FFmpeg4/libavcodec/mjpeg_parser.c

/*
 * MJPEG parser
 * Copyright (c) 2000, 2001 Fabrice Bellard
 * Copyright (c) 2003 Alex Beregszaszi
 * Copyright (c) 2003-2004 Michael Niedermayer
 *
 * 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
 * MJPEG parser.
 */

#include "parser.h"

typedef struct MJPEGParserContext{
    ParseContext pc;
    int size;
}MJPEGParserContext;

/**
 * Find the end of the current frame in the bitstream.
 * @return the position of the first byte of the next frame, or -1
 */
static int find_frame_end(MJPEGParserContext *m, const uint8_t *buf, int buf_size){
    ParseContext *pc= &m->pc;
    int vop_found, i;
    uint32_t state;

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

    i=0;
    if(!vop_found){
        for(i=0; i<buf_size;){
            state= (state<<8) | buf[i];
            if(state>=0xFFC00000 && state<=0xFFFEFFFF){
                if(state>=0xFFD8FFC0 && state<=0xFFD8FFFF){
                    i++;
                    vop_found=1;
                    break;
                }else if(state<0xFFD00000 || state>0xFFD9FFFF){
                    m->size= (state&0xFFFF)-1;
                }
            }
            if(m->size>0){
                int size= FFMIN(buf_size-i, m->size);
                i+=size;
                m->size-=size;
                state=0;
                continue;
            }else
                i++;
        }
    }

    if(vop_found){
        /* EOF considered as end of frame */
        if (buf_size == 0)
            return 0;
        for(; i<buf_size;){
            state= (state<<8) | buf[i];
            if(state>=0xFFC00000 && state<=0xFFFEFFFF){
                if(state>=0xFFD8FFC0 && state<=0xFFD8FFFF){
                    pc->frame_start_found=0;
                    pc->state=0;
                    return i-3;
                } else if(state<0xFFD00000 || state>0xFFD9FFFF){
                    m->size= (state&0xFFFF)-1;
                    if (m->size >= 0xF000)
                        m->size = 0;
                }
            }
            if(m->size>0){
                int size= FFMIN(buf_size-i, m->size);
                i+=size;
                m->size-=size;
                state=0;
                continue;
            }else
                i++;
        }
    }
    pc->frame_start_found= vop_found;
    pc->state= state;
    return END_NOT_FOUND;
}

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

    if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
        next= buf_size;
    }else{
        next= find_frame_end(m, 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_mjpeg_parser = {
    .codec_ids      = { AV_CODEC_ID_MJPEG, AV_CODEC_ID_JPEGLS },
    .priv_data_size = sizeof(MJPEGParserContext),
    .parser_parse   = jpeg_parse,
    .parser_close   = ff_parse_close,
};