[FFmpeg-user] alternating checkerboard

[Mark Filipak (ffmpeg)]

On 02/09/2021 03:14 AM, Michael Koch wrote:
> Am 09.02.2021 um 04:49 schrieb Mark Filipak (ffmpeg):
>> I don't know the details of the filters that work on pixels ('blend', for example). I hope a 
>> knowledgeable person will respond with suggestions.
>>
>> I'd like to experiment with a filter that mixes pixels from 2 progressive streams on an 
>> alternating checkerboard pattern. Got any suggestions?
>>  _________________    _________________    _________________
>> |# # # # # # # # #   | % % % % % % % %    |#%#%#%#%#%#%#%#%#
>> | # # # # # # # #    |% % % % % % % % %   |%#%#%#%#%#%#%#%#%
>> |# # # # # # # # # + | % % % % % % % %  = |#%#%#%#%#%#%#%#%#
>> | # # # # # # # #    |% % % % % % % % %   |%#%#%#%#%#%#%#%#%
>> |# # # # # # # # #   | % % % % % % % %    |#%#%#%#%#%#%#%#%#
>>
>>
> 
> Have a look at the "maskedmerge" filter. In your case the mergemap file would contain a pattern of 
> 0's and 255's. This file can be generated with "geq" filter (see the example in chapter 2.107).

Thanks for the suggestion. Actually, it appears that the 'blend' filter does what I want, but I'm 
still testing to be sure.
blend=all_expr='if(eq(mod(X,2),mod(Y,2)),TOP,BOTTOM)'
'blend' appears to input 2 frames in 2 streams and output 1 frame (with unknown PTS). 'tblend', on 
the other hand, appears to take 2 frames in 1 stream and output 2 frames, not 1 frame, (again, with 
unknown PTS). It sure would be nice if these filter functions were adequately documented, especially 
regarding how they determine output PTS. But you shouldn't listen to me because, to quote the 
authorities: "That makes no sense".

> Michael
> 
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