dithering for the mpeg audio decoder

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

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;
+}

libavcodec/mpegaudiodec.c

@@ -99,6 +99,7 @@ typedef struct MPADecodeContext {
 #endif
     void (*compute_antialias)(struct MPADecodeContext *s, struct GranuleDef *g);
     int adu_mode; ///< 0 for standard mp3, 1 for adu formatted mp3
+    unsigned int dither_state;
 } MPADecodeContext;
 
 /* layer 3 "granule" */
@@ -749,10 +750,11 @@ static void dct32(int32_t *out, int32_t *tab)
 
 #if FRAC_BITS <= 15
 
-static inline int round_sample(int sum)
+static inline int round_sample(int *sum)
 {
     int sum1;
-    sum1 = (sum + (1 << (OUT_SHIFT - 1))) >> OUT_SHIFT;
+    sum1 = (*sum) >> OUT_SHIFT;
+    *sum &= (1<<OUT_SHIFT)-1;
     if (sum1 < -32768)
         sum1 = -32768;
     else if (sum1 > 32767)
@@ -782,10 +784,11 @@ static inline int round_sample(int sum)
 
 #else
 
-static inline int round_sample(int64_t sum) 
+static inline int round_sample(int64_t *sum) 
 {
     int sum1;
-    sum1 = (int)((sum + (int64_t_C(1) << (OUT_SHIFT - 1))) >> OUT_SHIFT);
+    sum1 = (int)((*sum) >> OUT_SHIFT);
+    *sum &= (1<<OUT_SHIFT)-1;
     if (sum1 < -32768)
         sum1 = -32768;
     else if (sum1 > 32767)
@@ -900,37 +903,37 @@ void ff_mpa_synth_filter(MPA_INT *synth_buf_ptr, int *synth_buf_offset,
     w = window;
     w2 = window + 31;
 
-    sum = 0;
+    sum = s1->dither_state;
     p = synth_buf + 16;
     SUM8(sum, +=, w, p);
     p = synth_buf + 48;
     SUM8(sum, -=, w + 32, p);
-    *samples = round_sample(sum);
+    *samples = round_sample(&sum);
     samples += incr;
     w++;
 
     /* we calculate two samples at the same time to avoid one memory
        access per two sample */
     for(j=1;j<16;j++) {
-        sum = 0;
         sum2 = 0;
         p = synth_buf + 16 + j;
         SUM8P2(sum, +=, sum2, -=, w, w2, p);
         p = synth_buf + 48 - j;
         SUM8P2(sum, -=, sum2, -=, w + 32, w2 + 32, p);
 
-        *samples = round_sample(sum);
+        *samples = round_sample(&sum);
         samples += incr;
-        *samples2 = round_sample(sum2);
+        sum += sum2;
+        *samples2 = round_sample(&sum);
         samples2 -= incr;
         w++;
         w2--;
     }
     
     p = synth_buf + 32;
-    sum = 0;
     SUM8(sum, -=, w + 32, p);
-    *samples = round_sample(sum);
+    *samples = round_sample(&sum);
+    s1->dither_state= sum;
 
     offset = (offset - 32) & 511;
     *synth_buf_offset = offset;
@@ -1115,28 +1118,6 @@ static void imdct36(int *out, int *in)
     out[8 - 4] = t1;
 }
 
-/* fast header check for resync */
-static int check_header(uint32_t header)
-{
-    /* header */
-    if ((header & 0xffe00000) != 0xffe00000)
-	return -1;
-    /* layer check */
-    if (((header >> 17) & 3) == 0)
-	return -1;
-    /* bit rate */
-    if (((header >> 12) & 0xf) == 0xf)
-	return -1;
-    /* frequency */
-    if (((header >> 10) & 3) == 3)
-	return -1;
-    return 0;
-}
-
-/* header + layer + bitrate + freq + lsf/mpeg25 */
-#define SAME_HEADER_MASK \
-   (0xffe00000 | (3 << 17) | (0xf << 12) | (3 << 10) | (3 << 19))
-
 /* header decoding. MUST check the header before because no
    consistency check is done there. Return 1 if free format found and
    that the frame size must be computed externally */
@@ -1244,7 +1225,7 @@ int mpa_decode_header(AVCodecContext *avctx, uint32_t head)
     MPADecodeContext s1, *s = &s1;
     memset( s, 0, sizeof(MPADecodeContext) );
 
-    if (check_header(head) != 0)
+    if (ff_mpa_check_header(head) != 0)
         return -1;
 
     if (decode_header(s, head) != 0) {
@@ -2566,7 +2547,7 @@ static int decode_frame(AVCodecContext * avctx,
 		header = (s->inbuf[0] << 24) | (s->inbuf[1] << 16) |
 		    (s->inbuf[2] << 8) | s->inbuf[3];
 
