[mythtv-commits] Ticket #2903: Patch to fix refresh rate calculation for interlaced modelines, allows Bobdeint on 50Hz displays

[MythTV]

#2903: Patch to fix refresh rate calculation for interlaced modelines, allows
Bobdeint on 50Hz displays
----------------------------------+-----------------------------------------
 Reporter:  drvik at bigpond.net.au  |        Owner:  ijr    
     Type:  patch                 |       Status:  new    
 Priority:  minor                 |    Milestone:  unknown
Component:  mythtv                |      Version:  0.20   
 Severity:  medium                |   Resolution:         
  Mlocked:  0                     |  
----------------------------------+-----------------------------------------
Changes (by anonymous):

  * status:  closed => new
  * resolution:  invalid =>


Comment:

 Replying to [comment:1 danielk]:
 > Incorrect, a 50Hz interlaced display only has a 25Hz frame rate.

 This is true, but irrelevant. Interlacing is simply a way of space-time
 subsampling the normal progressive picture. Pairs of fields tend to get
 treated as one frame when discussing broadcast standards or when digitally
 encoded, but this pairing is entirely artificial for true interlaced
 video.

 > You also don't want to use bob-deint with an interlaced display,
 > use kernel or linear blend when there is a resolution missmatch and no
 > deinterlacing when the source and destination line count matches.

 When you have interlaced content and an interlaced display, one solution
 is for the display to show each field independently. If there is a
 resolution mismatch, this can be accomplished with a bob (which is needed
 to compensate for the different size of the vertical offset between
 fields) and rescale to the output resolution. It is true that only half of
 the lines need to be computed for each output field, but with hardware
 scaling it's not worth the effort.

 In fact, I can't think of a good reason (aside from the possible need for
 vertical filtering to avoid flickering) why a 50Hz interlaced display
 should be treated differently than a 50Hz progressive display by MythTV.

 Actually, after reading my last paragraph, I realized that some of the
 more sophisticated deinterlacers like yadif could give better results than
 bob, but there is still a good reason to output at the full field rate,
 rather than be restricted to half the field rate.

 > See mythtv-vid branch for configuring such a setup.

 I actually don't have an interlaced display, but after reading a forum
 post with a link here stating that many people use bob deinterlacing with
 the above patch, I felt compelled to respond.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/2903#comment:2>
MythTV <http://www.mythtv.org/>
MythTV