mp3文件解码- 哈夫曼码区1

哈夫曼码区边界

以下是MPEG官方文档Table 3-B.8a的表，哈夫曼编码时，576条频线分布情况
long blocks:

scale factor band（32k采样）	width of band	index of start	index of end
0	4	0	3
1	4	4	7
2	4	8	11
3	4	12	15
4	4	16	19
5	4	20	23
6	6	24	29
7	6	30	35
8	8	36	43
9	10	44	53
10	12	54	65
11	16	66	81
12	20	82	101
13	24	102	125
14	30	126	155
15	38	156	193
16	46	194	239
17	56	240	295
18	68	296	363
19	84	364	447
20	102	448	549

scale factor band（44.1k采样）	width of band	index of start	index of end
0	4	0	3
1	4	4	7
2	4	8	11
3	4	12	15
4	4	16	19
5	4	20	23
6	6	24	29
7	6	30	35
8	8	36	43
9	8	44	51
10	10	52	61
11	12	62	73
12	16	74	89
13	20	90	109
14	24	110	133
15	28	134	161
16	34	162	195
17	42	196	237
18	50	238	287
19	54	288	341
20	76	342	417

scale factor band（48k采样）	width of band	index of start	index of end
0	4	0	3
1	4	4	7
2	4	8	11
3	4	12	15
4	4	16	19
5	4	20	23
6	6	24	29
7	6	30	35
8	6	36	41
9	8	42	49
10	10	50	59
11	12	60	71
12	16	72	87
13	18	88	105
14	22	106	127
15	28	128	155
16	34	156	189
17	40	190	229
18	46	230	275
19	54	276	329
20	54	330	383

short blocks:

scale factor band（32k采样）	width of band	index of start	index of end
0	4	0	3
1	4	4	7
2	4	8	11
3	4	12	15
4	6	16	21
5	8	22	29
6	12	30	41
7	16	42	57
8	20	58	77
9	26	78	103
10	34	104	137
11	42	138	179

scale factor band（44.1k采样）	width of band	index of start	index of end
0	4	0	3
1	4	4	7
2	4	8	11
3	4	12	15
4	6	16	21
5	8	22	29
6	10	30	39
7	12	40	51
8	14	52	65
9	18	66	83
10	22	84	105
11	30	106	135

scale factor band（48k采样）	width of band	index of start	index of end
0	4	0	3
1	4	4	7
2	4	8	11
3	4	12	15
4	6	16	21
5	6	22	27
6	10	28	37
7	12	38	49
8	14	50	63
9	16	64	79
10	20	80	99
11	26	100	125

struct {
	int l[23];
	int s[14];
} sfBandIndex[3]= {
	{{0,4,8,12,16,20,24,30,36,44,52,62,74,90,110,134,162,196,238,288,342,418,576},
		{0,4,8,12,16,22,30,40,52,66,84,106,136,192}},
	{{0,4,8,12,16,20,24,30,36,42,50,60,72,88,106,128,156,190,230,276,330,384,576},
		{0,4,8,12,16,22,28,38,50,64,80,100,126,192}},
	{{0,4,8,12,16,20,24,30,36,44,54,66,82,102,126,156,194,240,296,364,448,550,576},
		{0,4,8,12,16,22,30,42,58,78,104,138,180,192}}
};

   /* Find region boundary for short block case. */

   if ( ((*si).ch[ch].gr[gr].window_switching_flag) &&
        ((*si).ch[ch].gr[gr].block_type == 2) ) {

      /* Region2. */

      region1Start = 36;  /* sfb[9/3]*3=36 */
      region2Start = 576; /* No Region2 for short block case. */
   }


   else {          /* Find region boundary for long block case. */

      region1Start = sfBandIndex[fr_ps->header->sampling_frequency]
                           .l[(*si).ch[ch].gr[gr].region0_count + 1]; /* MI */
      region2Start = sfBandIndex[fr_ps->header->sampling_frequency]
                              .l[(*si).ch[ch].gr[gr].region0_count +
                              (*si).ch[ch].gr[gr].region1_count + 2]; /* MI */
      }

这不确定是不是官方的，没有标记版权，ycb1698大佬的版本则包含了MPEG2 ，MPEG2.5的，在确定sync_word是11位还是12位的时候，找过不少资料，其中官方的文档主要是ISO_11172和ISO.IEC-13818-1，前一个文档的同步字是12bits，后一个文档并未提及2.5版本，后来有资料说这是个民间版本，卒。