move AC-3 header parsing to ac3.c

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

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;
+}

libavcodec/ac3.h

@@ -45,6 +45,50 @@ typedef struct AC3BitAllocParameters {
     int cplfleak, cplsleak;
 } AC3BitAllocParameters;
 
+/**
+ * @struct AC3HeaderInfo
+ * Coded AC-3 header values up to the lfeon element, plus derived values.
+ */
+typedef struct {
+    /** @defgroup coded Coded elements
+     * @{
+     */
+    uint16_t sync_word;
+    uint16_t crc1;
+    uint8_t fscod;
+    uint8_t frmsizecod;
+    uint8_t bsid;
+    uint8_t bsmod;
+    uint8_t acmod;
+    uint8_t cmixlev;
+    uint8_t surmixlev;
+    uint8_t dsurmod;
+    uint8_t lfeon;
+    /** @} */
+
+    /** @defgroup derived Derived values
+     * @{
+     */
+    uint8_t halfratecod;
+    uint16_t sample_rate;
+    uint32_t bit_rate;
+    uint8_t channels;
+    uint16_t frame_size;
+    /** @} */
+} AC3HeaderInfo;
+
+/**
+ * Parses AC-3 frame header.
+ * Parses the header up to the lfeon element, which is the first 52 or 54 bits
+ * depending on the audio coding mode.
+ * @param buf[in] Array containing the first 7 bytes of the frame.
+ * @param hdr[out] Pointer to struct where header info is written.
+ * @return Returns 0 on success, -1 if there is a sync word mismatch,
+ * -2 if the bsid (version) element is invalid, -3 if the fscod (sample rate)
+ * element is invalid, or -4 if the frmsizecod (bit rate) element is invalid.
+ */
+int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr);
+
 extern uint16_t ff_ac3_frame_sizes[38][3];
 extern const uint8_t ff_ac3_channels[8];
 extern const uint16_t ff_ac3_freqs[3];

libavcodec/parser.c

@@ -604,43 +604,26 @@ static const int aac_channels[8] = {
 static int ac3_sync(const uint8_t *buf, int *channels, int *sample_rate,
                     int *bit_rate, int *samples)
 {
-    unsigned int fscod, frmsizecod, acmod, bsid, lfeon, halfratecod;
+    int err;
+    unsigned int fscod, acmod, bsid, lfeon;
     unsigned int strmtyp, substreamid, frmsiz, fscod2, numblkscod;
     GetBitContext bits;
+    AC3HeaderInfo hdr;
 
-    init_get_bits(&bits, buf, AC3_HEADER_SIZE * 8);
+    err = ff_ac3_parse_header(buf, &hdr);
 
-    if(get_bits(&bits, 16) != 0x0b77)
+    if(err < 0 && err != -2)
         return 0;
 
-    bsid = show_bits_long(&bits, 29) & 0x1f;
+    bsid = hdr.bsid;
     if(bsid <= 10) {             /* Normal AC-3 */
-        skip_bits(&bits, 16);       /* crc */
-        fscod = get_bits(&bits, 2);
-        frmsizecod = get_bits(&bits, 6);
-
-        if(fscod == 3 && frmsizecod > 37)
-            return 0;
-
-        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);
-
-        halfratecod = FFMAX(bsid, 8) - 8;
-        *sample_rate = ff_ac3_freqs[fscod] >> halfratecod;
-        *bit_rate = (ff_ac3_bitratetab[frmsizecod] * 1000) >> halfratecod;
-        *channels = ff_ac3_channels[acmod] + lfeon;
-        *samples = 6 * 256;
-
-        return ff_ac3_frame_sizes[frmsizecod][fscod] * 2;
+        *sample_rate = hdr.sample_rate;
+        *bit_rate = hdr.bit_rate;
+        *channels = hdr.channels;
+        *samples = AC3_FRAME_SIZE;
+        return hdr.frame_size;
     } else if (bsid > 10 && bsid <= 16) { /* Enhanced AC-3 */
+        init_get_bits(&bits, &buf[2], (AC3_HEADER_SIZE-2) * 8);
         strmtyp = get_bits(&bits, 2);
         substreamid = get_bits(&bits, 3);