• Main Page
  • Related Pages
  • Modules
  • Data Structures
  • Files
  • File List
  • Globals

libavcodec/mpegvideo_parser.c

Go to the documentation of this file.
00001 /*
00002  * MPEG1 / MPEG2 video parser
00003  * Copyright (c) 2000,2001 Fabrice Bellard
00004  * Copyright (c) 2002-2004 Michael Niedermayer <michaelni@gmx.at>
00005  *
00006  * This file is part of FFmpeg.
00007  *
00008  * FFmpeg is free software; you can redistribute it and/or
00009  * modify it under the terms of the GNU Lesser General Public
00010  * License as published by the Free Software Foundation; either
00011  * version 2.1 of the License, or (at your option) any later version.
00012  *
00013  * FFmpeg is distributed in the hope that it will be useful,
00014  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00015  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00016  * Lesser General Public License for more details.
00017  *
00018  * You should have received a copy of the GNU Lesser General Public
00019  * License along with FFmpeg; if not, write to the Free Software
00020  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00021  */
00022 
00023 #include "parser.h"
00024 #include "mpegvideo.h"
00025 
00026 static void mpegvideo_extract_headers(AVCodecParserContext *s,
00027                                       AVCodecContext *avctx,
00028                                       const uint8_t *buf, int buf_size)
00029 {
00030     ParseContext1 *pc = s->priv_data;
00031     const uint8_t *buf_end;
00032     const uint8_t *buf_start= buf;
00033     uint32_t start_code;
00034     int frame_rate_index, ext_type, bytes_left;
00035     int frame_rate_ext_n, frame_rate_ext_d;
00036     int picture_structure, top_field_first, repeat_first_field, progressive_frame;
00037     int horiz_size_ext, vert_size_ext, bit_rate_ext;
00038 //FIXME replace the crap with get_bits()
00039     s->repeat_pict = 0;
00040     buf_end = buf + buf_size;
00041     while (buf < buf_end) {
00042         start_code= -1;
00043         buf= ff_find_start_code(buf, buf_end, &start_code);
00044         bytes_left = buf_end - buf;
00045         switch(start_code) {
00046         case PICTURE_START_CODE:
00047             ff_fetch_timestamp(s, buf-buf_start-4, 1);
00048 
00049             if (bytes_left >= 2) {
00050                 s->pict_type = (buf[1] >> 3) & 7;
00051             }
00052             break;
00053         case SEQ_START_CODE:
00054             if (bytes_left >= 7) {
00055                 pc->width  = (buf[0] << 4) | (buf[1] >> 4);
00056                 pc->height = ((buf[1] & 0x0f) << 8) | buf[2];
00057                 avcodec_set_dimensions(avctx, pc->width, pc->height);
00058                 frame_rate_index = buf[3] & 0xf;
00059                 pc->frame_rate.den = avctx->time_base.den = ff_frame_rate_tab[frame_rate_index].num;
00060                 pc->frame_rate.num = avctx->time_base.num = ff_frame_rate_tab[frame_rate_index].den;
00061                 avctx->bit_rate = ((buf[4]<<10) | (buf[5]<<2) | (buf[6]>>6))*400;
00062                 avctx->codec_id = CODEC_ID_MPEG1VIDEO;
00063                 avctx->sub_id = 1;
00064             }
00065             break;
00066         case EXT_START_CODE:
00067             if (bytes_left >= 1) {
00068                 ext_type = (buf[0] >> 4);
00069                 switch(ext_type) {
00070                 case 0x1: /* sequence extension */
00071                     if (bytes_left >= 6) {
00072                         horiz_size_ext = ((buf[1] & 1) << 1) | (buf[2] >> 7);
00073                         vert_size_ext = (buf[2] >> 5) & 3;
00074                         bit_rate_ext = ((buf[2] & 0x1F)<<7) | (buf[3]>>1);
00075                         frame_rate_ext_n = (buf[5] >> 5) & 3;
00076                         frame_rate_ext_d = (buf[5] & 0x1f);
00077                         pc->progressive_sequence = buf[1] & (1 << 3);
00078                         avctx->has_b_frames= !(buf[5] >> 7);
00079 
00080                         pc->width  |=(horiz_size_ext << 12);
00081                         pc->height |=( vert_size_ext << 12);
00082                         avctx->bit_rate += (bit_rate_ext << 18) * 400;
