git.sesse.net Git - vlc/blob - modules/packetizer/mpegvideo.c

   1 /*****************************************************************************
   2  * mpegvideo.c: parse and packetize an MPEG1/2 video stream
   3  *****************************************************************************
   4  * Copyright (C) 2001-2006 the VideoLAN team
   5  * $Id$
   6  *
   7  * Authors: Laurent Aimar <fenrir@via.ecp.fr>
   8  *          Eric Petit <titer@videolan.org>
   9  *          Gildas Bazin <gbazin@videolan.org>
  10  *          Jean-Paul Saman <jpsaman #_at_# m2x dot nl>
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software
  24  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  25  *****************************************************************************/
  26
  27 /*****************************************************************************
  28  * Problem with this implementation:
  29  *
  30  * Although we should time-stamp each picture with a PTS, this isn't possible
  31  * with the current implementation.
  32  * The problem comes from the fact that for non-low-delay streams we can't
  33  * calculate the PTS of pictures used as backward reference. Even the temporal
  34  * reference number doesn't help here because all the pictures don't
  35  * necessarily have the same duration (eg. 3:2 pulldown).
  36  *
  37  * However this doesn't really matter as far as the MPEG muxers are concerned
  38  * because they allow having empty PTS fields. --gibalou
  39  *****************************************************************************/
  40
  41 /*****************************************************************************
  42  * Preamble
  43  *****************************************************************************/
  44 #include <stdlib.h>                                      /* malloc(), free() */
  45
  46 #include <vlc/vlc.h>
  47 #include <vlc/decoder.h>
  48 #include <vlc/input.h>
  49
  50 #include "vlc_block_helper.h"
  51
  52 #define SYNC_INTRAFRAME_TEXT N_("Sync on Intra Frame")
  53 #define SYNC_INTRAFRAME_LONGTEXT N_("Normally the packetizer would " \
  54     "sync on the next full frame. This flags instructs the packetizer " \
  55     "to sync on the first Intra Frame found.")
  56
  57 /*****************************************************************************
  58  * Module descriptor
  59  *****************************************************************************/
  60 static int  Open ( vlc_object_t * );
  61 static void Close( vlc_object_t * );
  62
  63 vlc_module_begin();
  64     set_category( CAT_SOUT );
  65     set_subcategory( SUBCAT_SOUT_PACKETIZER );
  66     set_description( _("MPEG-I/II video packetizer") );
  67     set_capability( "packetizer", 50 );
  68     set_callbacks( Open, Close );
  69
  70     add_bool( "packetizer-mpegvideo-sync-iframe", 0, NULL, SYNC_INTRAFRAME_TEXT,
  71               SYNC_INTRAFRAME_LONGTEXT, VLC_TRUE );
  72 vlc_module_end();
  73
  74 /*****************************************************************************
  75  * Local prototypes
  76  *****************************************************************************/
  77 static block_t *Packetize( decoder_t *, block_t ** );
  78 static block_t *ParseMPEGBlock( decoder_t *, block_t * );
  79
  80 struct decoder_sys_t
  81 {
  82     /*
  83      * Input properties
  84      */
  85     block_bytestream_t bytestream;
  86     int i_state;
  87     int i_offset;
  88     uint8_t p_startcode[3];
  89
  90     /* Sequence header and extension */
  91     block_t *p_seq;
  92     block_t *p_ext;
  93
  94     /* Current frame being built */
  95     block_t    *p_frame;
  96     block_t    **pp_last;
  97
  98     vlc_bool_t b_frame_slice;
  99     mtime_t i_pts;
 100     mtime_t i_dts;
 101
 102     /* Sequence properties */
 103     int         i_frame_rate;
 104     int         i_frame_rate_base;
 105     vlc_bool_t  b_seq_progressive;
 106     vlc_bool_t  b_low_delay;
 107     int         i_aspect_ratio_info;
 108     vlc_bool_t  b_inited;
