write iTunes compatible "Encoding Params" tag

main.cpp

@@ -1339,6 +1339,35 @@ bool insert_pce(uint32_t channel_layout, std::vector<uint8_t> *asc)
     return true;
 }
 
+static
+void set_encoding_params(AudioConverterX &converter, ITagStore *store)
+{
+    UInt32 mode = converter.getBitRateControlMode();
+    UInt32 bitrate = converter.getEncodeBitRate();
+    AudioStreamBasicDescription asbd;
+    converter.getOutputStreamDescription(&asbd);
+    UInt32 codec = asbd.mFormatID;
+    AudioComponentDescription cd = { 'aenc', codec, 'appl', 0, 0 };
+    auto ac = AudioComponentFindNext(nullptr, &cd);
+    UInt32 vers = 0;
+    AudioComponentGetVersion(ac, &vers);
+
+    char buf[32] = "vers\0\0\0\1acbf\0\0\0\0brat\0\0\0\0cdcv\0\0\0";
+    buf[12] = mode >> 24;
+    buf[13] = mode >> 16;
+    buf[14] = mode >> 8;
+    buf[15] = mode;
+    buf[20] = bitrate >> 24;
+    buf[21] = bitrate >> 16;
+    buf[22] = bitrate >> 8;
+    buf[23] = bitrate;
+    buf[28] = vers >> 24;
+    buf[29] = vers >> 16;
+    buf[30] = vers >> 8;
+    buf[31] = vers;
+    store->setTag("Encoding Params", std::string(buf, buf + 32));
+}
+
 static
 void encode_file(const std::shared_ptr<ISeekableSource> &src,
                  const std::wstring &ofilename, const Options &opts,
@@ -1388,6 +1417,11 @@ void encode_file(const std::shared_ptr<ISeekableSource> &src,
         sink = open_sink(ofilename, opts, oasbd,
                          channel_layout, cookie);
     encoder->setSink(sink);
+    if (opts.isAAC()) {
+        MP4Sink *mp4sink = dynamic_cast<MP4Sink*>(sink.get());
+        if (mp4sink)
+            set_encoding_params(converter, mp4sink);
+    }
     set_tags(src.get(), sink.get(), opts, encoder_config);
     CAFSink *cafsink = dynamic_cast<CAFSink*>(sink.get());
     if (cafsink)

sink.cpp

@@ -331,8 +331,11 @@ void MP4SinkBase::writeShortTag(uint32_t fcc, const std::string &value)
 void MP4SinkBase::writeLongTag(const std::string &key, const std::string &value)
 {
     const uint8_t *v = reinterpret_cast<const uint8_t *>(value.c_str());
+    auto type = mp4v2::impl::itmf::BT_UTF8;
+    if (key == "Encoding Params")
+        type = mp4v2::impl::itmf::BT_IMPLICIT;
     m_mp4file.SetMetadataFreeForm(key.c_str(), "com.apple.iTunes",
-                                  v, value.size());
+                                  v, value.size(), type);
 }
 
 void MP4SinkBase::writeTrackTag(const char *fcc, const std::string &value)