libavcodec/ac3dec.c

   1 /*
   2  * AC3 decoder
   3  * Copyright (c) 2001 Fabrice Bellard.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18  */
  19
  20 /**
  21  * @file ac3dec.c
  22  * AC3 decoder.
  23  */
  24
  25 //#define DEBUG
  26
  27 #include "avcodec.h"
  28 #include "libac3/ac3.h"
  29
  30 /* currently, I use libac3 which is Copyright (C) Aaron Holtzman and
  31    released under the GPL license. I may reimplement it someday... */
  32 typedef struct AC3DecodeState {
  33     uint8_t inbuf[4096]; /* input buffer */
  34     uint8_t *inbuf_ptr;
  35     int frame_size;
  36     int flags;
  37     int channels;
  38     ac3_state_t state;
  39 } AC3DecodeState;
  40
  41 static int ac3_decode_init(AVCodecContext *avctx)
  42 {
  43     AC3DecodeState *s = avctx->priv_data;
  44
  45     ac3_init ();
  46     s->inbuf_ptr = s->inbuf;
  47     s->frame_size = 0;
  48     return 0;
  49 }
  50
  51 stream_samples_t samples;
  52
  53 /**** the following two functions comes from ac3dec */
  54 static inline int blah (int32_t i)
  55 {
  56     if (i > 0x43c07fff)
  57         return 32767;
  58     else if (i < 0x43bf8000)
  59         return -32768;
  60     else
  61         return i - 0x43c00000;
  62 }
  63
  64 static inline void float_to_int (float * _f, int16_t * s16, int nchannels)
  65 {
  66     int i, j, c;
  67     int32_t * f = (int32_t *) _f;       // XXX assumes IEEE float format
  68
  69     j = 0;
  70     nchannels *= 256;
  71     for (i = 0; i < 256; i++) {
  72         for (c = 0; c < nchannels; c += 256)
  73             s16[j++] = blah (f[i + c]);
  74     }
  75 }
  76
  77 /**** end */
  78
  79 #define HEADER_SIZE 7
  80
  81 static int ac3_decode_frame(AVCodecContext *avctx,
  82                             void *data, int *data_size,
  83                             uint8_t *buf, int buf_size)
  84 {
  85     AC3DecodeState *s = avctx->priv_data;
  86     uint8_t *buf_ptr;
  87     int flags, i, len;
  88     int sample_rate, bit_rate;
  89     short *out_samples = data;
  90     float level;
  91     static const int ac3_channels[8] = {
  92         2, 1, 2, 3, 3, 4, 4, 5
  93     };
  94
  95     buf_ptr = buf;
  96     while (buf_size > 0) {
  97         len = s->inbuf_ptr - s->inbuf;
  98         if (s->frame_size == 0) {
  99             /* no header seen : find one. We need at least 7 bytes to parse it */
 100             len = HEADER_SIZE - len;
 101             if (len > buf_size)
 102                 len = buf_size;
 103             memcpy(s->inbuf_ptr, buf_ptr, len);
 104             buf_ptr += len;
 105             s->inbuf_ptr += len;
 106             buf_size -= len;
 107             if ((s->inbuf_ptr - s->inbuf) == HEADER_SIZE) {
 108                 len = ac3_syncinfo (s->inbuf, &s->flags, &sample_rate, &bit_rate);
 109                 if (len == 0) {
 110                     /* no sync found : move by one byte (inefficient, but simple!) */
 111                     memcpy(s->inbuf, s->inbuf + 1, HEADER_SIZE - 1);
 112                     s->inbuf_ptr--;
 113                 } else {
 114                     s->frame_size = len;
 115                     /* update codec info */
 116                     avctx->sample_rate = sample_rate;
 117                     s->channels = ac3_channels[s->flags & 7];
 118                     if (s->flags & AC3_LFE)
 119                         s->channels++;
 120                     if (avctx->channels == 0)
 121                         /* No specific number of channel requested */
 122                         avctx->channels = s->channels;
 123                     else if (s->channels < avctx->channels) {
 124                         av_log( avctx, AV_LOG_INFO, "ac3dec: AC3 Source channels are less than specified: output to %d channels.. (frmsize: %d)\n", s->channels, len);
 125                         avctx->channels = s->channels;
 126                     }
 127                     avctx->bit_rate = bit_rate;
 128                 }
 129             }
 130         } else if (len < s->frame_size) {
 131             len = s->frame_size - len;
 132             if (len > buf_size)
 133                 len = buf_size;
 134
 135             memcpy(s->inbuf_ptr, buf_ptr, len);
 136             buf_ptr += len;
 137             s->inbuf_ptr += len;
 138             buf_size -= len;
 139         } else {
 140             flags = s->flags;
 141             if (avctx->channels == 1)
 142                 flags = AC3_MONO;
 143             else if (avctx->channels == 2)
 144                 flags = AC3_STEREO;
 145             else
 146                 flags |= AC3_ADJUST_LEVEL;
 147             level = 1;
 148             if (ac3_frame (&s->state, s->inbuf, &flags, &level, 384)) {
 149             fail:
 150                 s->inbuf_ptr = s->inbuf;
 151                 s->frame_size = 0;
 152                 continue;
 153             }
 154             for (i = 0; i < 6; i++) {
 155                 if (ac3_block (&s->state))
 156                     goto fail;
 157                 float_to_int (*samples, out_samples + i * 256 * avctx->channels, avctx->channels);
 158             }
 159             s->inbuf_ptr = s->inbuf;
 160             s->frame_size = 0;
 161             *data_size = 6 * avctx->channels * 256 * sizeof(int16_t);
 162             break;
 163         }
 164     }
 165     return buf_ptr - buf;
 166 }
 167
 168 static int ac3_decode_end(AVCodecContext *s)
 169 {
 170     return 0;
 171 }
 172
 173 AVCodec ac3_decoder = {
 174     "ac3",
 175     CODEC_TYPE_AUDIO,
 176     CODEC_ID_AC3,
 177     sizeof(AC3DecodeState),
 178     ac3_decode_init,
 179     NULL,
 180     ac3_decode_end,
 181     ac3_decode_frame,
 182 };