 109
 110     /* Picture properties */
 111     int i_temporal_ref;
 112     int i_picture_type;
 113     int i_picture_structure;
 114     int i_top_field_first;
 115     int i_repeat_first_field;
 116     int i_progressive_frame;
 117
 118     mtime_t i_interpolated_dts;
 119     mtime_t i_old_duration;
 120     mtime_t i_last_ref_pts;
 121     vlc_bool_t b_second_field;
 122
 123     /* Number of pictures since last sequence header */
 124     int i_seq_old;
 125
 126     /* Sync behaviour */
 127     vlc_bool_t  b_sync_on_intra_frame;
 128     vlc_bool_t  b_discontinuity;
 129 };
 130
 131 enum {
 132     STATE_NOSYNC,
 133     STATE_NEXT_SYNC
 134 };
 135
 136 /*****************************************************************************
 137  * Open:
 138  *****************************************************************************/
 139 static int Open( vlc_object_t *p_this )
 140 {
 141     decoder_t *p_dec = (decoder_t*)p_this;
 142     decoder_sys_t *p_sys;
 143
 144     if( p_dec->fmt_in.i_codec != VLC_FOURCC( 'm', 'p', 'g', '1' ) &&
 145         p_dec->fmt_in.i_codec != VLC_FOURCC( 'm', 'p', 'g', '2' ) &&
 146         p_dec->fmt_in.i_codec != VLC_FOURCC( 'm', 'p', 'g', 'v' ) )
 147     {
 148         return VLC_EGENERIC;
 149     }
 150
 151     es_format_Init( &p_dec->fmt_out, VIDEO_ES, VLC_FOURCC('m','p','g','v') );
 152     p_dec->pf_packetize = Packetize;
 153
 154     p_dec->p_sys = p_sys = malloc( sizeof( decoder_sys_t ) );
 155
 156     /* Misc init */
 157     p_sys->i_state = STATE_NOSYNC;
 158     p_sys->bytestream = block_BytestreamInit( p_dec );
 159     p_sys->p_startcode[0] = 0;
 160     p_sys->p_startcode[1] = 0;
 161     p_sys->p_startcode[2] = 1;
 162     p_sys->i_offset = 0;
 163
 164     p_sys->p_seq = NULL;
 165     p_sys->p_ext = NULL;
 166     p_sys->p_frame = NULL;
 167     p_sys->pp_last = &p_sys->p_frame;
 168     p_sys->b_frame_slice = VLC_FALSE;
 169
 170     p_sys->i_dts = p_sys->i_pts = 0;
 171
 172     p_sys->i_frame_rate = 1;
 173     p_sys->i_frame_rate_base = 1;
 174     p_sys->b_seq_progressive = VLC_TRUE;
 175     p_sys->b_low_delay = VLC_TRUE;
 176     p_sys->i_seq_old = 0;
 177
 178     p_sys->i_temporal_ref = 0;
 179     p_sys->i_picture_type = 0;
 180     p_sys->i_picture_structure = 0x03; /* frame */
 181     p_sys->i_top_field_first = 0;
 182     p_sys->i_repeat_first_field = 0;
 183     p_sys->i_progressive_frame = 0;
 184     p_sys->b_inited = 0;
 185
 186     p_sys->i_interpolated_dts = 0;
 187     p_sys->i_old_duration = 0;
 188     p_sys->i_last_ref_pts = 0;
 189     p_sys->b_second_field = 0;
 190
 191     p_sys->b_discontinuity = VLC_FALSE;
 192     p_sys->b_sync_on_intra_frame = var_CreateGetBool( p_dec, "packetizer-mpegvideo-sync-iframe" );
 193     if( p_sys->b_sync_on_intra_frame )
 194         msg_Dbg( p_dec, "syncing on intra frame now" );
 195
 196     return VLC_SUCCESS;
 197 }
 198
 199 /*****************************************************************************
 200  * Close:
 201  *****************************************************************************/
 202 static void Close( vlc_object_t *p_this )
 203 {
 204     decoder_t     *p_dec = (decoder_t*)p_this;
 205     decoder_sys_t *p_sys = p_dec->p_sys;
 206
 207     block_BytestreamRelease( &p_sys->bytestream );
 208
 209     if( p_sys->p_seq )
 210     {
 211         block_Release( p_sys->p_seq );
 212     }
 213     if( p_sys->p_ext )
 214     {
 215         block_Release( p_sys->p_ext );
 216     }
 217     if( p_sys->p_frame )
 218     {
 219         block_ChainRelease( p_sys->p_frame );
 220     }
 221
 222     var_Destroy( p_dec, "packetizer-mpegvideo-sync-iframe" );
 223
 224     free( p_sys );
 225 }
 226
 227 /*****************************************************************************
 228  * Packetize:
 229  *****************************************************************************/
 230 static block_t *Packetize( decoder_t *p_dec, block_t **pp_block )
 231 {
 232     decoder_sys_t *p_sys = p_dec->p_sys;
 233     block_t       *p_pic;
 234
