From ed88e41fc52567cc9dd3e04d66e75238130259f4 Mon Sep 17 00:00:00 2001
From: Marten Richter <marten.richter@freenet.de>
Date: Sat, 23 Nov 2013 13:56:25 +0100
Subject: [PATCH] Detect mpeg audio frame header changes, and wait at least 4
 packets after a change for audio output

---
 audioomx.cc | 24 +++++++++++++++++++++---
 audioomx.h  |  3 +++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/audioomx.cc b/audioomx.cc
index 09a66ea..4703bbf 100644
--- a/audioomx.cc
+++ b/audioomx.cc
@@ -64,6 +64,8 @@ AudioOMX::AudioOMX()
   decompress_buffer=NULL;
   decompress_buffer_size=0;
   decompress_buffer_filled=0;
+  mp3sameheader=0;
+  mp3sameheadercount=0;
 
 }
 
@@ -1579,6 +1581,9 @@ unsigned int AudioOMX::AdvanceMpAudioSync(const UCHAR *data,unsigned int size,un
 	//inspired by libav parsing code
 	while (test+1<size) {
 		if (data[test]==0xFF && (data[test+1] &0xe0)==0xe0) {
+			//sanity check inspired by libav
+
+
 			const int sample_rates[4]={44100,48000,32000,0};
 			const short bitrate_tab[2][3][15] = { { { 0, 32, 64, 96, 128, 160,
 					192, 224, 256, 288, 320, 352, 384, 416, 448 }, { 0, 32, 48,
@@ -1620,11 +1625,23 @@ unsigned int AudioOMX::AdvanceMpAudioSync(const UCHAR *data,unsigned int size,un
 				frame_size=(temp_frame_size*144000)/(sample_rate<<lsf);
 				frame_size=frame_size+padding;
 			}
+			unsigned int sameheadertest=(data[test]<<24)|(data[test+1]<<16) |(data[test+2]<<8);
+			const unsigned mask=(0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19)); // from libav
+			if (!mp3sameheader) {
+				mp3sameheader=sameheadertest;
+				mp3sameheadercount=2;
+			}
+			if ((mp3sameheader& mask)== (sameheadertest &mask)) mp3sameheadercount++;
+			else mp3sameheadercount=0;
+			mp3sameheader=sameheadertest;
+
 			//Log::getInstance()->log("Audio", Log::DEBUG, "FRAME: %d %d %d %d %d %d %d",lsf,layer,bitrate_index,sample_rate,padding,temp_frame_size, frame_size);
-			//Log::getInstance()->log("Audio", Log::DEBUG, "FRAME DIAG: %x %x %x ",data[test],data[test+1],data[test+2]);
-			*framesize=frame_size;
+			//Log::getInstance()->log("Audio", Log::DEBUG, "FRAME DIAG: %x %x %x %d",data[test],data[test+1],data[test+2],mp3sameheadercount);
 
-			return test; // probably FrameSync
+			if (mp3sameheadercount>4) {
+				*framesize=frame_size;
+				return test; // probably FrameSync
+			} //skip it if the header changes too frequently
 		}
 		test++;
 	}
@@ -1829,6 +1846,7 @@ UINT AudioOMX::DeliverMediaPacket(MediaPacket packet, const UCHAR* buffer,
 	if (packet.type != lastAType) {//Format Change //Push data out !
 		firstsynched = false;
 		achange=true;
+		mp3sameheader=0;
 		Log::getInstance()->log("Audio", Log::DEBUG,"Notice audio type change %d %d", packet.type,lastAType);
 		lastAType = packet.type;
 		decompress_buffer_filled=0;
diff --git a/audioomx.h b/audioomx.h
index 42f525b..b6b01e0 100644
--- a/audioomx.h
+++ b/audioomx.h
@@ -198,6 +198,9 @@ class AudioOMX : public Audio
     unsigned int decompress_buffer_filled;
     bool lsync;
 
+    unsigned int mp3sameheader;
+    int mp3sameheadercount;
+
 
 	 int InitDecoderLibAV();
 	 void DeinitDecoderLibAV();
-- 
2.39.5