-		if (check_header(header) < 0) {
+		if (ff_mpa_check_header(header) < 0) {
 		    /* no sync found : move by one byte (inefficient, but simple!) */
 		    memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
 		    s->inbuf_ptr--;
@@ -2712,7 +2693,7 @@ static int decode_frame_adu(AVCodecContext * avctx,
     header = (s->inbuf[0] << 24) | (s->inbuf[1] << 16) |
               (s->inbuf[2] << 8) | s->inbuf[3] | 0xffe00000;
 
-    if (check_header(header) < 0) { // Bad header, discard frame
+    if (ff_mpa_check_header(header) < 0) { // Bad header, discard frame
         *data_size = 0;
         return buf_size;
     }

tests/ffmpeg.regression.ref

@@ -125,8 +125,8 @@ ccc201054669e94717022bb4f2aea4ce *./data/out.yuv
 stddev: 10.99 PSNR:27.30 bytes:7602176
 21f8ff9f1daacd9133683bb4ea0f50a4 *./data/a-mp2.mp2
 95712 ./data/a-mp2.mp2
-91ab1b253cd360037d3fca67b795aba8 *./data/out.wav
+6956f2c5185c4edbae648c614992a14b *./data/out.wav
-stddev:117.02 PSNR: 6.75 bytes:1054720
+stddev:117.02 PSNR: 6.76 bytes:1054720
 d056da679e6d6682812fffb28a7f0db6 *./data/a-ac3.rm
 97983 ./data/a-ac3.rm
 2d081e0e1f2e9bd4514e9ac8ec41884c *./data/a-g726.wav

tests/libav.regression.ref

@@ -1,21 +1,21 @@
 ffmpeg regression test
 8517e7c83227074b8d632477fda310d5 *./data/b-libav.avi
 342282 ./data/b-libav.avi
-./data/b-libav.avi CRC=001a3415
+./data/b-libav.avi CRC=ccab3a27
 c83444a0e8ef47b6af1d868d1bb21696 *./data/b-libav.asf
 342967 ./data/b-libav.asf
-./data/b-libav.asf CRC=750f18c7
+./data/b-libav.asf CRC=41af1ed9
 5240a23a9264bc6062d6739c70825ace *./data/b-libav.rm
 360251 ./data/b-libav.rm
 90784a1b9589095f20fc6bcc0cc23cc4 *./data/b-libav.mpg
 387072 ./data/b-libav.mpg
-./data/b-libav.mpg CRC=16c74225
+./data/b-libav.mpg CRC=8b644837
 57a8dfc7926802bb337a9d8918de94a8 *./data/b-libav.swf
 41816 ./data/b-libav.swf
 ./data/b-libav.swf CRC=2b273fea
 2b06388316770915293edcbcc693beef *./data/b-libav.ffm
 389120 ./data/b-libav.ffm
-./data/b-libav.ffm CRC=f765cbdd
+./data/b-libav.ffm CRC=688bd1eb
 794934a02582f8dfc85d1856514cf37c *./data/b-libav.flv
 339325 ./data/b-libav.flv
 ./data/b-libav.flv CRC=7b9076f8
@@ -24,7 +24,7 @@ c83444a0e8ef47b6af1d868d1bb21696 *./data/b-libav.asf
 ./data/b-libav.mov CRC=da87a90d
 fea20ced22451312dd463110e594eda6 *./data/b-libav.nut
 332415 ./data/b-libav.nut
-./data/b-libav.nut CRC=001a3415
+./data/b-libav.nut CRC=ccab3a27
 29a2c312bbc5b187491183a918556475 *./data/b-libav.dv
 3600000 ./data/b-libav.dv
 ./data/b-libav.dv CRC=37b096b4

tests/rotozoom.regression.ref

@@ -125,8 +125,8 @@ stddev:  0.00 PSNR:99.99 bytes:7602176
 stddev:  3.43 PSNR:37.39 bytes:7602176
 21f8ff9f1daacd9133683bb4ea0f50a4 *./data/a-mp2.mp2
 95712 ./data/a-mp2.mp2
-91ab1b253cd360037d3fca67b795aba8 *./data/out.wav
+6956f2c5185c4edbae648c614992a14b *./data/out.wav
-stddev:117.02 PSNR: 6.75 bytes:1054720
+stddev:117.02 PSNR: 6.76 bytes:1054720
 d056da679e6d6682812fffb28a7f0db6 *./data/a-ac3.rm
 97983 ./data/a-ac3.rm
 2d081e0e1f2e9bd4514e9ac8ec41884c *./data/a-g726.wav