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Doesn't HDMI give you the new and wonderful possibility of display lag? (This is particularly pronounced when playing games using iOS devices, especially older
by podperson 14y ago
Doesn't HDMI give you the new and wonderful possibility of display lag? (This is particularly pronounced when playing games using iOS devices, especially older iOS devices, with AirPlay.)
Because the time between a frame being rendered and appearing on screen can increase, you are reacting slowly to events on the device which you perceive as control lag when in fact it's display lag.
- mortenjorck 14y agoCompliant HDMI shouldn't introduce any latency itself. It's just a digital signal, no different in principle than the signal from a wired game controller. Where latency can creep in is a TV's image processing algorithms – a color adjustment algorithm might add a few milliseconds, an edge enhancement might add a few more; a 120hz motion compensation system will add a lot more. Most TVs will allow these to be disabled (often in a specifically labeled "game mode") but a few may inexplicably not allow them all to be disabled, hardwired for a certain degree of latency. AirPlay, on the other hand, introduces a lot of latency because it's compressing the image prior to transport and uncompressing it on the other end. This generally introduces significantly more lag than any TV image processing.
- podperson 14y agoHere's an article on how to detect and measure the effect I'm talking about. http://www.pcworld.com/article/183928/how_to_find_and_fix_input_lag_in_your_HDTV_or_monitor.html http://www.pcworld.com/article/183928/how_to_find_and_fix_in... It's a consequence of using framebuffers in the display device. I mentioed Airport because it exaggerates the effect, but any digital display will likely introduce s little extra lag.
- maxerickson 14y agoI don't think mortenjorck particularly disagrees with you. I think they are reading [HDMI] specifically as [HDMI] rather than [The use of an external display, via HDMI].
- deleted 14y ago[deleted]
- podperson 14y agoSorry I can't reply to you directly, but: EXACTLY. HDMI encodes frames and pipes them to the TV which has to render them. There's no guarantee this will be instantaneous (indeed it's virtually guaranteed that it won't).
- mortenjorck 14y agoIncorrect. HDMI is a standard for transmitting uncompressed video, same as DVI. Raster goes in one end and out the other. AirPlay, on the other hand, does encode frames that need to be uncompressed by a renderer.
- mercury888 14y agonot to mention go through your congested wifi network.
- podperson 14y agoCompressed or uncompressed doesn't matter. The point is that the display device is buffering frames and then rendering them later (ideally imperceptibly later).
- podperson 14y agoCompressed or uncompressed doesn't matter. The point is that the display device is buffering frames and then rendering them later (ideally imperceptibly later). Airplay definitely adds more potential bottlenecks but the principle remains the same.
- brigade 14y agoBut the buffering is not required because of the HDMI link; a display could update each pixel as it receives it over HDMI, just like CRTs did. LCDs buffer at least one frame for many reasons, but "because HDMI requires it" is not among them. And compressed vs. uncompressed does matter, especially when you're talking about video compression. Because compression requires some minimum amount of data before it can even begin to compress, let alone start to send the compressed bitstream over a physical link. And then you have more latency as you add a decode step. Not to mention the complete lack of latency guarantees a wifi link has...
- sp332 14y agoI agree that display lag can be an issue. But HDMI is not the cause. Sluggish post-processing in the TV is (if it does color correction, sharpening, noise filtering, etc. etc.).