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  1. /*
  2.  * copyright (c) 2008 Paul Kendall <paul@kcbbs.gen.nz>
  3.  *
  4.  * This file is part of FFmpeg.
  5.  *
  6.  * FFmpeg is free software; you can redistribute it and/or
  7.  * modify it under the terms of the GNU Lesser General Public
  8.  * License as published by the Free Software Foundation; either
  9.  * version 2.1 of the License, or (at your option) any later version.
  10.  *
  11.  * FFmpeg is distributed in the hope that it will be useful,
  12.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14.  * Lesser General Public License for more details.
  15.  *
  16.  * You should have received a copy of the GNU Lesser General Public
  17.  * License along with FFmpeg; if not, write to the Free Software
  18.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19.  */
  20.  
  21. /**
  22.  * @file
  23.  * AAC LATM parser
  24.  */
  25.  
  26. #include <stdint.h>
  27. #include "parser.h"
  28.  
  29. #define LATM_HEADER     0x56e000        // 0x2b7 (11 bits)
  30. #define LATM_MASK       0xFFE000        // top 11 bits
  31. #define LATM_SIZE_MASK  0x001FFF        // bottom 13 bits
  32.  
  33. typedef struct LATMParseContext{
  34.     ParseContext pc;
  35.     int count;
  36. } LATMParseContext;
  37.  
  38. /**
  39.  * Find the end of the current frame in the bitstream.
  40.  * @return the position of the first byte of the next frame, or -1
  41.  */
  42. static int latm_find_frame_end(AVCodecParserContext *s1, const uint8_t *buf,
  43.                                int buf_size)
  44. {
  45.     LATMParseContext *s = s1->priv_data;
  46.     ParseContext *pc    = &s->pc;
  47.     int pic_found, i;
  48.     uint32_t state;
  49.  
  50.     pic_found = pc->frame_start_found;
  51.     state     = pc->state;
  52.  
  53.     if (!pic_found) {
  54.         for (i = 0; i < buf_size; i++) {
  55.             state = (state<<8) | buf[i];
  56.             if ((state & LATM_MASK) == LATM_HEADER) {
  57.                 i++;
  58.                 s->count  = -i;
  59.                 pic_found = 1;
  60.                 break;
  61.             }
  62.         }
  63.     }
  64.  
  65.     if (pic_found) {
  66.         /* EOF considered as end of frame */
  67.         if (buf_size == 0)
  68.             return 0;
  69.         if ((state & LATM_SIZE_MASK) - s->count <= buf_size) {
  70.             pc->frame_start_found = 0;
  71.             pc->state             = -1;
  72.             return (state & LATM_SIZE_MASK) - s->count;
  73.         }
  74.     }
  75.  
  76.     s->count             += buf_size;
  77.     pc->frame_start_found = pic_found;
  78.     pc->state             = state;
  79.  
  80.     return END_NOT_FOUND;
  81. }
  82.  
  83. static int latm_parse(AVCodecParserContext *s1, AVCodecContext *avctx,
  84.                       const uint8_t **poutbuf, int *poutbuf_size,
  85.                       const uint8_t *buf, int buf_size)
  86. {
  87.     LATMParseContext *s = s1->priv_data;
  88.     ParseContext *pc    = &s->pc;
  89.     int next;
  90.  
  91.     if (s1->flags & PARSER_FLAG_COMPLETE_FRAMES) {
  92.         next = buf_size;
  93.     } else {
  94.         next = latm_find_frame_end(s1, buf, buf_size);
  95.  
  96.         if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
  97.             *poutbuf      = NULL;
  98.             *poutbuf_size = 0;
  99.             return buf_size;
  100.         }
  101.     }
  102.     *poutbuf      = buf;
  103.     *poutbuf_size = buf_size;
  104.     return next;
  105. }
  106.  
  107. AVCodecParser ff_aac_latm_parser = {
  108.     .codec_ids      = { AV_CODEC_ID_AAC_LATM },
  109.     .priv_data_size = sizeof(LATMParseContext),
  110.     .parser_parse   = latm_parse,
  111.     .parser_close   = ff_parse_close
  112. };
  113.