decoder/flac: move the SubmitData() call out of the callback

NEWS

 ver 0.20.18 (not yet released)
+* decoder
+  - flac: improve seeking precision
 * fix gapless CUE song transitions
 
 ver 0.20.17 (2018/02/11)

src/decoder/plugins/FlacCommon.cxx

@@ -24,7 +24,6 @@
 #include "config.h"
 #include "FlacCommon.hxx"
 #include "FlacMetadata.hxx"
-#include "util/ConstBuffer.hxx"
 #include "Log.hxx"
 
 #include <stdexcept>
@@ -143,25 +142,10 @@ FlacDecoder::OnWrite(const FLAC__Frame &frame,
 	if (!initialized && !OnFirstFrame(frame.header))
 		return FLAC__STREAM_DECODER_WRITE_STATUS_ABORT;
 
-	const auto data = pcm_import.Import(buf, frame.header.blocksize);
+	chunk = pcm_import.Import(buf, frame.header.blocksize);
 
-	unsigned bit_rate = nbytes * 8 * frame.header.sample_rate /
+	kbit_rate = nbytes * 8 * frame.header.sample_rate /
 		(1000 * frame.header.blocksize);
 
-	auto cmd = GetClient()->SubmitData(GetInputStream(),
-					   data.data, data.size,
-					   bit_rate);
-	switch (cmd) {
-	case DecoderCommand::NONE:
-	case DecoderCommand::START:
-		break;
-
-	case DecoderCommand::STOP:
-		return FLAC__STREAM_DECODER_WRITE_STATUS_ABORT;
-
-	case DecoderCommand::SEEK:
-		return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
-	}
-
 	return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
 }

src/decoder/plugins/FlacCommon.hxx

@@ -27,6 +27,7 @@
 #include "FlacInput.hxx"
 #include "FlacPcm.hxx"
 #include "../DecoderAPI.hxx"
+#include "util/ConstBuffer.hxx"
 
 #include <FLAC/stream_decoder.h>
 
@@ -41,6 +42,12 @@ struct FlacDecoder : public FlacInput {
 	 */
 	bool unsupported = false;
 
+	/**
+	 * The kbit_rate parameter for the next
+	 * DecoderBridge::SubmitData() call.
+	 */
+	uint16_t kbit_rate;
+
 	FlacPcmImport pcm_import;
 
 	/**
@@ -51,6 +58,13 @@ struct FlacDecoder : public FlacInput {
 
 	Tag tag;
 
+	/**
+	 * Decoded PCM data obtained by our libFLAC write callback.
+	 * If this is non-empty, then DecoderBridge::SubmitData()
+	 * should be called.
+	 */
+	ConstBuffer<void> chunk = nullptr;
+
 	FlacDecoder(DecoderClient &_client, InputStream &_input_stream)
 		:FlacInput(_input_stream, &_client) {}
 

src/decoder/plugins/FlacDecoderPlugin.cxx

@@ -142,13 +142,28 @@ flac_decoder_initialize(FlacDecoder *data, FLAC__StreamDecoder *sd)
 static DecoderCommand
 FlacSubmitToClient(DecoderClient &client, FlacDecoder &d) noexcept
 {
+	if (d.tag.IsEmpty() && d.chunk.IsEmpty())
+		return client.GetCommand();
+
 	if (!d.tag.IsEmpty()) {
 		auto cmd = client.SubmitTag(d.GetInputStream(),
 					    std::move(d.tag));
 		d.tag.Clear();
+		if (cmd != DecoderCommand::NONE)
 			return cmd;
-	} else
-		return client.GetCommand();
+	}
+
+	if (!d.chunk.IsEmpty()) {
+		auto cmd = client.SubmitData(d.GetInputStream(),
+					     d.chunk.data,
+					     d.chunk.size,
+					     d.kbit_rate);
+		d.chunk = nullptr;
+		if (cmd != DecoderCommand::NONE)
+			return cmd;
+	}
+
+	return DecoderCommand::NONE;
 }
 
 static void