FFmpeg: libavformat/mpeg.c Source File

00001 /*
00002  * MPEG1/2 demuxer
00003  * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
00004  *
00005  * This file is part of FFmpeg.
00006  *
00007  * FFmpeg is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * FFmpeg is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with FFmpeg; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00022 #include "avformat.h"
00023 #include "mpeg.h"
00024 
00025 //#define DEBUG_SEEK
00026 
00027 #undef NDEBUG
00028 #include <assert.h>
00029 
00030 /*********************************************/
00031 /* demux code */
00032 
00033 #define MAX_SYNC_SIZE 100000
00034 
00035 static int check_pes(uint8_t *p, uint8_t *end){
00036     int pes1;
00037     int pes2=      (p[3] & 0xC0) == 0x80
00038                 && (p[4] & 0xC0) != 0x40
00039                 &&((p[4] & 0xC0) == 0x00 || (p[4]&0xC0)>>2 == (p[6]&0xF0));
00040 
00041     for(p+=3; p<end && *p == 0xFF; p++);
00042     if((*p&0xC0) == 0x40) p+=2;
00043     if((*p&0xF0) == 0x20){
00044         pes1= p[0]&p[2]&p[4]&1;
00045     }else if((*p&0xF0) == 0x30){
00046         pes1= p[0]&p[2]&p[4]&p[5]&p[7]&p[9]&1;
00047     }else
00048         pes1 = *p == 0x0F;
00049 
00050     return pes1||pes2;
00051 }
00052 
00053 static int mpegps_probe(AVProbeData *p)
00054 {
00055     uint32_t code= -1;
00056     int sys=0, pspack=0, priv1=0, vid=0, audio=0, invalid=0;
00057     int i;
00058     int score=0;
00059 
00060     for(i=0; i<p->buf_size; i++){
00061         code = (code<<8) + p->buf[i];
00062         if ((code & 0xffffff00) == 0x100) {
00063             int pes= check_pes(p->buf+i, p->buf+p->buf_size);
00064 
00065             if(code == SYSTEM_HEADER_START_CODE) sys++;
00066             else if(code == PRIVATE_STREAM_1)    priv1++;
00067             else if(code == PACK_START_CODE)     pspack++;
00068             else if((code & 0xf0) == VIDEO_ID &&  pes) vid++;
00069             else if((code & 0xe0) == AUDIO_ID &&  pes) audio++;
00070 
00071             else if((code & 0xf0) == VIDEO_ID && !pes) invalid++;
00072             else if((code & 0xe0) == AUDIO_ID && !pes) invalid++;
00073         }
00074     }
00075 
00076     if(vid+audio > invalid)     /* invalid VDR files nd short PES streams */
00077         score= AVPROBE_SCORE_MAX/4;
00078 
00079 //av_log(NULL, AV_LOG_ERROR, "%d %d %d %d %d %d len:%d\n", sys, priv1, pspack,vid, audio, invalid, p->buf_size);
00080     if(sys>invalid && sys*9 <= pspack*10)
00081         return pspack > 2 ? AVPROBE_SCORE_MAX/2+2 : AVPROBE_SCORE_MAX/4; // +1 for .mpg
00082     if(pspack > invalid && (priv1+vid+audio)*10 >= pspack*9)
00083         return pspack > 2 ? AVPROBE_SCORE_MAX/2+2 : AVPROBE_SCORE_MAX/4; // +1 for .mpg
00084     if((!!vid ^ !!audio) && (audio > 4 || vid > 1) && !sys && !pspack && p->buf_size>2048 && vid + audio > invalid) /* PES stream */
00085         return (audio > 12 || vid > 3) ? AVPROBE_SCORE_MAX/2+2 : AVPROBE_SCORE_MAX/4;
00086 
00087     //02-Penguin.flac has sys:0 priv1:0 pspack:0 vid:0 audio:1
00088     //mp3_misidentified_2.mp3 has sys:0 priv1:0 pspack:0 vid:0 audio:6
00089     return score;
00090 }
00091 
00092 
00093 typedef struct MpegDemuxContext {
00094     int32_t header_state;
00095     unsigned char psm_es_type[256];
00096     int sofdec;
00097 } MpegDemuxContext;
00098 
00099 static int mpegps_read_header(AVFormatContext *s,
00100                               AVFormatParameters *ap)
00101 {
00102     MpegDemuxContext *m = s->priv_data;
00103     const char *sofdec = "Sofdec";
00104     int v, i = 0;
