decoder/Bridge: truncate last chunk at the exact end_time

Instead of passing whole chunks to the MusicPipe and checking the
end_time after each chunk, truncate the last chunk if it would exceed
the end_time.  This requires keeping track of the absolute PCM frame
number.

This fixes a problem with gapless CUE song transitions: a small part
of the following song was always played twice.

Closes #113

2 files changed, 34 insertions, 7 deletions

diff --git a/src/decoder/Bridge.cxx b/src/decoder/Bridge.cxx
index 37fcb2bf9..73a396e23 100644
--- a/src/decoder/Bridge.cxx
+++ b/src/decoder/Bridge.cxx
@@ -300,6 +300,7 @@ DecoderBridge::CommandFinished()
 
 		initial_seek_running = false;
 		timestamp = dc.start_time.ToDoubleS();
+		absolute_frame = dc.start_time.ToScale<uint64_t>(dc.in_audio_format.sample_rate);
 		return;
 	}
 
@@ -319,6 +320,7 @@ DecoderBridge::CommandFinished()
 			convert->Reset();
 
 		timestamp = dc.seek_time.ToDoubleS();
+		absolute_frame = dc.seek_time.ToScale<uint64_t>(dc.in_audio_format.sample_rate);
 	}
 
 	dc.command = DecoderCommand::NONE;
@@ -427,6 +429,7 @@ DecoderBridge::SubmitTimestamp(double t)
 	assert(t >= 0);
 
 	timestamp = t;
+	absolute_frame = uint64_t(t * dc.in_audio_format.sample_rate);
 }
 
 DecoderCommand
@@ -464,6 +467,29 @@ DecoderBridge::SubmitData(InputStream *is,
 			return cmd;
 	}
 
+	cmd = DecoderCommand::NONE;
+
+	const size_t frame_size = dc.in_audio_format.GetFrameSize();
+	size_t data_frames = length / frame_size;
+
+	if (dc.end_time.IsPositive()) {
+		/* enforce the given end time */
+
+		const uint64_t end_frame =
+			dc.end_time.ToScale<uint64_t>(dc.in_audio_format.sample_rate);
+		if (absolute_frame >= end_frame)
+			return DecoderCommand::STOP;
+
+		const uint64_t remaining_frames = end_frame - absolute_frame;
+		if (data_frames >= remaining_frames) {
+			/* past the end of the range: truncate this
+			   data submission and stop the decoder */
+			data_frames = remaining_frames;
+			length = data_frames * frame_size;
+			cmd = DecoderCommand::STOP;
+		}
+	}
+
 	if (convert != nullptr) {
 		assert(dc.in_audio_format != dc.out_audio_format);
 
@@ -521,15 +547,11 @@ DecoderBridge::SubmitData(InputStream *is,
 
 		timestamp += (double)nbytes /
 			dc.out_audio_format.GetTimeToSize();
-
-		if (dc.end_time.IsPositive() &&
-		    timestamp >= dc.end_time.ToDoubleS())
-			/* the end of this range has been reached:
-			   stop decoding */
-			return DecoderCommand::STOP;
 	}
 
-	return DecoderCommand::NONE;
+	absolute_frame += data_frames;
+
+	return cmd;
 }
 
 DecoderCommand
diff --git a/src/decoder/Bridge.hxx b/src/decoder/Bridge.hxx
index 3b354c063..c34c95941 100644
--- a/src/decoder/Bridge.hxx
+++ b/src/decoder/Bridge.hxx
@@ -50,6 +50,11 @@ public:
 	double timestamp = 0;
 
 	/**
+	 * The time stamp of the next data chunk, in PCM frames.
+	 */
+	uint64_t absolute_frame = 0;
+
+	/**
 	 * Is the initial seek (to the start position of the sub-song)
 	 * pending, or has it been performed already?
 	 */