[mythtv-commits] Ticket #7861: Closed captions become "stuck"

MythTV mythtv at cvs.mythtv.org
Tue Jan 5 00:03:51 UTC 2010


#7861: Closed captions become "stuck"
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 Reporter:  Jim Stichnoth <stichnot@…>          |       Owner:  janne  
     Type:  patch                               |      Status:  new    
 Priority:  minor                               |   Milestone:  unknown
Component:  MythTV - Video Playback             |     Version:  unknown
 Severity:  medium                              |     Mlocked:  0      
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 Occasionally, the timecode for a closed caption is corrupt and is treated
 as a very large number, corresponding to a timecode far in the future.
 When this is encountered during playback, subsequent closed captions are
 blocked until a seek operation clears the caption buffer.  The result is
 that the previous caption appears to be stuck (if the offending caption is
 a "clear" operation), or that no subsequent captions are displayed.

 I have encountered this problem in ATSC broadcasts using the HDHR.  More
 commonly, lossless transcodes of ATSC/HDHR recordings seem to sometimes
 corrupt some caption timecodes, though unfortunately I haven't been able
 to track down the source of the corruption in mythtranscode.

 When a new caption is written to the buffer, this patch tries to guess
 whether the reader appears to be stuck waiting on a caption whose
 timestamp is too large.  It does this by checking whether it is writing a
 timestamp that is smaller than the timestamp being waited on but larger
 than the previously read timestamp.  For example, if the sequence of
 timestamps is 1000, 9999999, 2000, and the reader is waiting on 9999999,
 then the write of 2000 (which is between 1000 and 9999999) will deduce
 that the reader is stuck.  When this happens, the timestamp that the
 reader is waiting on is reset to a value reasonably close to the
 previously read timestamp, so that it becomes unstuck.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/7861>
MythTV <http://www.mythtv.org/>
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