00105 
00106     m->header_state = 0xff;
00107     s->ctx_flags |= AVFMTCTX_NOHEADER;
00108 
00109     m->sofdec = -1;
00110     do {
00111         v = get_byte(s->pb);
00112         m->header_state = m->header_state << 8 | v;
00113         m->sofdec++;
00114     } while (v == sofdec[i] && i++ < 6);
00115 
00116     m->sofdec = (m->sofdec == 6) ? 1 : 0;
00117 
00118     /* no need to do more */
00119     return 0;
00120 }
00121 
00122 static int64_t get_pts(ByteIOContext *pb, int c)
00123 {
00124     uint8_t buf[5];
00125 
00126     buf[0] = c<0 ? get_byte(pb) : c;
00127     get_buffer(pb, buf+1, 4);
00128 
00129     return ff_parse_pes_pts(buf);
00130 }
00131 
00132 static int find_next_start_code(ByteIOContext *pb, int *size_ptr,
00133                                 int32_t *header_state)
00134 {
00135     unsigned int state, v;
00136     int val, n;
00137 
00138     state = *header_state;
00139     n = *size_ptr;
00140     while (n > 0) {
00141         if (url_feof(pb))
00142             break;
00143         v = get_byte(pb);
00144         n--;
00145         if (state == 0x000001) {
00146             state = ((state << 8) | v) & 0xffffff;
00147             val = state;
00148             goto found;
00149         }
00150         state = ((state << 8) | v) & 0xffffff;
00151     }
00152     val = -1;
00153  found:
00154     *header_state = state;
00155     *size_ptr = n;
00156     return val;
00157 }
00158 
00159 #if 0 /* unused, remove? */
00160 /* XXX: optimize */
00161 static int find_prev_start_code(ByteIOContext *pb, int *size_ptr)
00162 {
00163     int64_t pos, pos_start;
00164     int max_size, start_code;
00165 
00166     max_size = *size_ptr;
00167     pos_start = url_ftell(pb);
00168 
00169     /* in order to go faster, we fill the buffer */
00170     pos = pos_start - 16386;
00171     if (pos < 0)
00172         pos = 0;
00173     url_fseek(pb, pos, SEEK_SET);
00174     get_byte(pb);
00175 
00176     pos = pos_start;
00177     for(;;) {
00178         pos--;
00179         if (pos < 0 || (pos_start - pos) >= max_size) {
00180             start_code = -1;
00181             goto the_end;
00182         }
00183         url_fseek(pb, pos, SEEK_SET);
00184         start_code = get_be32(pb);
00185         if ((start_code & 0xffffff00) == 0x100)
00186             break;
00187     }
00188  the_end:
00189     *size_ptr = pos_start - pos;
00190     return start_code;
00191 }
00192 #endif
00193 
00200 static long mpegps_psm_parse(MpegDemuxContext *m, ByteIOContext *pb)
00201 {
00202     int psm_length, ps_info_length, es_map_length;
00203 
00204     psm_length = get_be16(pb);
00205     get_byte(pb);
00206     get_byte(pb);
00207     ps_info_length = get_be16(pb);
00208 
00209     /* skip program_stream_info */
00210     url_fskip(pb, ps_info_length);
00211     es_map_length = get_be16(pb);
00212 
00213     /* at least one es available? */
00214     while (es_map_length >= 4){
00215         unsigned char type      = get_byte(pb);
00216         unsigned char es_id     = get_byte(pb);
00217         uint16_t es_info_length = get_be16(pb);
00218         /* remember mapping from stream id to stream type */
00219         m->psm_es_type[es_id] = type;
00220         /* skip program_stream_info */
00221         url_fskip(pb, es_info_length);
00222         es_map_length -= 4 + es_info_length;
00223     }
00224     get_be32(pb); /* crc32 */
00225     return 2 + psm_length;
00226 }
00227 
00228 /* read the next PES header. Return its position in ppos
00229    (if not NULL), and its start code, pts and dts.
