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ffmpeg / libavcodec / latm_parser.c @ 2912e87a

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/*
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 * copyright (c) 2008 Paul Kendall <paul@kcbbs.gen.nz>
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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/**
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 * @file
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 * AAC LATM parser
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 */
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#include <stdint.h>
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#include "parser.h"
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#define LATM_HEADER     0x56e000        // 0x2b7 (11 bits)
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#define LATM_MASK       0xFFE000        // top 11 bits
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#define LATM_SIZE_MASK  0x001FFF        // bottom 13 bits
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typedef struct LATMParseContext{
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    ParseContext pc;
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    int count;
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} LATMParseContext;
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/**
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 * finds the end of the current frame in the bitstream.
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 * @return the position of the first byte of the next frame, or -1
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 */
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static int latm_find_frame_end(AVCodecParserContext *s1, const uint8_t *buf,
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                               int buf_size)
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{
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    LATMParseContext *s = s1->priv_data;
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    ParseContext *pc    = &s->pc;
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    int pic_found, i;
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    uint32_t state;
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    pic_found = pc->frame_start_found;
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    state     = pc->state;
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    i = 0;
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    if (!pic_found) {
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        for (i = 0; i < buf_size; i++) {
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            state = (state<<8) | buf[i];
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            if ((state & LATM_MASK) == LATM_HEADER) {
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                i++;
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                s->count  = -i;
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                pic_found = 1;
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                break;
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            }
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        }
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    }
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    if (pic_found) {
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        /* EOF considered as end of frame */
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        if (buf_size == 0)
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            return 0;
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        if ((state & LATM_SIZE_MASK) - s->count <= buf_size) {
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            pc->frame_start_found = 0;
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            pc->state             = -1;
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            return (state & LATM_SIZE_MASK) - s->count;
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        }
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    }
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    s->count             += buf_size;
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    pc->frame_start_found = pic_found;
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    pc->state             = state;
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    return END_NOT_FOUND;
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}
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static int latm_parse(AVCodecParserContext *s1, AVCodecContext *avctx,
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                      const uint8_t **poutbuf, int *poutbuf_size,
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                      const uint8_t *buf, int buf_size)
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{
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    LATMParseContext *s = s1->priv_data;
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    ParseContext *pc    = &s->pc;
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    int next;
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    if (s1->flags & PARSER_FLAG_COMPLETE_FRAMES) {
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        next = buf_size;
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    } else {
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        next = latm_find_frame_end(s1, buf, buf_size);
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        if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
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            *poutbuf      = NULL;
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            *poutbuf_size = 0;
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            return buf_size;
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        }
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    }
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    *poutbuf      = buf;
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    *poutbuf_size = buf_size;
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    return next;
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}
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AVCodecParser ff_aac_latm_parser = {
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    { CODEC_ID_AAC_LATM },
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    sizeof(LATMParseContext),
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    NULL,
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    latm_parse,
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    ff_parse_close
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};