dithering for the mpeg audio decoder

Originally committed as revision 3903 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 21 insertions, 0 deletions

diff --git a/libavcodec/mpegaudio.h b/libavcodec/mpegaudio.h
index e50e8bd6f6..072c41bda7 100644
--- a/libavcodec/mpegaudio.h
+++ b/libavcodec/mpegaudio.h
@@ -18,6 +18,10 @@
 #define MPA_DUAL    2
 #define MPA_MONO    3
 
+/* header + layer + bitrate + freq + lsf/mpeg25 */
+#define SAME_HEADER_MASK \
+   (0xffe00000 | (3 << 17) | (0xf << 12) | (3 << 10) | (3 << 19))
+
 int l2_select_table(int bitrate, int nb_channels, int freq, int lsf);
 int mpa_decode_header(AVCodecContext *avctx, uint32_t head);
 
@@ -29,3 +33,20 @@ extern const int sblimit_table[5];
 extern const int quant_steps[17];
 extern const int quant_bits[17];
 extern const int32_t mpa_enwindow[257];
+
+/* fast header check for resync */
+static inline int ff_mpa_check_header(uint32_t header){
+    /* header */
+    if ((header & 0xffe00000) != 0xffe00000)
+        return -1;
+    /* layer check */
+    if ((header & (3<<17)) == 0)
+        return -1;
+    /* bit rate */
+    if ((header & (0xf<<12)) == 0xf<<12)
+        return -1;
+    /* frequency */
+    if ((header & (3<<10)) == 3<<10)
+        return -1;
+    return 0;
+}