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  1. Member
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    Dec 2019
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    Both the UleFone Armor 2 and the Samsung Galaxy S7/S7 Edge have the same GPU: a Mali T880.

    When playing the exact same 2160p@30fps and 1080p@120fps video files, the Galaxy S7 Edge plays it smoothly, without any frame skipping or lagging.

    The UleFone Armor 2 however:
    • Native media player: plays it with stuttering and frame skipping (but smooth audio).
    • VLC for Android (with enforced hardware acceleration): Video freezes after first frame, while the audio keeps playing.

    But the Armor 2 plays 1440p@30fps perfectly smoothly.
    Side note: The S7 Edge however even plays 2160p@60fps footage smoothly, a framerate it can't even record at at 2160p (because decoding obviously needs less computing power than encoding).

    Obviously, these devices have different CPU's (Exynos 8890/Snapdragon 820 vs. Helio P25), but isn't the GPU mainly responsible for video playback (and recording)?

    If both devices are equipped with the exact same GPU, how come only the S7 plays the 2160p videos smoothly? Shouln't both devices play it identically?

    (Storage speed is certainly not the reason, because even storage speeds of early-2010s's phones are by far faster than the bitrates of those sample videos.)

  2. Member
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    Originally Posted by jagabo View Post
    Originally Posted by LG7 View Post
    I am wondering how 1080p@120fps plays smoothly but 2160p@30fps not, despite both have the exact same pixel rate of [strike]299792458[/strike] edit: 248832000 pixels per second (3840216030 and 19201080120).
    With CPU decoding this could be an issue of cache size. Once the working set size (1 frame of memory*) exceeds the L3 cache size memory access becomes much more expensive. A seven year old computer probably has a cache size of 6 MB -- that's large enough to hold one frame of 1920x1080 YUY2 video (~4 MB). But not large enough to hold one frame of 3840x2160 YUY2 video (~16 MB). So even though the total throughput of the two is the same the latter exceeds the size of the L3 cache, resulting in cache thrashing.

    * With modern codecs the working set while decompressing video is typically several frames. But the issues still holds -- the 4x larger working size is going to result in less effective caching.

    Could it be a related reason here too?

  3. I'm a Super Moderator johns0's Avatar
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    LG7-Please do not open another thread on the same subject,continue here,This thread is closed.
    I think,therefore i am a hamster.

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