Playing HD video to SD decklink in letterbox without cropping


I have a 1920x1080 (16:9) png HD image (test.png). When I do PLAY 1 test.png loop , the image gets cropped on the SD monitor ( 720 x 576) through decklink duo. To operate in letterbox mode ( ie not cropping but black horizontal bars on the top and bottom ), I then thought I should squeeze the image first ( still maintaining 16:9) and decklink hardware on auto cropped ( to 4:3) do the trick. so I did MIXER 1 fill .2 .2 .375 .375 and the image get squeezed. Not sure if the MIXER parameters are right. Is the procedure correct. Any thought.


What is your goal ?

a 4:3 SD output where HD content is letterboxed.
or a
16:9 SD (anamorphic) output?


@maurice78: I need to know how to generate the output in both cases, but without cropping on the decklink output. Also I can’t come up with an general formula for other resolutions like 2G, 3G too. Any thought? Will the AMCP mixer command percolate to the decklink consumer and the desire affect will be visible on the final output.


there are different ways to get there and it all depends
on your main content type what works the best (needs the lowest amount of commands ;))
if you have lot’s of HD content to show on a SD channel the workflow will differ against a workflow where all your content is SD and some HD content will come along;

I guess the easiest way is make a HDchannel in caspar and choose in the black magic software what your output needs to be in SD. See page 25 in


then 4:3 content needs
MIXER 1-10 FILL 0.125 0 0.75 1


@Maurice78: In my workflow, the contents are mainly in HD (mxf) but still it should support few of the old SD(4:3) content as well. In fact i want a universal solution : 16:9 anamorphic o/p through sd decklink and full HD through hd decklink card.


Ok then life is easy :wink:
make a HD channel and a PAL (or NTSC) channel in caspar
HD channel on one decklink card SD channel on the other
and route ch1 to ch2 with
PLAY 2-10 route://1

and put a mixer command on channel 2 when the content is 4:3


@Maurice78: Thanks for the great feedbacks. But still i want to confirm if a HD video can be routed to SD decklink card without cropping. I want the command to work after swapping the SD with the HD card. Will your mixer command work here?


Yes without cropping
mixer command i’m not fully sure about
i guess some figure’s change due too the rectanglar pixels in SD
but it should be 4:3ish now with this command.
i am not behind a machine now to test this for you.


@Maurice78: I think i got more than i bargained for, but if you get time please test both the cases, since i don’t have a HD card. Hoped this thread helps some developer. Thanks.