00230  */
00231 static int mpegps_read_pes_header(AVFormatContext *s,
00232                                   int64_t *ppos, int *pstart_code,
00233                                   int64_t *ppts, int64_t *pdts)
00234 {
00235     MpegDemuxContext *m = s->priv_data;
00236     int len, size, startcode, c, flags, header_len;
00237     int pes_ext, ext2_len, id_ext, skip;
00238     int64_t pts, dts;
00239     int64_t last_sync= url_ftell(s->pb);
00240 
00241  error_redo:
00242         url_fseek(s->pb, last_sync, SEEK_SET);
00243  redo:
00244         /* next start code (should be immediately after) */
00245         m->header_state = 0xff;
00246         size = MAX_SYNC_SIZE;
00247         startcode = find_next_start_code(s->pb, &size, &m->header_state);
00248         last_sync = url_ftell(s->pb);
00249     //printf("startcode=%x pos=0x%"PRIx64"\n", startcode, url_ftell(s->pb));
00250     if (startcode < 0){
00251         if(url_feof(s->pb))
00252             return AVERROR_EOF;
00253         //FIXME we should remember header_state
00254         return AVERROR(EAGAIN);
00255     }
00256 
00257     if (startcode == PACK_START_CODE)
00258         goto redo;
00259     if (startcode == SYSTEM_HEADER_START_CODE)
00260         goto redo;
00261     if (startcode == PADDING_STREAM) {
00262         url_fskip(s->pb, get_be16(s->pb));
00263         goto redo;
00264     }
00265     if (startcode == PRIVATE_STREAM_2) {
00266         len = get_be16(s->pb);
00267         if (!m->sofdec) {
00268             while (len-- >= 6) {
00269                 if (get_byte(s->pb) == 'S') {
00270                     uint8_t buf[5];
00271                     get_buffer(s->pb, buf, sizeof(buf));
00272                     m->sofdec = !memcmp(buf, "ofdec", 5);
00273                     len -= sizeof(buf);
00274                     break;
00275                 }
00276             }
00277             m->sofdec -= !m->sofdec;
00278         }
00279         url_fskip(s->pb, len);
00280         goto redo;
00281     }
00282     if (startcode == PROGRAM_STREAM_MAP) {
00283         mpegps_psm_parse(m, s->pb);
00284         goto redo;
00285     }
00286 
00287     /* find matching stream */
00288     if (!((startcode >= 0x1c0 && startcode <= 0x1df) ||
00289           (startcode >= 0x1e0 && startcode <= 0x1ef) ||
00290           (startcode == 0x1bd) || (startcode == 0x1fd)))
00291         goto redo;
00292     if (ppos) {
00293         *ppos = url_ftell(s->pb) - 4;
00294     }
00295     len = get_be16(s->pb);
00296     pts =
00297     dts = AV_NOPTS_VALUE;
00298     /* stuffing */
00299     for(;;) {
00300         if (len < 1)
00301             goto error_redo;
00302         c = get_byte(s->pb);
00303         len--;
00304         /* XXX: for mpeg1, should test only bit 7 */
00305         if (c != 0xff)
00306             break;
00307     }
00308     if ((c & 0xc0) == 0x40) {
00309         /* buffer scale & size */
00310         get_byte(s->pb);
00311         c = get_byte(s->pb);
00312         len -= 2;
00313     }
00314     if ((c & 0xe0) == 0x20) {
00315         dts = pts = get_pts(s->pb, c);
00316         len -= 4;
00317         if (c & 0x10){
00318             dts = get_pts(s->pb, -1);
00319             len -= 5;
00320         }
00321     } else if ((c & 0xc0) == 0x80) {
00322         /* mpeg 2 PES */
00323 #if 0 /* some streams have this field set for no apparent reason */
00324         if ((c & 0x30) != 0) {
00325             /* Encrypted multiplex not handled */
00326             goto redo;
00327         }
00328 #endif
00329         flags = get_byte(s->pb);
00330         header_len = get_byte(s->pb);
00331         len -= 2;
00332         if (header_len > len)
00333             goto error_redo;
00334         len -= header_len;
00335         if (flags & 0x80) {
00336             dts = pts = get_pts(s->pb, -1);
