[mythtv-commits] Ticket #10273: CEA-708 captions are delayed because of incorrect byte-pair handling

MythTV noreply at mythtv.org
Sun Jan 22 02:51:58 UTC 2012


#10273: CEA-708 captions are delayed because of incorrect byte-pair handling
----------------------------------+-------------------------
     Reporter:  argilo@…          |      Owner:  danielk
         Type:  Patch - Bug Fix   |     Status:  new
     Priority:  minor             |  Milestone:  unknown
    Component:  MythTV - ATSC     |    Version:  Master Head
     Severity:  medium            |   Keywords:  cea-708
Ticket locked:  0                 |
----------------------------------+-------------------------
 ATSC closed captions (CEA-708) are sometimes delayed due do a bug in the
 way the DTVCC transport layer is packetized.  According to the CEA-708
 specification:

 "The end of the packet is indicated by either: (1) receipt of the header
 (cc_valid = 1, cc_type = 11) of the next DTVCC packet, or (2) receipt of a
 byte-pair where cc_valid = 0 and cc_type = 10 or cc_type = 11."

 But only case (1) is handled currently.  As a result, a received packet
 will not be processed until the next one arrives, which in some cases only
 occurs after a long time has passed.  This usually manifests in roll-up
 captions that are missing the last letter or two until more text appears,
 on in pop-on captions that appear too late, not leaving enough time for
 the viewer to read them before they disappear.

 The attached patch adds handling for case (2).  I have tested it with the
 PBS test material (http://ncamftp.wgbh.org/DTV/CEA%20test%20material/) and
 recorded programs from various local ATSC stations.  The delays are gone,
 and I have not observed any new problems.

-- 
Ticket URL: <http://code.mythtv.org/trac/ticket/10273>
MythTV <http://code.mythtv.org/trac>
MythTV Media Center


More information about the mythtv-commits mailing list