decoder/ffmpeg: add libfmt formatter for AVSampleFormat

NEWS

 ver 0.23.10 (not yet released)
+* decoder
+  - ffmpeg: fix libfmt 9 compiler warning
 * encoder
   - flac: fix failure when libFLAC is built without Ogg support
 * Windows

src/decoder/plugins/FfmpegDecoderPlugin.cxx

@@ -31,6 +31,7 @@
 #include "lib/ffmpeg/Format.hxx"
 #include "lib/ffmpeg/Codec.hxx"
 #include "lib/ffmpeg/SampleFormat.hxx"
+#include "lib/ffmpeg/LibFmt.hxx"
 #include "../DecoderAPI.hxx"
 #include "FfmpegMetaData.hxx"
 #include "FfmpegIo.hxx"

src/lib/ffmpeg/LibFmt.hxx

+/*
+ * Copyright 2003-2022 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.
+ */
+
+#pragma once
+
+extern "C" {
+#include <libavutil/samplefmt.h>
+}
+
+#include <fmt/format.h>
+
+template<>
+struct fmt::formatter<AVSampleFormat> : formatter<string_view>
+{
+	template<typename FormatContext>
+	auto format(const AVSampleFormat format, FormatContext &ctx) {
+		const char *name = av_get_sample_fmt_name(format);
+		if (name == nullptr)
+			name = "?";
+
+		return formatter<string_view>::format(name, ctx);
+	}
+};