 235     if( pp_block == NULL || *pp_block == NULL )
 236     {
 237         return NULL;
 238     }
 239
 240     if( (*pp_block)->i_flags & (BLOCK_FLAG_DISCONTINUITY|BLOCK_FLAG_CORRUPTED) )
 241     {
 242         p_sys->i_state = STATE_NOSYNC;
 243         p_sys->b_discontinuity = VLC_TRUE;
 244         if( p_sys->p_frame )
 245             block_ChainRelease( p_sys->p_frame );
 246         p_sys->p_frame = NULL;
 247         p_sys->pp_last = &p_sys->p_frame;
 248         p_sys->b_frame_slice = VLC_FALSE;
 249         block_Release( *pp_block );
 250         return NULL;
 251     }
 252
 253     block_BytestreamPush( &p_sys->bytestream, *pp_block );
 254
 255     while( 1 )
 256     {
 257         switch( p_sys->i_state )
 258         {
 259
 260         case STATE_NOSYNC:
 261             if( block_FindStartcodeFromOffset( &p_sys->bytestream,
 262                     &p_sys->i_offset, p_sys->p_startcode, 3 ) == VLC_SUCCESS )
 263             {
 264                 p_sys->i_state = STATE_NEXT_SYNC;
 265             }
 266
 267             if( p_sys->i_offset )
 268             {
 269                 block_SkipBytes( &p_sys->bytestream, p_sys->i_offset );
 270                 p_sys->i_offset = 0;
 271                 block_BytestreamFlush( &p_sys->bytestream );
 272             }
 273
 274             if( p_sys->i_state != STATE_NEXT_SYNC )
 275             {
 276                 /* Need more data */
 277                 return NULL;
 278             }
 279
 280             p_sys->i_offset = 1; /* To find next startcode */
 281
 282         case STATE_NEXT_SYNC:
 283             /* TODO: If p_block == NULL, flush the buffer without checking the
 284              * next sync word */
 285
 286             /* Find the next startcode */
 287             if( block_FindStartcodeFromOffset( &p_sys->bytestream,
 288                     &p_sys->i_offset, p_sys->p_startcode, 3 ) != VLC_SUCCESS )
 289             {
 290                 /* Need more data */
 291                 return NULL;
 292             }
 293
 294             /* Get the new fragment and set the pts/dts */
 295             p_pic = block_New( p_dec, p_sys->i_offset );
 296             block_BytestreamFlush( &p_sys->bytestream );
 297             p_pic->i_pts = p_sys->bytestream.p_block->i_pts;
 298             p_pic->i_dts = p_sys->bytestream.p_block->i_dts;
 299
 300             block_GetBytes( &p_sys->bytestream, p_pic->p_buffer,
 301                             p_pic->i_buffer );
 302
 303             /* don't reuse the same timestamps several times */
 304             if( p_pic->i_buffer >= 4 && p_pic->p_buffer[3] == 0x00 )
 305             {
 306                 /* We have a picture start code */
 307                 p_sys->bytestream.p_block->i_pts = 0;
 308                 p_sys->bytestream.p_block->i_dts = 0;
 309             }
 310
 311             p_sys->i_offset = 0;
 312
 313             /* Get picture if any */
 314             if( !( p_pic = ParseMPEGBlock( p_dec, p_pic ) ) )
 315             {
 316                 p_sys->i_state = STATE_NOSYNC;
 317                 break;
 318             }
 319
 320             /* If a discontinuity has been encountered, then wait till
 321              * the next Intra frame before continuing with packetizing */
 322             if( p_sys->b_discontinuity &&
 323                 p_sys->b_sync_on_intra_frame )
 324             {
 325                 if( p_pic->i_flags & BLOCK_FLAG_TYPE_I )
 326                 {
 327                     msg_Dbg( p_dec, "synced on intra frame" );
 328                     p_sys->b_discontinuity = VLC_FALSE;
 329                     p_pic->i_flags |= BLOCK_FLAG_DISCONTINUITY;
 330                 }
 331                 else
 332                 {
 333                     msg_Dbg( p_dec, "waiting on intra frame" );
 334                     p_sys->i_state = STATE_NOSYNC;
 335                     block_Release( p_pic );
 336                     break;
 337                 }
 338             }
 339
 340             /* We've just started the stream, wait for the first PTS.