00337             header_len -= 5;
00338             if (flags & 0x40) {
00339                 dts = get_pts(s->pb, -1);
00340                 header_len -= 5;
00341             }
00342         }
00343         if (flags & 0x3f && header_len == 0){
00344             flags &= 0xC0;
00345             av_log(s, AV_LOG_WARNING, "Further flags set but no bytes left\n");
00346         }
00347         if (flags & 0x01) { /* PES extension */
00348             pes_ext = get_byte(s->pb);
00349             header_len--;
00350             /* Skip PES private data, program packet sequence counter and P-STD buffer */
00351             skip = (pes_ext >> 4) & 0xb;
00352             skip += skip & 0x9;
00353             if (pes_ext & 0x40 || skip > header_len){
00354                 av_log(s, AV_LOG_WARNING, "pes_ext %X is invalid\n", pes_ext);
00355                 pes_ext=skip=0;
00356             }
00357             url_fskip(s->pb, skip);
00358             header_len -= skip;
00359 
00360             if (pes_ext & 0x01) { /* PES extension 2 */
00361                 ext2_len = get_byte(s->pb);
00362                 header_len--;
00363                 if ((ext2_len & 0x7f) > 0) {
00364                     id_ext = get_byte(s->pb);
00365                     if ((id_ext & 0x80) == 0)
00366                         startcode = ((startcode & 0xff) << 8) | id_ext;
00367                     header_len--;
00368                 }
00369             }
00370         }
00371         if(header_len < 0)
00372             goto error_redo;
00373         url_fskip(s->pb, header_len);
00374     }
00375     else if( c!= 0xf )
00376         goto redo;
00377 
00378     if (startcode == PRIVATE_STREAM_1 && !m->psm_es_type[startcode & 0xff]) {
00379         startcode = get_byte(s->pb);
00380         len--;
00381         if (startcode >= 0x80 && startcode <= 0xcf) {
00382             /* audio: skip header */
00383             get_byte(s->pb);
00384             get_byte(s->pb);
00385             get_byte(s->pb);
00386             len -= 3;
00387             if (startcode >= 0xb0 && startcode <= 0xbf) {
00388                 /* MLP/TrueHD audio has a 4-byte header */
00389                 get_byte(s->pb);
00390                 len--;
00391             }
00392         }
00393     }
00394     if(len<0)
00395         goto error_redo;
00396     if(dts != AV_NOPTS_VALUE && ppos){
00397         int i;
00398         for(i=0; i<s->nb_streams; i++){
00399             if(startcode == s->streams[i]->id &&
00400                !url_is_streamed(s->pb) /* index useless on streams anyway */) {
00401                 ff_reduce_index(s, i);
00402                 av_add_index_entry(s->streams[i], *ppos, dts, 0, 0, AVINDEX_KEYFRAME /* FIXME keyframe? */);
00403             }
00404         }
00405     }
00406 
00407     *pstart_code = startcode;
00408     *ppts = pts;
00409     *pdts = dts;
00410     return len;
00411 }
00412 
00413 static int mpegps_read_packet(AVFormatContext *s,
00414                               AVPacket *pkt)
00415 {
00416     MpegDemuxContext *m = s->priv_data;
00417     AVStream *st;
00418     int len, startcode, i, es_type;
00419     enum CodecID codec_id = CODEC_ID_NONE;
00420     enum AVMediaType type;
00421     int64_t pts, dts, dummy_pos; //dummy_pos is needed for the index building to work
00422     uint8_t av_uninit(dvdaudio_substream_type);
00423 
00424  redo:
00425     len = mpegps_read_pes_header(s, &dummy_pos, &startcode, &pts, &dts);
00426     if (len < 0)
00427         return len;
00428 
00429     if(startcode == 0x1bd) {
00430         dvdaudio_substream_type = get_byte(s->pb);
00431         url_fskip(s->pb, 3);
00432         len -= 4;
00433     }
00434 
00435     /* now find stream */
00436     for(i=0;i<s->nb_streams;i++) {
00437         st = s->streams[i];
00438         if (st->id == startcode)
