decoder/ffmpeg: add AVCodecContext wrapper class

src/decoder/plugins/FfmpegDecoderPlugin.cxx

@@ -29,6 +29,7 @@
 #include "lib/ffmpeg/Buffer.hxx"
 #include "lib/ffmpeg/Frame.hxx"
 #include "lib/ffmpeg/Format.hxx"
+#include "lib/ffmpeg/Codec.hxx"
 #include "../DecoderAPI.hxx"
 #include "FfmpegMetaData.hxx"
 #include "FfmpegIo.hxx"
@@ -524,23 +525,9 @@ FfmpegDecode(DecoderClient &client, InputStream &input,
 		return;
 	}
 
-	AVCodecContext *codec_context = avcodec_alloc_context3(codec);
-	if (codec_context == nullptr) {
-		LogError(ffmpeg_domain, "avcodec_alloc_context3() failed");
-		return;
-	}
-
-	AtScopeExit(&codec_context) {
-		avcodec_free_context(&codec_context);
-	};
-
-	avcodec_parameters_to_context(codec_context, av_stream.codecpar);
-
-	const int open_result = avcodec_open2(codec_context, codec, nullptr);
-	if (open_result < 0) {
-		LogError(ffmpeg_domain, "Could not open codec");
-		return;
-	}
+	Ffmpeg::CodecContext codec_context(*codec);
+	codec_context.FillFromParameters(*av_stream.codecpar);
+	codec_context.Open(*codec, nullptr);
 
 	const SampleFormat sample_format =
 		ffmpeg_sample_format(codec_context->sample_fmt);
@@ -583,7 +570,7 @@ FfmpegDecode(DecoderClient &client, InputStream &input,
 					  AVSEEK_FLAG_ANY|AVSEEK_FLAG_BACKWARD) < 0)
 				client.SeekError();
 			else {
-				avcodec_flush_buffers(codec_context);
+				codec_context.FlushBuffers();
 				min_frame = client.GetSeekFrame();
 				client.CommandFinished();
 			}

src/lib/ffmpeg/Codec.hxx

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2003-2019 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_FFMPEG_CODEC_HXX
+#define MPD_FFMPEG_CODEC_HXX
+
+#include "Error.hxx"
+
+extern "C" {
+#include <libavcodec/avcodec.h>
+}
+
+#include <new>
+
+namespace Ffmpeg {
+
+class CodecContext {
+	AVCodecContext *codec_context = nullptr;
+
+public:
+	CodecContext() = default;
+
+	explicit CodecContext(AVCodec &codec)
+		:codec_context(avcodec_alloc_context3(&codec))
+	{
+		if (codec_context == nullptr)
+			throw std::bad_alloc();
+	}
+
+	~CodecContext() noexcept {
+		if (codec_context != nullptr)
+			avcodec_free_context(&codec_context);
+	}
+
+	CodecContext(CodecContext &&src) noexcept
+		:codec_context(std::exchange(src.codec_context, nullptr)) {}
+
+	CodecContext &operator=(CodecContext &&src) noexcept {
+		using std::swap;
+		swap(codec_context, src.codec_context);
+		return *this;
+	}
+
+	AVCodecContext &operator*() noexcept {
+		return *codec_context;
+	}
+
+	AVCodecContext *operator->() noexcept {
+		return codec_context;
+	}
+
+	void FillFromParameters(const AVCodecParameters &par) {
+		int err = avcodec_parameters_to_context(codec_context, &par);
+		if (err < 0)
+			throw MakeFfmpegError(err, "avcodec_parameters_to_context() failed");
+	}
+
+	void Open(const AVCodec &codec, AVDictionary **options) {
+		int err = avcodec_open2(codec_context, &codec, options);
+		if (err < 0)
+			throw MakeFfmpegError(err, "avcodec_open2() failed");
+	}
+
+	void FlushBuffers() noexcept {
+		avcodec_flush_buffers(codec_context);
+	}
+};
+
+} // namespace Ffmpeg
+
+#endif