 341              * We discard here so we can still get the sequence header. */
 342             if( p_sys->i_dts <= 0 && p_sys->i_pts <= 0 &&
 343                 p_sys->i_interpolated_dts <= 0 )
 344             {
 345                 msg_Dbg( p_dec, "need a starting pts/dts" );
 346                 p_sys->i_state = STATE_NOSYNC;
 347                 block_Release( p_pic );
 348                 break;
 349             }
 350
 351             /* When starting the stream we can have the first frame with
 352              * a null DTS (i_interpolated_pts is initialized to 0) */
 353             if( !p_pic->i_dts ) p_pic->i_dts = p_pic->i_pts;
 354
 355             /* So p_block doesn't get re-added several times */
 356             *pp_block = block_BytestreamPop( &p_sys->bytestream );
 357
 358             p_sys->i_state = STATE_NOSYNC;
 359
 360             return p_pic;
 361         }
 362     }
 363 }
 364
 365 /*****************************************************************************
 366  * ParseMPEGBlock: Re-assemble fragments into a block containing a picture
 367  *****************************************************************************/
 368 static block_t *ParseMPEGBlock( decoder_t *p_dec, block_t *p_frag )
 369 {
 370     decoder_sys_t *p_sys = p_dec->p_sys;
 371     block_t *p_pic = NULL;
 372
 373     /*
 374      * Check if previous picture is finished
 375      */
 376     if( ( p_sys->b_frame_slice &&
 377           (p_frag->p_buffer[3] == 0x00 || p_frag->p_buffer[3] > 0xaf) ) &&
 378           p_sys->p_seq == NULL )
 379     {
 380         /* We have a picture but without a sequence header we can't
 381          * do anything */
 382         msg_Dbg( p_dec, "waiting for sequence start" );
 383         if( p_sys->p_frame ) block_ChainRelease( p_sys->p_frame );
 384         p_sys->p_frame = NULL;
 385         p_sys->pp_last = &p_sys->p_frame;
 386         p_sys->b_frame_slice = VLC_FALSE;
 387
 388     }
 389     else if( p_sys->b_frame_slice &&
 390              (p_frag->p_buffer[3] == 0x00 || p_frag->p_buffer[3] > 0xaf) )
 391     {
 392         mtime_t i_duration;
 393
 394         p_pic = block_ChainGather( p_sys->p_frame );
 395
 396         i_duration = (mtime_t)( 1000000 * p_sys->i_frame_rate_base /
 397                                 p_sys->i_frame_rate );
 398
 399         if( !p_sys->b_seq_progressive && p_sys->i_picture_structure != 0x03 )
 400         {
 401             i_duration /= 2;
 402         }
 403
 404         if( p_sys->b_seq_progressive )
 405         {
 406             if( p_sys->i_top_field_first == 0 &&
 407                 p_sys->i_repeat_first_field == 1 )
 408             {
 409                 i_duration *= 2;
 410             }
 411             else if( p_sys->i_top_field_first == 1 &&
 412                      p_sys->i_repeat_first_field == 1 )
 413             {
 414                 i_duration *= 3;
 415             }
 416         }
 417         else
 418         {
 419             if( p_sys->i_picture_structure == 0x03 )
 420             {
 421                 if( p_sys->i_progressive_frame && p_sys->i_repeat_first_field )
 422                 {
 423                     i_duration += i_duration / 2;
 424                 }
 425             }
 426         }
 427
 428         if( p_sys->b_low_delay || p_sys->i_picture_type == 0x03 )
 429         {
 430             /* Trivial case (DTS == PTS) */
 431             /* Correct interpolated dts when we receive a new pts/dts */
 432             if( p_sys->i_pts > 0 ) p_sys->i_interpolated_dts = p_sys->i_pts;
 433             if( p_sys->i_dts > 0 ) p_sys->i_interpolated_dts = p_sys->i_dts;
 434         }
 435         else
 436         {
 437             /* Correct interpolated dts when we receive a new pts/dts */
