From 961b570ff897b54beabdcb4c54e59049203ce10a Mon Sep 17 00:00:00 2001
From: Christian Gmeiner <christian.gmeiner@gmail.com>
Date: Mon, 7 Dec 2009 16:53:59 +0100
Subject: fixed bug #169 ffmpep warns that the frame size is incorrect. To fix
 this warning, we calcuate the frame size based on the mpeg audio header. This
 calculated value is used for avcodec_decode_audio functions.

---
 dxr3audiodecoder.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 6 deletions(-)

(limited to 'dxr3audiodecoder.c')

diff --git a/dxr3audiodecoder.c b/dxr3audiodecoder.c
index d65689c..b909485 100644
--- a/dxr3audiodecoder.c
+++ b/dxr3audiodecoder.c
@@ -101,13 +101,16 @@ void cDxr3AudioDecoder::Decode(cDxr3PesFrame *frame, uint32_t pts, cDxr3SyncBuff
         if ((buf[2] & 0xf0) != (lastBitrate & 0xf0)) {
             dsyslog("[dxr3-audiodecoder] found new audio header");
 
+            // recalculate used framesize
+            frameSize = calcFrameSize(buf);
+            dsyslog("[dxr3-audiodecoder] calculated frame size %d", frameSize);
+
             // we need now to reinit the deocder and to store the new
             // part from the audio header
             Init();
             lastBitrate = buf[2];
         }
     }
-
 #if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(52, 26, 0)
     uint8_t *ptr = const_cast<uint8_t *>(buf);
 
@@ -115,9 +118,9 @@ void cDxr3AudioDecoder::Decode(cDxr3PesFrame *frame, uint32_t pts, cDxr3SyncBuff
          out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
 
 #if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(51, 29, 0)
-        len = avcodec_decode_audio(contextAudio, (short *)(&pcmbuf), &out_size, ptr, length);
+        len = avcodec_decode_audio(contextAudio, (short *)(&pcmbuf), &out_size, ptr, frameSize);
 #else
-        len = avcodec_decode_audio2(contextAudio, (short *)(&pcmbuf), &out_size, ptr, length);
+        len = avcodec_decode_audio2(contextAudio, (short *)(&pcmbuf), &out_size, ptr, frameSize);
 #endif
 
         if (len < 0) {
@@ -139,9 +142,9 @@ void cDxr3AudioDecoder::Decode(cDxr3PesFrame *frame, uint32_t pts, cDxr3SyncBuff
     }
 #else
     avpkt.data = const_cast<uint8_t *>(buf);
-    avpkt.size = length;
+    avpkt.size = frameSize;
 
-    while (avpkt.size > 0) {
+    while (length > 0) {
         out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
 
         len = avcodec_decode_audio3(contextAudio, (short *)(&pcmbuf), &out_size, &avpkt);
@@ -160,7 +163,7 @@ void cDxr3AudioDecoder::Decode(cDxr3PesFrame *frame, uint32_t pts, cDxr3SyncBuff
             }
         }
 
-        avpkt.size -= len;
+        length -= len;
         avpkt.data += len;
     }
 #endif
@@ -288,6 +291,69 @@ bool cDxr3AudioDecoder::checkMpegAudioHdr(const uint8_t *head)
     return true;
 }
 
+int cDxr3AudioDecoder::calcFrameSize(const uint8_t *header)
+{
+    static const int bitrates[2][3][15] =
+    {
+        {   // MPEG 1
+            {0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,},	// Layer1
+            {0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384,},	// Layer2
+            {0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320,}	// Layer3
+        },
+        {   // MPEG 2, 2.5
+            {0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,},     // Layer1
+            {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,},          // Layer2
+            {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,}           // Layer3
+        }
+    };
+
+    static const int samplingRates[4][3] =
+    {
+        {11025, 12000, 8000,  },    // MPEG 2.5
+        {0,     0,     0,     },    // reserved
+        {22050, 24000, 16000, },    // MPEG 2
+        {44100, 48000, 32000  }     // MPEG 1
+    };
+
+    static const int MPEG1 = 0x3;
+
+    // in B the version is stored
+    int ver = (header[1] >> 3) & 0x03;
+    int version = 1;    // default to MPEG2
+
+    // determine index into arrays based on ver
+    if (ver == MPEG1) {
+        version = 0;
+    }
+
+    // in C the layer version is stored
+    int layer = 3 - ((header[1] >> 1) & 0x03);
+
+    // in E the bitrate index is stored
+    int bitrateIndex = (header[2] >> 4) & 0x0f;
+
+    // in F the sampling rate frequency index is stored
+    int samplingIndex = (header[2] >> 2) & 0x03;
+
+    // in G the padding bit is stored
+    int padding = (header[2] >> 1) & 0x01;
+
+    int bitrate = bitrates[version][layer][bitrateIndex]; // kbit
+    bitrate *= 1000; // kbit -> bit
+    int samplesrate = samplingRates[ver][samplingIndex];
+
+    // formulars used to calculate frame size
+    //  layer I
+    //      FrameLengthInBytes = (12 * BitRate / SampleRate + Padding) * 4
+    //  layer II & III
+    //      FrameLengthInBytes = 144 * BitRate / SampleRate + Padding
+    if (layer == 0) {
+        return (12 * bitrate / samplesrate + padding) * 4;
+    } else {
+        return 144 * bitrate / samplesrate + padding;
+    }
+}
+
 // Local variables:
 // mode: c++
 // c-file-style: "stroustrup"
-- 
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