From 492563c6e7376ed3c674ce32558458162e687ca7 Mon Sep 17 00:00:00 2001
From: Hans-Kristian Arntzen <post@themaister.net>
Date: Sun, 5 Nov 2023 00:32:14 +0100
Subject: [PATCH] Make audio rate control a bit more aggressive.

---
 video/ffmpeg_decode.cpp | 43 +++++++++++++++--------------------------
 1 file changed, 16 insertions(+), 27 deletions(-)

diff --git a/video/ffmpeg_decode.cpp b/video/ffmpeg_decode.cpp
index 2b55ea1d..186df966 100644
--- a/video/ffmpeg_decode.cpp
+++ b/video/ffmpeg_decode.cpp
@@ -535,6 +535,7 @@ struct VideoDecoder::Impl
 	double get_estimated_audio_playback_timestamp(double elapsed_time);
 	double latch_estimated_video_playback_timestamp(double elapsed_time, double target_latency);
 	void latch_estimated_audio_playback_timestamp(double pts);
+	void set_audio_delta_rate_factor(float delta);
 	double get_audio_buffering_duration();
 	double get_last_video_buffering_pts();
 	unsigned get_num_ready_video_frames();
@@ -2197,20 +2198,14 @@ double VideoDecoder::Impl::get_audio_buffering_duration()
 #endif
 }
 
-void VideoDecoder::Impl::latch_estimated_audio_playback_timestamp(double pts)
+void VideoDecoder::Impl::set_audio_delta_rate_factor(float delta)
 {
-#ifdef HAVE_GRANITE_AUDIO
-	if (!stream)
-		return;
-
-	auto delta = float(pts - get_estimated_audio_playback_timestamp_raw());
-
-	if (delta > 0.25f)
+	if (delta > 0.10f)
 	{
 		// Speed up, audio buffer is too large.
 		stream->set_rate_factor(1.005f);
 	}
-	else if (delta < -0.25f)
+	else if (delta < -0.10f)
 	{
 		// Slow down.
 		stream->set_rate_factor(0.995f);
@@ -2219,8 +2214,18 @@ void VideoDecoder::Impl::latch_estimated_audio_playback_timestamp(double pts)
 	{
 		// This is inaudible in practice. Practical distortion will be much lower than outer limits.
 		// And should be less than 1 cent on average.
-		stream->set_rate_factor(1.0f + delta * 0.02f);
+		stream->set_rate_factor(1.0f + delta * 0.05f);
 	}
+}
+
+void VideoDecoder::Impl::latch_estimated_audio_playback_timestamp(double pts)
+{
+#ifdef HAVE_GRANITE_AUDIO
+	if (!stream)
+		return;
+
+	auto delta = float(pts - get_estimated_audio_playback_timestamp_raw());
+	set_audio_delta_rate_factor(delta);
 #else
 	(void)pts;
 #endif
@@ -2234,23 +2239,7 @@ void VideoDecoder::Impl::latch_audio_buffering_target(double target_buffer_time)
 
 	double current_time = get_audio_buffering_duration();
 	auto delta = float(current_time - target_buffer_time);
-
-	if (delta > 0.25f)
-	{
-		// Speed up, audio buffer is too large.
-		stream->set_rate_factor(1.005f);
-	}
-	else if (delta < -0.25f)
-	{
-		// Slow down.
-		stream->set_rate_factor(0.995f);
-	}
-	else
-	{
-		// This is inaudible in practice. Practical distortion will be much lower than outer limits.
-		// And should be less than 1 cent on average.
-		stream->set_rate_factor(1.0f + delta * 0.02f);
-	}
+	set_audio_delta_rate_factor(delta);
 #else
 	(void)target_buffer_time;
 #endif