 438             if( p_sys->i_last_ref_pts > 0 && !p_sys->b_second_field )
 439                 p_sys->i_interpolated_dts = p_sys->i_last_ref_pts;
 440             if( p_sys->i_dts > 0 ) p_sys->i_interpolated_dts = p_sys->i_dts;
 441
 442             if( !p_sys->b_second_field )
 443                 p_sys->i_last_ref_pts = p_sys->i_pts;
 444         }
 445
 446         p_pic->i_dts = p_sys->i_interpolated_dts;
 447         p_sys->i_interpolated_dts += i_duration;
 448
 449         /* Set PTS only if we have a B frame or if it comes from the stream */
 450         if( p_sys->i_pts > 0 )
 451         {
 452             p_pic->i_pts = p_sys->i_pts;
 453         }
 454         else if( p_sys->i_picture_type == 0x03 )
 455         {
 456             p_pic->i_pts = p_pic->i_dts;
 457         }
 458         else
 459         {
 460             p_pic->i_pts = 0;
 461         }
 462
 463         switch ( p_sys->i_picture_type )
 464         {
 465         case 0x01:
 466             p_pic->i_flags |= BLOCK_FLAG_TYPE_I;
 467             break;
 468         case 0x02:
 469             p_pic->i_flags |= BLOCK_FLAG_TYPE_P;
 470             break;
 471         case 0x03:
 472             p_pic->i_flags |= BLOCK_FLAG_TYPE_B;
 473             break;
 474         }
 475
 476         p_pic->i_length = p_sys->i_interpolated_dts - p_pic->i_dts;
 477
 478 #if 0
 479         msg_Dbg( p_dec, "pic: type=%d dts="I64Fd" pts-dts="I64Fd,
 480         p_sys->i_picture_type, p_pic->i_dts, p_pic->i_pts - p_pic->i_dts);
 481 #endif
 482
 483         /* Reset context */
 484         p_sys->p_frame = NULL;
 485         p_sys->pp_last = &p_sys->p_frame;
 486         p_sys->b_frame_slice = VLC_FALSE;
 487
 488         if( p_sys->i_picture_structure != 0x03 )
 489         {
 490             p_sys->b_second_field = !p_sys->b_second_field;
 491         }
 492         else
 493         {
 494             p_sys->b_second_field = 0;
 495         }
 496     }
 497
 498     /*
 499      * Check info of current fragment
 500      */
 501     if( p_frag->p_buffer[3] == 0xb8 )
 502     {
 503         /* Group start code */
 504         if( p_sys->p_seq &&
 505             p_sys->i_seq_old > p_sys->i_frame_rate/p_sys->i_frame_rate_base )
 506         {
 507             /* Usefull for mpeg1: repeat sequence header every second */
 508             block_ChainLastAppend( &p_sys->pp_last, block_Duplicate( p_sys->p_seq ) );
 509             if( p_sys->p_ext )
 510             {
 511                 block_ChainLastAppend( &p_sys->pp_last, block_Duplicate( p_sys->p_ext ) );
 512             }
 513
 514             p_sys->i_seq_old = 0;
 515         }
 516     }
 517     else if( p_frag->p_buffer[3] == 0xb3 && p_frag->i_buffer >= 8 )
 518     {
 519         /* Sequence header code */
 520         static const int code_to_frame_rate[16][2] =
 521         {
 522             { 1, 1 },  /* invalid */
 523             { 24000, 1001 }, { 24, 1 }, { 25, 1 },       { 30000, 1001 },
 524             { 30, 1 },       { 50, 1 }, { 60000, 1001 }, { 60, 1 },
 525             /* Unofficial 15fps from Xing*/
 526             { 15, 1001 },
 527             /* Unofficial economy rates from libmpeg3 */
 528             { 5, 1001 }, { 10, 1001 }, { 12, 1001 }, { 15, 1001 },
 529             { 1, 1 },  { 1, 1 }  /* invalid */
 530         };
 531
 532         if( p_sys->p_seq ) block_Release( p_sys->p_seq );
 533         if( p_sys->p_ext ) block_Release( p_sys->p_ext );
 534
 535         p_sys->p_seq = block_Duplicate( p_frag );
 536         p_sys->i_seq_old = 0;
 537         p_sys->p_ext = NULL;
 538
 539         p_dec->fmt_out.video.i_width =
 540             ( p_frag->p_buffer[4] << 4)|(p_frag->p_buffer[5] >> 4 );
 541         p_dec->fmt_out.video.i_height =
 542             ( (p_frag->p_buffer[5]&0x0f) << 8 )|p_frag->p_buffer[6];
