decoder/ffmpeg: add AVFormatContext wrapper class

src/decoder/plugins/FfmpegDecoderPlugin.cxx

@@ -28,6 +28,7 @@
 #include "lib/ffmpeg/Init.hxx"
 #include "lib/ffmpeg/Buffer.hxx"
 #include "lib/ffmpeg/Frame.hxx"
+#include "lib/ffmpeg/Format.hxx"
 #include "../DecoderAPI.hxx"
 #include "FfmpegMetaData.hxx"
 #include "FfmpegIo.hxx"
@@ -58,24 +59,18 @@ extern "C" {
  */
 static AVDictionary *avformat_options = nullptr;
 
-static AVFormatContext *
+static Ffmpeg::FormatContext
 FfmpegOpenInput(AVIOContext *pb,
 		const char *filename,
 		AVInputFormat *fmt)
 {
-	AVFormatContext *context = avformat_alloc_context();
-	if (context == nullptr)
-		throw std::runtime_error("avformat_alloc_context() failed");
-
-	context->pb = pb;
+	Ffmpeg::FormatContext context(pb);
 
 	AVDictionary *options = nullptr;
 	AtScopeExit(&options) { av_dict_free(&options); };
 	av_dict_copy(&options, avformat_options, 0);
 
-	int err = avformat_open_input(&context, filename, fmt, &options);
-	if (err < 0)
-		throw MakeFfmpegError(err, "avformat_open_input() failed");
+	context.OpenInput(filename, fmt, &options);
 
 	return context;
 }
@@ -628,13 +623,9 @@ ffmpeg_decode(DecoderClient &client, InputStream &input)
 		return;
 	}
 
-	AVFormatContext *format_context =
+	auto format_context =
 		FfmpegOpenInput(stream.io, input.GetURI(), nullptr);
 
-	AtScopeExit(&format_context) {
-		avformat_close_input(&format_context);
-	};
-
 	const auto *input_format = format_context->iformat;
 	FormatDebug(ffmpeg_domain, "detected input format '%s' (%s)",
 		    input_format->name, input_format->long_name);
@@ -683,11 +674,7 @@ try {
 	if (!stream.Open())
 		return false;
 
-	AVFormatContext *f = FfmpegOpenInput(stream.io, is.GetURI(), nullptr);
-	AtScopeExit(&f) {
-		avformat_close_input(&f);
-	};
-
+	auto f = FfmpegOpenInput(stream.io, is.GetURI(), nullptr);
 	return FfmpegScanStream(*f, handler);
 } catch (...) {
 	return false;

src/lib/ffmpeg/Format.hxx

@@ -0,0 +1,81 @@
+/*
+ * 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_FORMAT_HXX
+#define MPD_FFMPEG_FORMAT_HXX
+
+#include "Error.hxx"
+
+extern "C" {
+#include <libavformat/avformat.h>
+}
+
+#include <new>
+
+namespace Ffmpeg {
+
+class FormatContext {
+	AVFormatContext *format_context = nullptr;
+
+public:
+	FormatContext() = default;
+
+	explicit FormatContext(AVIOContext *pb)
+		:format_context(avformat_alloc_context())
+	{
+		if (format_context == nullptr)
+			throw std::bad_alloc();
+
+		format_context->pb = pb;
+	}
+
+	~FormatContext() noexcept {
+		if (format_context != nullptr)
+			avformat_close_input(&format_context);
+	}
+
+	FormatContext(FormatContext &&src) noexcept
+		:format_context(std::exchange(src.format_context, nullptr)) {}
+
+	FormatContext &operator=(FormatContext &&src) noexcept {
+		using std::swap;
+		swap(format_context, src.format_context);
+		return *this;
+	}
+
+	void OpenInput(const char *url, AVInputFormat *fmt,
+		       AVDictionary **options) {
+		int err = avformat_open_input(&format_context, url, fmt,
+					      options);
+		if (err < 0)
+			throw MakeFfmpegError(err, "avformat_open_input() failed");
+	}
+
+	AVFormatContext &operator*() noexcept {
+		return *format_context;
+	}
+
+	AVFormatContext *operator->() noexcept {
+		return format_context;
+	}
+};
+
+} // namespace Ffmpeg
+
+#endif