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Video color space format and lag?
Posted: 14 Jun 2018, 03:59
by silikone
Is it possible that the color format used to transfer a video signal can be a source of input lag? The reason I ask is that the common 4:2:0 subsampling format used for videos is more often than not stored in a planar format, which if sent over a cable serially, would not be able to deliver results to the screen instantly.
Re: Video color space format and lag?
Posted: 15 Jun 2018, 19:00
by Chief Blur Buster
Only if the horizontal scanrate goes up. The horizontal scanrate is the number of pixel rows per second transmitted. 67KHz means a single row of pixels is transmitted in 1/67000sec (excluding transceiver delays at both ends).
So that means switching 4:4:4 vs 4:2:2 vs 4:2:0 makes no difference in input lag.
But switching to lower chroma resolution can enable a higher refresh rate (more bandwidth available to go higher Hz).
Which does mean less lag.
Over ten years ago, my old Samsung 245BW monitor could overclock to 75Hz but it switched to 4:2:0 when it did that.
Today, monitors like the Predator X27 monitor can only do HDR at 144Hz if you go less than 4:4:4 chroma.
The refresh rate is the bigger determinant of the scanout-related input lag. (Unless HDMI 2.1's new Quick Frame Transport techniques are used -- that's essentially a Large Vertical Total -- a higher scanrate. A large VBI with a faster active-image scanout)