move AC-3 header parsing to ac3.c

Originally committed as revision 8323 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 51 insertions, 0 deletions

diff --git a/libavcodec/ac3.c b/libavcodec/ac3.c
index a1c46c6d2e..47c49c0d05 100644
--- a/libavcodec/ac3.c
+++ b/libavcodec/ac3.c
@@ -27,6 +27,7 @@
 #include "avcodec.h"
 #include "ac3.h"
 #include "ac3tab.h"
+#include "bitstream.h"
 
 static inline int calc_lowcomp1(int a, int b0, int b1, int c)
 {
@@ -208,3 +209,53 @@ void ac3_common_init(void)
         ff_ac3_frame_sizes[i][2] = (  3*br      );
     }
 }
+
+int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr)
+{
+    GetBitContext gbc;
+
+    memset(hdr, 0, sizeof(*hdr));
+
+    init_get_bits(&gbc, buf, 54);
+
+    hdr->sync_word = get_bits(&gbc, 16);
+    if(hdr->sync_word != 0x0B77)
+        return -1;
+
+    /* read ahead to bsid to make sure this is AC-3, not E-AC-3 */
+    hdr->bsid = show_bits_long(&gbc, 29) & 0x1F;
+    if(hdr->bsid > 10)
+        return -2;
+
+    hdr->crc1 = get_bits(&gbc, 16);
+    hdr->fscod = get_bits(&gbc, 2);
+    if(hdr->fscod == 3)
+        return -3;
+
+    hdr->frmsizecod = get_bits(&gbc, 6);
+    if(hdr->frmsizecod > 37)
+        return -4;
+
+    skip_bits(&gbc, 5); // skip bsid, already got it
+
+    hdr->bsmod = get_bits(&gbc, 3);
+    hdr->acmod = get_bits(&gbc, 3);
+    if((hdr->acmod & 1) && hdr->acmod != 1) {
+        hdr->cmixlev = get_bits(&gbc, 2);
+    }
+    if(hdr->acmod & 4) {
+        hdr->surmixlev = get_bits(&gbc, 2);
+    }
+    if(hdr->acmod == 2) {
+        hdr->dsurmod = get_bits(&gbc, 2);
+    }
+    hdr->lfeon = get_bits1(&gbc);
+
+    hdr->halfratecod = FFMAX(hdr->bsid, 8) - 8;
+    hdr->sample_rate = ff_ac3_freqs[hdr->fscod] >> hdr->halfratecod;
+    hdr->bit_rate = (ff_ac3_bitratetab[hdr->frmsizecod>>1] * 1000) >> hdr->halfratecod;
+    hdr->channels = ff_ac3_channels[hdr->acmod] + hdr->lfeon;
+    hdr->frame_size = ff_ac3_frame_sizes[hdr->frmsizecod][hdr->fscod] * 2;
+
+    return 0;
+}