annotate ffmpeg/libavcodec/h261_parser.c @ 13:844d341cf643 tip

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/*
 * H261 parser
 * Copyright (c) 2002-2004 Michael Niedermayer <[e-mail]>
 * Copyright (c) 2004 Maarten Daniels
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * h261codec.
 */

#include "parser.h"

static int h261_find_frame_end(ParseContext *pc, AVCodecContext *avctx,
                               const uint8_t *buf, int buf_size)
{
    int vop_found, i, j;
    uint32_t state;

    vop_found = pc->frame_start_found;
    state     = pc->state;

    for (i = 0; i < buf_size && !vop_found; i++) {
        state = (state << 8) | buf[i];
        for (j = 0; j < 8; j++) {
            if (((state >> j) & 0xFFFFF0) == 0x000100) {
                vop_found = 1;
                break;
            }
        }
    }
    if (vop_found) {
        for (; i < buf_size; i++) {
            state = (state << 8) | buf[i];
            for (j = 0; j < 8; j++) {
                if (((state >> j) & 0xFFFFF0) == 0x000100) {
                    pc->frame_start_found = 0;
                    pc->state             = (state >> (3 * 8)) + 0xFF00;
                    return i - 2;
                }
            }
        }
    }

    pc->frame_start_found = vop_found;
    pc->state             = state;
    return END_NOT_FOUND;
}

static int h261_parse(AVCodecParserContext *s,
                      AVCodecContext *avctx,
                      const uint8_t **poutbuf, int *poutbuf_size,
                      const uint8_t *buf, int buf_size)
{
    ParseContext *pc = s->priv_data;
    int next;

    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
        next = buf_size;
    } else {
        next = h261_find_frame_end(pc, avctx, buf, buf_size);
        if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
            *poutbuf      = NULL;
            *poutbuf_size = 0;
            return buf_size;
        }
    }
    *poutbuf      = buf;
    *poutbuf_size = buf_size;
    return next;
}

AVCodecParser ff_h261_parser = {
    .codec_ids      = { AV_CODEC_ID_H261 },
    .priv_data_size = sizeof(ParseContext),
    .parser_parse   = h261_parse,
    .parser_close   = ff_parse_close,
};