libavcodec/latm_parser.c

   1 /*
   2  * copyright (c) 2008 Paul Kendall <paul@kcbbs.gen.nz>
   3  *
   4  * This file is part of Libav.
   5  *
   6  * Libav 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  * Libav 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 Libav; 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     i = 0;
  54     if (!pic_found) {
  55         for (i = 0; i < buf_size; i++) {
  56             state = (state<<8) | buf[i];
  57             if ((state & LATM_MASK) == LATM_HEADER) {
  58                 i++;
  59                 s->count  = -i;
  60                 pic_found = 1;
  61                 break;
  62             }
  63         }
  64     }
  65
  66     if (pic_found) {
  67         /* EOF considered as end of frame */
  68         if (buf_size == 0)
  69             return 0;
  70         if ((state & LATM_SIZE_MASK) - s->count <= buf_size) {
  71             pc->frame_start_found = 0;
  72             pc->state             = -1;
  73             return (state & LATM_SIZE_MASK) - s->count;
  74         }
  75     }
  76
  77     s->count             += buf_size;
  78     pc->frame_start_found = pic_found;
  79     pc->state             = state;
  80
  81     return END_NOT_FOUND;
  82 }
  83
  84 static int latm_parse(AVCodecParserContext *s1, AVCodecContext *avctx,
  85                       const uint8_t **poutbuf, int *poutbuf_size,
  86                       const uint8_t *buf, int buf_size)
  87 {
  88     LATMParseContext *s = s1->priv_data;
  89     ParseContext *pc    = &s->pc;
  90     int next;
  91
  92     if (s1->flags & PARSER_FLAG_COMPLETE_FRAMES) {
  93         next = buf_size;
  94     } else {
  95         next = latm_find_frame_end(s1, buf, buf_size);
  96
  97         if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
  98             *poutbuf      = NULL;
  99             *poutbuf_size = 0;
 100             return buf_size;
 101         }
 102     }
 103     *poutbuf      = buf;
 104     *poutbuf_size = buf_size;
 105     return next;
 106 }
 107
 108 AVCodecParser ff_aac_latm_parser = {
 109     .codec_ids      = { AV_CODEC_ID_AAC_LATM },
 110     .priv_data_size = sizeof(LATMParseContext),
 111     .parser_parse   = latm_parse,
 112     .parser_close   = ff_parse_close
 113 };