	Decoder (UniqueAVCodecContext&& context);
 	~Decoder() noexcept;
 	std::size_t decode (const std::uint8_t* input, std::size_t input_size, std::uint8_t* out, std::size_t out_size);
+	::AVPixelFormat destination_format() const noexcept;
 
 private:
 	void init_sws_context();
@@ -28,5 +30,6 @@ private:
 	UniqueAVFrame m_frame1;
 	UniqueAVFrame m_frame2;
 	UniqueSwsContext m_sws_context;
+	::AVPixelFormat m_dst_format;
 };
 } //namespace mgs::ffmpeg

src/main.cpp

@@ -48,7 +48,7 @@ int main() {
 
 		mgs::ffmpeg::AVCodec avcodec{::AVCodecID::AV_CODEC_ID_MJPEG};
 		auto cam_frame_format = cam.frame_size();
-		auto decoder{avcodec.make_decoder(cam_frame_format.width, cam_frame_format.height)};
+		auto decoder{avcodec.make_decoder(cam_frame_format.width, cam_frame_format.height, ::AVPixelFormat::AV_PIX_FMT_RGB24)};
 
 		print_supported_frame_formats(cam);
 		cam.start_streaming();