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Difference Between Playback Card and Video Card

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Daniel Skrobowski
Difference Between Playback Card and Video Card
on Jul 25, 2014 at 5:26:54 pm

Hello, I've been trying to figure out something to no avail.

Could someone please explain the difference(s) in function between between the "playback" function of capture/playback devices like the UltraStudio and Decklink products and GPUs?

I'm a little confused about the "playback" function of capture/playback devices and how it differs from the rendering/playback capabilities of a GPU. Blackmagic Design states concerning the Decklink product line, "Because DeckLink captures and plays back DPX, DVI and QuickTime files you can use your favorite VFX software such as After Effects® CC, Nuke, Photoshop® CC and more." And, "DeckLink is the highest quality editing solution for Adobe® Premiere Pro® CC with full support for the Mercury Playback engine for massive range of RT effects." And, "DeckLink works with After Effects® CC, Nuke, Photoshop® CC and Smoke."

I thought that playback was what a GPU was for, especially for products like Premiere Pro, Media Composer, and After Effects.

Could someone please explain the differences in function between the "playback" function of a capture/playback card and a GPU? What can a "playback..." card do that a GPU can't, and vice-versa? Please feel free to include specifics and include as much information as need be.

All tips are appreciated.

Thanks.


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Chad Pearson
Re: Difference Between Playback Card and Video Card
on Jul 25, 2014 at 8:04:54 pm

The simplified answer is a "playback" card has no GPU and therefore no way to generate (composite) or process the frames of video as they are sent to the output. In other words it only accepts fully pre-rendered frames.

GPU's on the other hand take multiple pieces of graphics, like bitmaps or vector based instructions (ie draw a line from point X to point Y) and composite it all together into a video frame to be sent to its output. Even just playing back a video in a window on your computer requires the video to be "shrunk" and inserted into a box with a menu and a close button. That processing is not done by the operating system, but by the GPU.


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Daniel Skrobowski
Re: Difference Between Playback Card and Video Card
on Jul 27, 2014 at 2:15:34 pm
Last Edited By Daniel Skrobowski on Jul 27, 2014 at 2:18:15 pm

Thanks for your reply, Chad.

If a playback card can only "accept prerendered frames," how can it be used in something like After Effects? Where are the advantages of using a playback card for playback instead of using a GPU for playback? If I've got a high-end GPU and a playback card in my workstation, which device do I plug my main monitor into?


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Chad Pearson
Re: Difference Between Playback Card and Video Card
on Jul 28, 2014 at 7:29:03 pm

Video editing software like After Effects process the video internally, (or using the GPU on the other graphics card) and then send the final rendered frames to the playback card. The reason to use a separate playback card is either

A) you are already using both the outputs on your main graphics card (for your editor and/or other things)

B) you need to output in SDI, component or another broadcast signal (computer graphics card typically only support VGA/DVI/Displayport)

C) You need the audio embedded directly in the video signal and not played separately through your PC speakers (playing separately can cause lip sync issues since the audio/video signals are going out different paths from the computer to your monitor/speakers).


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