00439             goto found;
00440     }
00441 
00442     es_type = m->psm_es_type[startcode & 0xff];
00443     if(es_type > 0 && es_type != STREAM_TYPE_PRIVATE_DATA){
00444         if(es_type == STREAM_TYPE_VIDEO_MPEG1){
00445             codec_id = CODEC_ID_MPEG2VIDEO;
00446             type = AVMEDIA_TYPE_VIDEO;
00447         } else if(es_type == STREAM_TYPE_VIDEO_MPEG2){
00448             codec_id = CODEC_ID_MPEG2VIDEO;
00449             type = AVMEDIA_TYPE_VIDEO;
00450         } else if(es_type == STREAM_TYPE_AUDIO_MPEG1 ||
00451                   es_type == STREAM_TYPE_AUDIO_MPEG2){
00452             codec_id = CODEC_ID_MP3;
00453             type = AVMEDIA_TYPE_AUDIO;
00454         } else if(es_type == STREAM_TYPE_AUDIO_AAC){
00455             codec_id = CODEC_ID_AAC;
00456             type = AVMEDIA_TYPE_AUDIO;
00457         } else if(es_type == STREAM_TYPE_VIDEO_MPEG4){
00458             codec_id = CODEC_ID_MPEG4;
00459             type = AVMEDIA_TYPE_VIDEO;
00460         } else if(es_type == STREAM_TYPE_VIDEO_H264){
00461             codec_id = CODEC_ID_H264;
00462             type = AVMEDIA_TYPE_VIDEO;
00463         } else if(es_type == STREAM_TYPE_AUDIO_AC3){
00464             codec_id = CODEC_ID_AC3;
00465             type = AVMEDIA_TYPE_AUDIO;
00466         } else {
00467             goto skip;
00468         }
00469     } else if (startcode >= 0x1e0 && startcode <= 0x1ef) {
00470         static const unsigned char avs_seqh[4] = { 0, 0, 1, 0xb0 };
00471         unsigned char buf[8];
00472         get_buffer(s->pb, buf, 8);
00473         url_fseek(s->pb, -8, SEEK_CUR);
00474         if(!memcmp(buf, avs_seqh, 4) && (buf[6] != 0 || buf[7] != 1))
00475             codec_id = CODEC_ID_CAVS;
00476         else
00477             codec_id = CODEC_ID_PROBE;
00478         type = AVMEDIA_TYPE_VIDEO;
00479     } else if (startcode >= 0x1c0 && startcode <= 0x1df) {
00480         type = AVMEDIA_TYPE_AUDIO;
00481         codec_id = m->sofdec > 0 ? CODEC_ID_ADPCM_ADX : CODEC_ID_MP2;
00482     } else if (startcode >= 0x80 && startcode <= 0x87) {
00483         type = AVMEDIA_TYPE_AUDIO;
00484         codec_id = CODEC_ID_AC3;
00485     } else if (  ( startcode >= 0x88 && startcode <= 0x8f)
00486                ||( startcode >= 0x98 && startcode <= 0x9f)) {
00487         /* 0x90 - 0x97 is reserved for SDDS in DVD specs */
00488         type = AVMEDIA_TYPE_AUDIO;
00489         codec_id = CODEC_ID_DTS;
00490     } else if (startcode >= 0xa0 && startcode <= 0xaf) {
00491         type = AVMEDIA_TYPE_AUDIO;
00492         /* 16 bit form will be handled as CODEC_ID_PCM_S16BE */
00493         codec_id = CODEC_ID_PCM_DVD;
00494     } else if (startcode >= 0xb0 && startcode <= 0xbf) {
00495         type = AVMEDIA_TYPE_AUDIO;
00496         codec_id = CODEC_ID_TRUEHD;
00497     } else if (startcode >= 0xc0 && startcode <= 0xcf) {
00498         /* Used for both AC-3 and E-AC-3 in EVOB files */
00499         type = AVMEDIA_TYPE_AUDIO;
00500         codec_id = CODEC_ID_AC3;
00501     } else if (startcode >= 0x20 && startcode <= 0x3f) {
00502         type = AVMEDIA_TYPE_SUBTITLE;
00503         codec_id = CODEC_ID_DVD_SUBTITLE;
00504     } else if (startcode >= 0xfd55 && startcode <= 0xfd5f) {
00505         type = AVMEDIA_TYPE_VIDEO;
00506         codec_id = CODEC_ID_VC1;
00507     } else if (startcode == 0x1bd) {
00508         // check dvd audio substream type
00509         type = AVMEDIA_TYPE_AUDIO;
00510         switch(dvdaudio_substream_type & 0xe0) {
00511         case 0xa0:  codec_id = CODEC_ID_PCM_DVD;
00512                     break;
00513         case 0x80:  if((dvdaudio_substream_type & 0xf8) == 0x88)
00514                          codec_id = CODEC_ID_DTS;
00515                     else codec_id = CODEC_ID_AC3;
00516                     break;
