[Ffmpeg-devel] [PATCH] Correctly parse headers of E-AC3 streams

[Ian Caulfield]

On 1/18/07, Michael Niedermayer <michaelni at gmx.at> wrote:
>
>
> ok, just resubmit the patch with the int->uint8_t and (fscod2 == 3) change
> and ill approve it


Done, here you go...

Ian
-------------- next part --------------
Index: libavcodec/parser.c
===================================================================
--- libavcodec/parser.c	(revision 7582)
+++ libavcodec/parser.c	(working copy)
@@ -632,9 +632,14 @@
     384, 448, 448, 512, 512, 576, 576, 640, 640,
 };
 
-static const int ac3_channels[8] = {
+static const uint8_t ac3_channels[8] = {
     2, 1, 2, 3, 3, 4, 4, 5
 };
+
+static const uint8_t eac3_blocks[4] = {
+    1, 2, 3, 6
+};
+
 #endif /* CONFIG_AC3_PARSER */
 
 #ifdef CONFIG_AAC_PARSER
@@ -653,6 +658,7 @@
                     int *bit_rate, int *samples)
 {
     unsigned int fscod, frmsizecod, acmod, bsid, lfeon;
+    unsigned int strmtyp, substreamid, frmsiz, fscod2, numblkscod;
     GetBitContext bits;
 
     init_get_bits(&bits, buf, AC3_HEADER_SIZE * 8);
@@ -660,32 +666,67 @@
     if(get_bits(&bits, 16) != 0x0b77)
         return 0;
 
-    skip_bits(&bits, 16);       /* crc */
-    fscod = get_bits(&bits, 2);
-    frmsizecod = get_bits(&bits, 6);
+    bsid = show_bits_long(&bits, 29) & 0x1f;
+    if(bsid <= 8) {             /* Normal AC-3 */
+        skip_bits(&bits, 16);       /* crc */
+        fscod = get_bits(&bits, 2);
+        frmsizecod = get_bits(&bits, 6);
 
-    if(!ac3_sample_rates[fscod])
-        return 0;
+        if(fscod == 3)
+            return 0;
 
-    bsid = get_bits(&bits, 5);
-    if(bsid > 8)
-        return 0;
-    skip_bits(&bits, 3);        /* bsmod */
-    acmod = get_bits(&bits, 3);
-    if(acmod & 1 && acmod != 1)
-        skip_bits(&bits, 2);    /* cmixlev */
-    if(acmod & 4)
-        skip_bits(&bits, 2);    /* surmixlev */
-    if(acmod & 2)
-        skip_bits(&bits, 2);    /* dsurmod */
-    lfeon = get_bits1(&bits);
+        skip_bits(&bits, 5);        /* bsid */
+        skip_bits(&bits, 3);        /* bsmod */
+        acmod = get_bits(&bits, 3);
+        if(acmod & 1 && acmod != 1)
+            skip_bits(&bits, 2);    /* cmixlev */
+        if(acmod & 4)
+            skip_bits(&bits, 2);    /* surmixlev */
+        if(acmod & 2)
+            skip_bits(&bits, 2);    /* dsurmod */
+        lfeon = get_bits1(&bits);
 
-    *sample_rate = ac3_sample_rates[fscod];
-    *bit_rate = ac3_bitrates[frmsizecod] * 1000;
-    *channels = ac3_channels[acmod] + lfeon;
-    *samples = 6 * 256;
+        *sample_rate = ac3_sample_rates[fscod];
+        *bit_rate = ac3_bitrates[frmsizecod] * 1000;
+        *channels = ac3_channels[acmod] + lfeon;
+        *samples = 6 * 256;
 
-    return ac3_frame_sizes[frmsizecod][fscod] * 2;
+        return ac3_frame_sizes[frmsizecod][fscod] * 2;
+    } else if (bsid >= 10 && bsid <= 16) { /* Enhanced AC-3 */
+        strmtyp = get_bits(&bits, 2);
+        substreamid = get_bits(&bits, 3);
+
+        if (strmtyp != 0 || substreamid != 0)
+            return 0;   /* Currently don't support additional streams */
+
+        frmsiz = get_bits(&bits, 11) + 1;
+        fscod = get_bits(&bits, 2);
+        if (fscod == 3) {
+            fscod2 = get_bits(&bits, 2);
+            numblkscod = 3;
+
+            if(fscod2i == 3)
+                return 0;
+
+            *sample_rate = ac3_sample_rates[fscod2] / 2;
+        } else {
+            numblkscod = get_bits(&bits, 2);
+
+            *sample_rate = ac3_sample_rates[fscod];
+        }
+
+        acmod = get_bits(&bits, 3);
+        lfeon = get_bits1(&bits);
+
+        *samples = eac3_blocks[numblkscod] * 256;
+        *bit_rate = frmsiz * (*sample_rate) * 16 / (*samples);
+        *channels = ac3_channels[acmod] + lfeon;
+
+        return frmsiz * 2;
+    }
+
+    /* Unsupported bitstream version */
+    return 0;
 }
 #endif /* CONFIG_AC3_PARSER */