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I'll try to ask my question in a generic way (without mentioning specific models and brands):

Assume the maximum resolution a graphics card supports is X*Y (e.g. less than 4K). When I try to play a video with a higher resolution (e.g. a 4K video), it's barely running (it's mostly hanging).

Does this mean that the graphics card did not participate in playing the video (because it's in a higher resolution than it supports), or that nevertheless it tried to assist in playing the video but managed poorly (because it's in a higher resolution than it supports)?

(Or maybe it's something completely else and I'm missing how graphic cards work or what the 'maximum resolution supported' means.)

Thanks in advance.

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Take a look at the CPU usage. That's your answer right there. ;) – Daniel B Jul 13 '14 at 1:35

Almost every part of your system participates in the decoding and presentation of video files, and any one of them could be a bottleneck.

One attribute of a video is its Mbps value - this is effectively the amount of data that needs to be processed in a second to display the video. A 4K video could have any Mbps value, but lets say 15Mbps for the sake of this discussion.

So everything in the path will attempt to meet this data speed requirement. The first step is lifting the data off whatever storage device it is on. In the majority of cases, this is fine, internet and local disks will manage this without issue.

Next it must be transmitted to the machine that will process the video. If the video is sourced from local storage, then again, generally no problem. However, if it is coming from the internet, then the quality of the service comes into play. An ADSL service may struggle with 15Mbps throughput (despite the theoretical max of 24Mbps).

Then the video is processed, and CPU comes into play, as well as memory speed. Decoding the video may include the participation of the GPU if it has drivers that support the codec being used. Otherwise the CPU must take the load, and this may be a bottleneck.

The final step is displaying the video on screen, which at less than 4K resolution is trivial for a modern GPU.

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