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My wife bought a GoPro Hero3 for some simple home video: kids, holidays, etc.
The problem is that some videos are not playing very well on our old PCs. We want to buy a new one for video editing. As far as I understood, such a computer should have as strong of a CPU as possible and plenty of RAM. It seems that the video card also has some role, but it's not as important as CPU/RAM in general. Is this assumption correct?
Dealing with HD video has two main components. The first is the ability to decode the highly compressed video (which is computationally intensive) and then is the ability to deal with the large uncompressed data (which is bandwidth intensive).
The fastest encoders/decoders use the GPU on the graphics card to improve performance as a GPU is far more capable at attacking the problems related to rendering and compression than a traditional CPU is. So if you have one of these, then the GPU is by far the most important piece. If you don't however, then the CPU becomes by far the most important piece as encoding/decoding on a CPU is very, very intensive.
As far as dealing with the uncompressed data, the relatively small compressed files will be decompressed into memory and then played out of memory, so it is important to have high speed RAM, but not necessarily the need for a lot of it for play back. For editing on the other hand, quantity becomes a bigger factor since the more video that can be stored in memory, the smoother your editing experience will be.
Finally, you have the hard drives. It is very helpful if these are quick for loading videos (particularly for editing) and also for working as scratch disk (where editing stores temporary files that don't fit in memory), however it is probably the least critical part. This can change though if you start working with higher quality, less compressed video where the file sizes start getting larger.
So, to summarize, GPU is highest priority if your software can use it, otherwise CPU and then speed of memory, quantity of memory and speed of hard drive in that order. CPU is still second most important if you do have GPU processing support. If you don't, then GPU is of almost no importance at all.
As you mentioned, there are three important components; ram, CPU, and GPU. Another component worth considering is the hard drive.
RAM isn't incredibly important unless you intend to be doing intense visual effects. In my opinion, 8 gigs is the sweet spot for cost right now. If you want to do effects with something like After Effects, Smoke, or Nuke, 16 gigs is the sweet spot. Video editing is largely a linear task so ram isn't as important as in other high performance tasks.
The CPU is very important, but the requirements are very different from something like gaming. Video rendering uses essentially as many cores are available, so an 8 core i7 with a low clock speed would outperform a super speedy dual-core i5. I would recommend either a quad or octo-core Core i7 or, if you have the budget, a Xeon.
The GPU is by far the most critical component, but only if your software can take advantage of it. I always recommend Nvidia because most professional programs use CUDA which is exclusive to Nvidia GPUs. Usually your best option is a GeForce GTX, I would recommend the 660 or 760. At a higher price range you have something like the Titan Z or the GTX 970. Quadros aren't worth the cost for personal use because reliability and uptime isn't a major issue.
In addition to the three previously mentioned components, I would also recommend a 512 gig Intel SSD. They will significantly increase the speed of your computer, especially when rendering. I have seen dozens of articles listing SSDs as the most cost-effective upgrade for a computer.
Another thing worth mentioning is that if you're looking to buy a machine out of the box, look for something marketed as a workstation. Those will have the specs that you need. The personal favorite manufacturers are Dell, HP, or Apple.
I'm using a GoPro Hero 3+ too
Even on my fast MacPro Westmere (mid-2012) setting your GoPro to resolutions above 1440 will slow playback and rendering. Going up to 2K and 4K might not even work at all.
Also, if using the ProTune setting on your GoPro, make sure you utilise the free GoPro Studio conversion tool to get vastly improved picture quality from the native MP4 files GoPro creates; otherwise the videos can look a bit flat.
Hope this helps
For playing and editing video I'd suggest the following criteria are the most important:
For particular needs you may vary this, but it's a pretty good list.
I have an old iMac that suffers badly with GoPro footage. I borrowed my wife's rMBP that has an i7 CPU, 16GB RAM, SSD, and a card reader.
This machine imported in an instant! Converting protune still took a little time, perhaps faster than 1:1 (meaning 10 minutes of footage was converted faster than 10 minutes) but you'll want to go eat a snack if you are working with an afternoon of GoPro footage. Editing (iMovie) was smooth and easy. No lag or stuttering at all. Exporting (rendering) was pretty quick. No snack needed.
The hardware accleration of the i7 was amazing. The rig I build will have the fastest i7 they make!! RAM is good but 16-32 should do it. SSD is expensive but essential!! A decent GPU is enough.