00517         default:    av_log(s, AV_LOG_ERROR, "Unknown 0x1bd sub-stream\n");
00518                     goto skip;
00519         }
00520     } else {
00521     skip:
00522         /* skip packet */
00523         url_fskip(s->pb, len);
00524         goto redo;
00525     }
00526     /* no stream found: add a new stream */
00527     st = av_new_stream(s, startcode);
00528     if (!st)
00529         goto skip;
00530     st->codec->codec_type = type;
00531     st->codec->codec_id = codec_id;
00532     if (codec_id != CODEC_ID_PCM_S16BE)
00533         st->need_parsing = AVSTREAM_PARSE_FULL;
00534  found:
00535     if(st->discard >= AVDISCARD_ALL)
00536         goto skip;
00537     if ((startcode >= 0xa0 && startcode <= 0xaf) ||
00538         (startcode == 0x1bd && ((dvdaudio_substream_type & 0xe0) == 0xa0))) {
00539         int b1, freq;
00540 
00541         /* for LPCM, we just skip the header and consider it is raw
00542            audio data */
00543         if (len <= 3)
00544             goto skip;
00545         get_byte(s->pb); /* emphasis (1), muse(1), reserved(1), frame number(5) */
00546         b1 = get_byte(s->pb); /* quant (2), freq(2), reserved(1), channels(3) */
00547         get_byte(s->pb); /* dynamic range control (0x80 = off) */
00548         len -= 3;
00549         freq = (b1 >> 4) & 3;
00550         st->codec->sample_rate = lpcm_freq_tab[freq];
00551         st->codec->channels = 1 + (b1 & 7);
00552         st->codec->bits_per_coded_sample = 16 + ((b1 >> 6) & 3) * 4;
00553         st->codec->bit_rate = st->codec->channels *
00554                               st->codec->sample_rate *
00555                               st->codec->bits_per_coded_sample;
00556         if (st->codec->bits_per_coded_sample == 16)
00557             st->codec->codec_id = CODEC_ID_PCM_S16BE;
00558         else if (st->codec->bits_per_coded_sample == 28)
00559             return AVERROR(EINVAL);
00560     }
00561     av_new_packet(pkt, len);
00562     get_buffer(s->pb, pkt->data, pkt->size);
00563     pkt->pts = pts;
00564     pkt->dts = dts;
00565     pkt->pos = dummy_pos;
00566     pkt->stream_index = st->index;
00567 #if 0
00568     av_log(s, AV_LOG_DEBUG, "%d: pts=%0.3f dts=%0.3f size=%d\n",
00569            pkt->stream_index, pkt->pts / 90000.0, pkt->dts / 90000.0, pkt->size);
00570 #endif
00571 
00572     return 0;
00573 }
00574 
00575 static int64_t mpegps_read_dts(AVFormatContext *s, int stream_index,
00576                                int64_t *ppos, int64_t pos_limit)
00577 {
00578     int len, startcode;
00579     int64_t pos, pts, dts;
00580 
00581     pos = *ppos;
00582 #ifdef DEBUG_SEEK
00583     printf("read_dts: pos=0x%"PRIx64" next=%d -> ", pos, find_next);
00584 #endif
00585     if (url_fseek(s->pb, pos, SEEK_SET) < 0)
00586         return AV_NOPTS_VALUE;
00587 
00588     for(;;) {
00589         len = mpegps_read_pes_header(s, &pos, &startcode, &pts, &dts);
00590         if (len < 0) {
00591 #ifdef DEBUG_SEEK
00592             printf("none (ret=%d)\n", len);
00593 #endif
00594             return AV_NOPTS_VALUE;
00595         }
00596         if (startcode == s->streams[stream_index]->id &&
00597             dts != AV_NOPTS_VALUE) {
00598             break;
00599         }
00600         url_fskip(s->pb, len);
00601     }
00602 #ifdef DEBUG_SEEK
00603     printf("pos=0x%"PRIx64" dts=0x%"PRIx64" %0.3f\n", pos, dts, dts / 90000.0);
00604 #endif
00605     *ppos = pos;
00606     return dts;
00607 }
00608 
00609 AVInputFormat mpegps_demuxer = {
00610     "mpeg",
00611     NULL_IF_CONFIG_SMALL("MPEG-PS format"),
00612     sizeof(MpegDemuxContext),
00613     mpegps_probe,
00614     mpegps_read_header,
00615     mpegps_read_packet,
00616     NULL,
00617     NULL, //mpegps_read_seek,
00618     mpegps_read_dts,
00619     .flags = AVFMT_SHOW_IDS|AVFMT_TS_DISCONT,
00620 };