Why is that? The specs said it can read 80mb/s and write 50mb/s. It is over kill for recording 4k video? Or the ultra do just fine. I know I can't record 4k now but this phone is capable once we unlock the feature right?
Sent from my C6903 using xda app-developers app
It depends on the bitrate of the video (compression) recorded as well as the max write speed of the device.
While you are right about 4k video needing more bandwidth, it's not as bad as you think. If you look at
this article about streaming 4k video I think it is unlikely that a mobile device will go over 20 Mbit/s for 4k video. That means a write speed of 1.25 mb/s is sufficient (with a little overhead, 2 mb/s would suffice).
Even if we take the worst case, the Bluray 1080p rate (which is at most 40 Mbit/s) multiplied by 4 for the 4K resolution, you still get a bitrate of 160 Mbit/s which is equals 20mb/s.
A write speed 50 mb/s is over-kill for anything other than a professional DSLR (for bursts of raw photo's), or a camera that records uncompressed video (like a Canon 1Dc or Epic RED). But even for a lot of those devices, the write speed is overkill because of hardware limitations. For example, the cardcontroller in my DSLR (a Pentax K-5) is "only" capable of writing at 30 mb/s, so anything over that is just a waste anyway.
Think of it this way: at 50 mb/s your 64 Gb card would be full after 21 minutes of recording, which I think is unlikely for a cellphone.
Hope this helps you save some money
