Changeset 1046

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Timestamp:
2005-03-04 23:54:50 (4 years ago)
Author:
silvia
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Small update. :)

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  • standards/draft-pfeiffer-annodex-02-rc2.txt

    r1044 r1046  
    9569565.  Handling time in Annodex format bitstream 
    957957 
     958   With time-continuous data like Annodex, one needs to handle data at 
     959   four different levels: 
     960   o  at the bytes level, upon seeking. 
     961   o  at the packets level, upon encapsulating. 
     962   o  at the granules level, upon recompositing. 
     963   o  at the time level, upon displaying and addressing. 
     964   This section explains how they all fit together. 
     965 
    9589665.1  Conceptual overview 
    959967 
    …… 
    9941002                    audio bitstream 2 
    9951003                           ------------------------------- 
     1004 
     1005 
     1006 
     1007Pfeiffer, et al.       Expires September 3, 2005               [Page 18] 
     1008  
     1009Internet-Draft                  ANNODEX                       March 2005 
     1010 
     1011 
    9961012                           |     |/////|     |     |     | 
    9971013                           ------------------------------- 
    …… 
    10021018   associated with the granule position of 0 on all logical bitstreams. 
    10031019   Typically, a newly created Annodex file starts all its logical 
    1004  
    1005  
    1006  
    1007 Pfeiffer, et al.       Expires September 3, 2005               [Page 18] 
    1008   
    1009 Internet-Draft                  ANNODEX                       March 2005 
    1010  
    1011  
    10121020   bitstreams at granule position 0, and a typical extract of an Annodex 
    10131021   bitstream, such as the one starting at t_url in the image above, 
    …… 
    10501058   secondary header packets for each logical bitstream. 
    10511059 
     1060 
     1061 
     1062 
     1063Pfeiffer, et al.       Expires September 3, 2005               [Page 19] 
     1064  
     1065Internet-Draft                  ANNODEX                       March 2005 
     1066 
     1067 
    10521068   Each one of the bitstreams insert data into the Ogg bitstream through 
    10531069   packets which have an associated temporal duration based on the 
    …… 
    10581074 
    10591075   The granule position together with the granulerate and granuleshift 
    1060  
    1061  
    1062  
    1063 Pfeiffer, et al.       Expires September 3, 2005               [Page 19] 
    1064   
    1065 Internet-Draft                  ANNODEX                       March 2005 
    1066  
    1067  
    10681076   information of the skeleton secondary header packets for the 
    10691077   particular logical bitstream are used for the calculation of the time 
    …… 
    11071115   t_page = basetime + ((keyindex + keyoffset) / granulerate) 
    11081116 
     1117 
     1118 
     1119Pfeiffer, et al.       Expires September 3, 2005               [Page 20] 
     1120  
     1121Internet-Draft                  ANNODEX                       March 2005 
     1122 
     1123 
    11091124   The basetime provides the time offset used at the beginning of the 
    11101125   logical bitstream for the first data packet and thus MUST be added 
    …… 
    11141129   44100 (i.e.  44100 samples per 1 sec), a granuleshift of 0, and 
    11151130   starts at 4 sec.  When reaching a granule_position of 88200, this 
    1116  
    1117  
    1118  
    1119 Pfeiffer, et al.       Expires September 3, 2005               [Page 20] 
    1120   
    1121 Internet-Draft                  ANNODEX                       March 2005 
    1122  
    1123  
    11241131   maps to a time position of 6 seconds: 
    11251132 
    …… 
    11631170 
    11641171   A note about field overflows: an overflow of the granule position 
     1172 
     1173 
     1174 
     1175Pfeiffer, et al.       Expires September 3, 2005               [Page 21] 
     1176  
     1177Internet-Draft                  ANNODEX                       March 2005 
     1178 
     1179 
    11651180   field can destroy the temporal integrity of the Annodex physical 
    11661181   bitstream.  In this case, a multiplexer MUST end the Annodex physical 
    …… 
    11701185   overflow of the page_sequence_number on one of the logical 
    11711186   bitstreams. 
    1172  
    1173  
    1174  
    1175 Pfeiffer, et al.       Expires September 3, 2005               [Page 21] 
    1176   
    1177 Internet-Draft                  ANNODEX                       March 2005 
    1178  
    11791187 
    118011885.3  Addressing/seeking into the bitstream 
    …… 
    12181226 
    12191227   Therefore, once seeking has located the correct Byte position that 
     1228 
     1229 
     1230 
     1231Pfeiffer, et al.       Expires September 3, 2005               [Page 22] 
     1232  
     1233Internet-Draft                  ANNODEX                       March 2005 
     1234 
     1235 
    12201236   refers to the given temporal offset, it MUST seek back.  For logical 
    12211237   bitstreams that have a non-zero "granuleshift" in the skeleton, it 
    …… 
    12251241   position that satisfies all these requirements is the correct seek 
    12261242   position. 
    1227  
    1228  
    1229  
    1230  
    1231 Pfeiffer, et al.       Expires September 3, 2005               [Page 22] 
    1232   
    1233 Internet-Draft                  ANNODEX                       March 2005 
    1234  
    12351243 
    12361244   A player that presents from an offset MUST take into account that the 
    …… 
    12701278   This is important also to allow caching of such files as is required 
    12711279   for Web proxies and described in temporal URI addressing [16]. 
    1272  
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    12801280 
    12811281