From 32f60d07a3dc359d97873ca4f24d8400a5fc251f Mon Sep 17 00:00:00 2001
From: jp9000 <obs.jim@gmail.com>
Date: Wed, 22 Feb 2017 01:18:24 -0800
Subject: [PATCH] win-dshow: Add LGP timestamp fix

LGP devices are devices that induce anger in any sane developer because
they're prone to bad audio timestamps when using their decoded data
directly.  For that reason, add a hack that smooths the timestamps
within a large threshold to prevent audio skipping.
---
 plugins/win-dshow/ffmpeg-decode.c | 32 ++++++++++++++++++++++++++++++-
 plugins/win-dshow/ffmpeg-decode.h |  8 +++++++-
 plugins/win-dshow/win-dshow.cpp   | 11 ++++++++++-
 3 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/plugins/win-dshow/ffmpeg-decode.c b/plugins/win-dshow/ffmpeg-decode.c
index 622fc9f48..f8d7b6e44 100644
--- a/plugins/win-dshow/ffmpeg-decode.c
+++ b/plugins/win-dshow/ffmpeg-decode.c
@@ -16,6 +16,8 @@
 ******************************************************************************/
 
 #include "ffmpeg-decode.h"
+#include <util/util_uint128.h>
+#include <util/base.h>
 #include <obs-avc.h>
 
 int ffmpeg_decode_init(struct ffmpeg_decode *decode, enum AVCodecID id)
@@ -107,8 +109,33 @@ static inline void copy_data(struct ffmpeg_decode *decode, uint8_t *data,
 	memcpy(decode->packet_buffer, data, size);
 }
 
+static void do_idiotic_lgp_audio_packet_realignment(
+		struct ffmpeg_decode *decode, long long *ts)
+{
+	uint64_t new_ts = (uint64_t)*ts;
+	util_uint128_t u128;
+
+	if (!decode->lgp_started) {
+		decode->lgp_start_ts = new_ts;
+		decode->lgp_next_expected_ts = new_ts;
+		decode->lgp_started = true;
+	}
+
+	if (llabs(decode->lgp_next_expected_ts - new_ts) < 3000000ULL) {
+		*ts = (long long)decode->lgp_next_expected_ts;
+	} else {
+		decode->lgp_start_ts = new_ts;
+		decode->lgp_frames_since_start = 0;
+	}
+
+	decode->lgp_frames_since_start += (uint64_t)decode->frame->nb_samples;
+	u128 = util_mul64_64(decode->lgp_frames_since_start, 10000000ULL);
+	decode->lgp_next_expected_ts = decode->lgp_start_ts +
+		util_div128_32(u128, (uint32_t)decode->frame->sample_rate).low;
+}
+
 int ffmpeg_decode_audio(struct ffmpeg_decode *decode,
-		uint8_t *data, size_t size,
+		uint8_t *data, size_t size, long long *ts,
 		struct obs_source_audio *audio,
 		bool *got_output)
 {
@@ -148,6 +175,9 @@ int ffmpeg_decode_audio(struct ffmpeg_decode *decode,
 	if (audio->format == AUDIO_FORMAT_UNKNOWN)
 		return 0;
 
+	if (decode->fix_braindead_lgp_audio_packet_stupidity)
+		do_idiotic_lgp_audio_packet_realignment(decode, ts);
+
 	*got_output = true;
 	return len;
 }
diff --git a/plugins/win-dshow/ffmpeg-decode.h b/plugins/win-dshow/ffmpeg-decode.h
index aca1be52e..ba5d76262 100644
--- a/plugins/win-dshow/ffmpeg-decode.h
+++ b/plugins/win-dshow/ffmpeg-decode.h
@@ -44,13 +44,19 @@ struct ffmpeg_decode {
 
 	uint8_t        *packet_buffer;
 	size_t         packet_size;
+
+	uint64_t       lgp_start_ts;
+	uint64_t       lgp_frames_since_start;
+	uint64_t       lgp_next_expected_ts;
+	bool           lgp_started;
+	bool           fix_braindead_lgp_audio_packet_stupidity;
 };
 
 extern int ffmpeg_decode_init(struct ffmpeg_decode *decode, enum AVCodecID id);
 extern void ffmpeg_decode_free(struct ffmpeg_decode *decode);
 
 extern int ffmpeg_decode_audio(struct ffmpeg_decode *decode,
-		uint8_t *data, size_t size,
+		uint8_t *data, size_t size, long long *ts,
 		struct obs_source_audio *audio,
 		bool *got_output);
 
diff --git a/plugins/win-dshow/win-dshow.cpp b/plugins/win-dshow/win-dshow.cpp
index 344745de0..ee820d6de 100644
--- a/plugins/win-dshow/win-dshow.cpp
+++ b/plugins/win-dshow/win-dshow.cpp
@@ -116,6 +116,7 @@ public:
 	inline ~Decoder() {ffmpeg_decode_free(&decode);}
 
 	inline operator ffmpeg_decode*() {return &decode;}
+	inline ffmpeg_decode *operator->() {return &decode;}
 };
 
 class CriticalSection {
@@ -507,10 +508,18 @@ void DShowInput::OnEncodedAudioData(enum AVCodecID id,
 			blog(LOG_WARNING, "Could not initialize audio decoder");
 			return;
 		}
+
+		if (videoConfig.name.find(L"C875") != std::string::npos ||
+		    videoConfig.name.find(L"C835") != std::string::npos) {
+			audio_decoder->fix_braindead_lgp_audio_packet_stupidity
+				= true;
+			blog(LOG_INFO, "Oh great, an LGP was detected.  "
+					"How wonderful.  I'm just ecstatic.");
+		}
 	}
 
 	bool got_output;
-	int len = ffmpeg_decode_audio(audio_decoder, data, size,
+	int len = ffmpeg_decode_audio(audio_decoder, data, size, &ts,
 			&audio, &got_output);
 	if (len < 0) {
 		blog(LOG_WARNING, "Error decoding audio");