00083                         avcodec_set_dimensions(avctx, pc->width, pc->height);
00084                         avctx->time_base.den = pc->frame_rate.den * (frame_rate_ext_n + 1) * 2;
00085                         avctx->time_base.num = pc->frame_rate.num * (frame_rate_ext_d + 1);
00086                         avctx->codec_id = CODEC_ID_MPEG2VIDEO;
00087                         avctx->sub_id = 2; /* forces MPEG2 */
00088                     }
00089                     break;
00090                 case 0x8: /* picture coding extension */
00091                     if (bytes_left >= 5) {
00092                         picture_structure = buf[2]&3;
00093                         top_field_first = buf[3] & (1 << 7);
00094                         repeat_first_field = buf[3] & (1 << 1);
00095                         progressive_frame = buf[4] & (1 << 7);
00096 
00097                         /* check if we must repeat the frame */
00098                         s->repeat_pict = 1;
00099                         if (repeat_first_field) {
00100                             if (pc->progressive_sequence) {
00101                                 if (top_field_first)
00102                                     s->repeat_pict = 5;
00103                                 else
00104                                     s->repeat_pict = 3;
00105                             } else if (progressive_frame) {
00106                                 s->repeat_pict = 2;
00107                             }
00108                         }
00109                     }
00110                     break;
00111                 }
00112             }
00113             break;
00114         case -1:
00115             goto the_end;
00116         default:
00117             /* we stop parsing when we encounter a slice. It ensures
00118                that this function takes a negligible amount of time */
00119             if (start_code >= SLICE_MIN_START_CODE &&
00120                 start_code <= SLICE_MAX_START_CODE)
00121                 goto the_end;
00122             break;
00123         }
00124     }
00125  the_end: ;
00126 }
00127 
00128 static int mpegvideo_parse(AVCodecParserContext *s,
00129                            AVCodecContext *avctx,
00130                            const uint8_t **poutbuf, int *poutbuf_size,
00131                            const uint8_t *buf, int buf_size)
00132 {
00133     ParseContext1 *pc1 = s->priv_data;
00134     ParseContext *pc= &pc1->pc;
00135     int next;
00136 
00137     if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
00138         next= buf_size;
00139     }else{
00140         next= ff_mpeg1_find_frame_end(pc, buf, buf_size);
00141 
00142         if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
00143             *poutbuf = NULL;
00144             *poutbuf_size = 0;
00145             return buf_size;
00146         }
00147 
00148     }
00149     /* we have a full frame : we just parse the first few MPEG headers
00150        to have the full timing information. The time take by this
00151        function should be negligible for uncorrupted streams */
00152     mpegvideo_extract_headers(s, avctx, buf, buf_size);
00153 #if 0
00154     printf("pict_type=%d frame_rate=%0.3f repeat_pict=%d\n",
00155            s->pict_type, (double)avctx->time_base.den / avctx->time_base.num, s->repeat_pict);
00156 #endif
00157 
00158     *poutbuf = buf;
00159     *poutbuf_size = buf_size;
00160     return next;
00161 }
00162 
00163 static int mpegvideo_split(AVCodecContext *avctx,
00164                            const uint8_t *buf, int buf_size)
00165 {
00166     int i;
00167     uint32_t state= -1;
00168 
00169     for(i=0; i<buf_size; i++){
00170         state= (state<<8) | buf[i];
00171         if(state != 0x1B3 && state != 0x1B5 && state < 0x200 && state >= 0x100)
00172             return i-3;
00173     }
00174     return 0;
00175 }
00176 
00177 AVCodecParser mpegvideo_parser = {
00178     { CODEC_ID_MPEG1VIDEO, CODEC_ID_MPEG2VIDEO },
00179     sizeof(ParseContext1),
00180     NULL,
00181     mpegvideo_parse,
00182     ff_parse1_close,
00183 };

Generated on Sat Feb 16 2013 09:23:13 for ffmpeg by  doxygen 1.7.1