[mythtv-commits] Ticket #4891: Enabling VBI for a broader array of drivers and hardware

MythTV mythtv at cvs.mythtv.org
Fri Mar 7 23:45:34 UTC 2008


#4891: Enabling VBI for a broader array of drivers and hardware
--------------------------------+-------------------------------------------
 Reporter:  starz909 at yahoo.com  |       Owner:  ijr       
     Type:  defect              |      Status:  new       
 Priority:  minor               |   Milestone:  0.21      
Component:  mythtv              |     Version:  0.21-fixes
 Severity:  low                 |     Mlocked:  0         
--------------------------------+-------------------------------------------
 Hello everyone,

 Currently, the ability to view closed captioning in channels or recordings
 is highly dependent on the drivers for the recording hardware.  With
 software encoders, this isn't a problem because mythtv offers a dialog box
 to specify the location of the vbi device node.  With hardware encoders,
 even the common Hauppauge encoders, mythtv relies on the drivers being
 able to insert vbi data into the mpeg stream, where mythtv will find the
 data and display it, if the user requests it.

 Unfortunately though, few hardware drivers do this well, and some
 developers choose not to add this feature to their driver code.  The
 popular ivtv driver only does this well for some hardware, and, for
 example, a developer of v4l's blackbird driver, Michael Krufky, has
 decided not to implement this feature in the blackbird drivers.

 Why?  Because the driver, and other similar drivers like ivtv, create a
 dedicated vbi device node as well, which gives the computer access to the
 vbi data streaming from the hardware.  In Krufky's and my own opinion,
 this would be a more convenient and stable means of acquiring vbi data for
 broadcasts.

 http://lists.zerezo.com/video4linux/msg20539.html

 If mythtv claims it supports decoding CC, which it must since there are
 menus that allow it to be enabled and configured, then I think it would be
 more efficient for mythtv to give the user the option of specifying where
 the vbi data is to be captured -- the mpeg stream, or a dedicated device
 node.

 I was considering an option that is placed in the mythtv-setup menu, under
 configuring a new hardware encoder card, and when enabled, lets the user
 specify a location for a vbi device node, and perhaps a slider or box to
 input a delay or buffer number if the vbi device node is not synched
 properly with the mpeg node.

 I'm not sure how this external vbi data will be recorded with the video
 nuv file; whether the vbi data should be a separate file linked somehow to
 the video file, either with the same name or through the database, or if
 the vbi data should be inside the nuv file, in which case, I'm not sure if
 a lossless transcoding process will be necessary.

 I consider this a workaround or bug fix, and not a feature request,
 because mythtv is supposed to already decode cc; this is just a means of
 letting it work for a wider range of devices whose drivers do not, and
 perhaps will not support slicing vbi data into their mpeg stream - but do
 provide a functional vbi device node.

 Thank you for your patience and for considering this request,
 Sam

 PS.  Unfortunately, I do not have programming skills sufficient for this
 kind of modification, so I cannot propose a patch, but I am willing to
 help with testing on my free time.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/4891>
MythTV <http://svn.mythtv.org/trac>
MythTV


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