 543         p_sys->i_aspect_ratio_info = p_frag->p_buffer[7] >> 4;
 544
 545         /* TODO: MPEG1 aspect ratio */
 546
 547         p_sys->i_frame_rate = code_to_frame_rate[p_frag->p_buffer[7]&0x0f][0];
 548         p_sys->i_frame_rate_base =
 549             code_to_frame_rate[p_frag->p_buffer[7]&0x0f][1];
 550
 551         p_dec->fmt_out.video.i_frame_rate = p_sys->i_frame_rate;
 552         p_dec->fmt_out.video.i_frame_rate_base = p_sys->i_frame_rate_base;
 553
 554         p_sys->b_seq_progressive = VLC_TRUE;
 555         p_sys->b_low_delay = VLC_TRUE;
 556
 557         if ( !p_sys->b_inited )
 558         {
 559             msg_Dbg( p_dec, "size %dx%d fps=%.3f",
 560                  p_dec->fmt_out.video.i_width, p_dec->fmt_out.video.i_height,
 561                  p_sys->i_frame_rate / (float)p_sys->i_frame_rate_base );
 562             p_sys->b_inited = 1;
 563         }
 564     }
 565     else if( p_frag->p_buffer[3] == 0xb5 )
 566     {
 567         int i_type = p_frag->p_buffer[4] >> 4;
 568
 569         /* Extension start code */
 570         if( i_type == 0x01 )
 571         {
 572 #if 0
 573             static const int mpeg2_aspect[16][2] =
 574             {
 575                 {0,1}, {1,1}, {4,3}, {16,9}, {221,100},
 576                 {0,1}, {0,1}, {0,1}, {0,1}, {0,1}, {0,1}, {0,1}, {0,1}, {0,1},
 577                 {0,1}, {0,1}
 578             };
 579 #endif
 580
 581             /* sequence extension */
 582             if( p_sys->p_ext) block_Release( p_sys->p_ext );
 583             p_sys->p_ext = block_Duplicate( p_frag );
 584
 585             if( p_frag->i_buffer >= 10 )
 586             {
 587                 p_sys->b_seq_progressive =
 588                     p_frag->p_buffer[5]&0x08 ? VLC_TRUE : VLC_FALSE;
 589                 p_sys->b_low_delay =
 590                     p_frag->p_buffer[9]&0x80 ? VLC_TRUE : VLC_FALSE;
 591             }
 592
 593             /* Do not set aspect ratio : in case we're transcoding,
 594              * transcode will take our fmt_out as a fmt_in to libmpeg2.
 595              * libmpeg2.c will then believe that the user has requested
 596              * a specific aspect ratio, which she hasn't. Thus in case
 597              * of aspect ratio change, we're screwed. --Meuuh
 598              */
 599 #if 0
 600             p_dec->fmt_out.video.i_aspect =
 601                 mpeg2_aspect[p_sys->i_aspect_ratio_info][0] *
 602                 VOUT_ASPECT_FACTOR /
 603                 mpeg2_aspect[p_sys->i_aspect_ratio_info][1];
 604 #endif
 605
 606         }
 607         else if( i_type == 0x08 )
 608         {
 609             /* picture extension */
 610             p_sys->i_picture_structure = p_frag->p_buffer[6]&0x03;
 611             p_sys->i_top_field_first   = p_frag->p_buffer[7] >> 7;
 612             p_sys->i_repeat_first_field= (p_frag->p_buffer[7]>>1)&0x01;
 613             p_sys->i_progressive_frame = p_frag->p_buffer[8] >> 7;
 614         }
 615     }
 616     else if( p_frag->p_buffer[3] == 0x00 )
 617     {
 618         /* Picture start code */
 619         p_sys->i_seq_old++;
 620
 621         if( p_frag->i_buffer >= 6 )
 622         {
 623             p_sys->i_temporal_ref =
 624                 ( p_frag->p_buffer[4] << 2 )|(p_frag->p_buffer[5] >> 6);
 625             p_sys->i_picture_type = ( p_frag->p_buffer[5] >> 3 ) & 0x03;
 626         }
 627
 628         p_sys->i_dts = p_frag->i_dts;
 629         p_sys->i_pts = p_frag->i_pts;
 630     }
 631     else if( p_frag->p_buffer[3] >= 0x01 && p_frag->p_buffer[3] <= 0xaf )
 632     {
 633         /* Slice start code */
 634         p_sys->b_frame_slice = VLC_TRUE;
 635     }
 636
 637     /* Append the block */
 638     block_ChainLastAppend( &p_sys->pp_last, p_frag );
 639
 640     return p_pic;
 641 }