From 5ff1f28af8dbbc3c030c612c8334a0702c7cae96 Mon Sep 17 00:00:00 2001
From: Mads Kiilerich <mads@kiilerich.com>
Date: Thu, 13 Oct 2022 17:25:53 +0200
Subject: [PATCH] Introduce internal MP3 support using libsndfile 1.1.0+

---
 libs/ardour/ardour/export_formats.h  | 26 +++++++++++++++++++
 libs/ardour/export_format_manager.cc |  5 ++++
 libs/ardour/export_formats.cc        | 38 ++++++++++++++++++++++++++++
 libs/ardour/export_graph_builder.cc  |  3 ++-
 libs/ardour/sndfile_helpers.cc       |  2 ++
 5 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/libs/ardour/ardour/export_formats.h b/libs/ardour/ardour/export_formats.h
index 04f35e5450..625e1646ea 100644
--- a/libs/ardour/ardour/export_formats.h
+++ b/libs/ardour/ardour/export_formats.h
@@ -355,6 +355,32 @@ public:
 	}
 };
 
+class LIBARDOUR_API ExportFormatMPEG : public ExportFormat, public HasSampleFormat, public HasCodecQuality
+{
+public:
+	ExportFormatMPEG (std::string const& name, std::string const& ext);
+	~ExportFormatMPEG (){};
+
+	bool set_compatibility_state (ExportFormatCompatibility const& compatibility);
+
+	Type get_type () const
+	{
+		return T_Sndfile;
+	}
+	SampleFormat default_sample_format () const
+	{
+		return SF_MPEG_LAYER_III;
+	}
+	int default_codec_quality () const
+	{
+		return 40;
+	}
+	virtual bool supports_tagging () const
+	{
+		return true;
+	}
+};
+
 class LIBARDOUR_API ExportFormatFFMPEG : public ExportFormat, public HasCodecQuality
 {
 public:
diff --git a/libs/ardour/export_format_manager.cc b/libs/ardour/export_format_manager.cc
index 14db27fbf8..3ddde3ad78 100644
--- a/libs/ardour/export_format_manager.cc
+++ b/libs/ardour/export_format_manager.cc
@@ -218,6 +218,11 @@ ExportFormatManager::init_formats ()
 	if (ArdourVideoToolPaths::transcoder_exe (unused, unused)) {
 		f_ptr.reset (new ExportFormatFFMPEG ("MP3", "mp3"));
 		add_format (f_ptr);
+	} else {
+		try {
+			f_ptr.reset (new ExportFormatMPEG ("MP3", "mp3"));
+			add_format (f_ptr);
+		} catch (ExportFormatIncompatible & e) {}
 	}
 }
 
diff --git a/libs/ardour/export_formats.cc b/libs/ardour/export_formats.cc
index 6b6fe09e86..b6cbad0c3a 100644
--- a/libs/ardour/export_formats.cc
+++ b/libs/ardour/export_formats.cc
@@ -382,6 +382,44 @@ ExportFormatBWF::set_compatibility_state (ExportFormatCompatibility const & comp
 }
 
 
+/*** MPEG / MP3 ***/
+
+ExportFormatMPEG::ExportFormatMPEG (std::string const& name, std::string const& ext) :
+  HasSampleFormat (sample_formats)
+{
+	SF_INFO sf_info;
+	sf_info.channels = 2;
+	sf_info.samplerate = SR_44_1;
+	sf_info.format = F_MPEG | SF_MPEG_LAYER_III;
+	if (sf_format_check (&sf_info) != SF_TRUE) {
+		throw ExportFormatIncompatible();
+	}
+
+	set_name (name);
+	set_format_id (F_MPEG);
+	add_sample_format (SF_MPEG_LAYER_III);
+
+	add_endianness (E_FileDefault);
+
+	// libsndfile doesn't expose direct quality control - use these coarse approximations
+	add_codec_quality ("Low (0%)",            0);
+	add_codec_quality ("Default (40%)",      40);
+	add_codec_quality ("High (60%)",         60);
+	add_codec_quality ("Very High (100%)",  100);
+
+	set_extension (ext);
+	set_quality (Q_LossyCompression);
+}
+
+bool
+ExportFormatMPEG::set_compatibility_state (ExportFormatCompatibility const & compatibility)
+{
+	bool compatible = compatibility.has_format (F_MPEG);
+	set_compatible (compatible);
+	return compatible;
+}
+
+
 /*** FFMPEG Pipe ***/
 
 ExportFormatFFMPEG::ExportFormatFFMPEG (std::string const& name, std::string const& ext)
diff --git a/libs/ardour/export_graph_builder.cc b/libs/ardour/export_graph_builder.cc
index 0a785283d0..a25fd39734 100644
--- a/libs/ardour/export_graph_builder.cc
+++ b/libs/ardour/export_graph_builder.cc
@@ -344,7 +344,8 @@ ExportGraphBuilder::Encoder::init_writer (boost::shared_ptr<AudioGrapher::Sndfil
 
 	writer.reset (new AudioGrapher::SndfileWriter<T> (writer_filename, format, channels, config.format->sample_rate(), config.broadcast_info));
 	writer->FileWritten.connect_same_thread (copy_files_connection, boost::bind (&ExportGraphBuilder::Encoder::copy_files, this, _1));
-	if ((format & SF_FORMAT_SUBMASK) == ExportFormatBase::SF_Vorbis) {
+	if ((format & SF_FORMAT_SUBMASK) == ExportFormatBase::SF_Vorbis ||
+	    (format & SF_FORMAT_TYPEMASK) == ExportFormatBase::F_MPEG) {
 		/* libsndfile uses range 0..1 (worst.. best) for
 		 * SFC_SET_VBR_ENCODING_QUALITY and maps
 		 * SFC_SET_COMPRESSION_LEVEL = 1.0 - VBR_ENCODING_QUALITY
diff --git a/libs/ardour/sndfile_helpers.cc b/libs/ardour/sndfile_helpers.cc
index 0261fa76a4..372036fdc6 100644
--- a/libs/ardour/sndfile_helpers.cc
+++ b/libs/ardour/sndfile_helpers.cc
@@ -21,6 +21,7 @@
 #include <strings.h>
 #include <sndfile.h>
 #include "ardour/sndfile_helpers.h"
+#include "ardour/export_format_base.h"
 
 using namespace std;
 
@@ -41,6 +42,7 @@ sndfile_data_width (int format)
 		return 32;
 	case SF_FORMAT_FLOAT:
 	case SF_FORMAT_DOUBLE:
+	case ARDOUR::ExportFormatBase::SF_MPEG_LAYER_III:
 		return 1; /* ridiculous but used as a magic value */
 	default:
 		// we don't handle anything else within ardour