user11607: I am trying to build cheap recording and instant replay system using two or three GoPro4 cameras. The idea is that I can put cameras on stands, connect them with computer and record two or three different scenes at the same time at 720p, 120fps. Is this possible with wifi connection to receive 2 or 3 signals from GoPros and record them simultaneously to a computer? 
The next thing I need is the ability to rewind certain scene/camera recording (while still recording in the background) and just preview instant replay of a specific time frame or maybe even frame by frame.
Is this possible? Can someone point me in the right direction for some kind of software or additional hardware I would need in order to accomplish this?

user10931: I believe the answer is no, no, and no, for several reasons.
First off, GoPro don't support their cameras as broadcast cameras.  They are person video recording devices.  I tried using the HDMI output of a Hero3+ camera to feed into a studio broadcast system, and when it didn't work the response was "it's not supposed to".  The Hero3+ (and I presume the Hero4) do have ways of sending video over wifi so that you can get a vague idea of what the camera sees, but it's nothing like full resolution.  So the first "no" is that you cannot really extract good video from the GoPro in real-time.  You have to record it and them dump the card.
The second "no" is that 120fps is just barely starting to be supported at the video transport layer.  Yes, people have been talking about gaming consoles that can achieve 120+ fps for some time, but actually driving that kind of speed to a monitor?  Very hard.  And impossible with the HDMI output of the Hero4, which is limited to 60p: https://gopro.com/support/articles/hero4-hdmi-output-information
The third "no" is getting that 120fps input into your computer.  There is screen recording software that can scrape 120fps output from your GPU, but recording 120fps of 720p (or greater) is still a very specialized thing that's outside your "cheap recording and instant replay system" parameters.  There are video capture cards that claim 120fps recording, but they are cheating: they are multiplexing 4 SD signals (thus really recording 4x 30 fps and calling it 1x 120 fps).

11607: <p>I am trying to build cheap recording and instant replay system using two or three GoPro4 cameras. The idea is that I can put cameras on stands, connect them with computer and record two or three different scenes at the same time at 720p, 120fps. Is this possible with wifi connection to receive 2 or 3 signals from GoPros and record them simultaneously to a computer? </p>

<p>The next thing I need is the ability to rewind certain scene/camera recording (while still recording in the background) and just preview instant replay of a specific time frame or maybe even frame by frame.</p>

<p>Is this possible? Can someone point me in the right direction for some kind of software or additional hardware I would need in order to accomplish this?</p>
 10931: <p>I believe the answer is no, no, and no, for several reasons.</p>

<p>First off, GoPro don't support their cameras as broadcast cameras.  They are person video recording devices.  I tried using the HDMI output of a Hero3+ camera to feed into a studio broadcast system, and when it didn't work the response was "it's not supposed to".  The Hero3+ (and I presume the Hero4) do have ways of sending video over wifi so that you can get a vague idea of what the camera sees, but it's nothing like full resolution.  So the first "no" is that you cannot really extract good video from the GoPro in real-time.  You have to record it and them dump the card.</p>

<p>The second "no" is that 120fps is just barely starting to be supported at the video transport layer.  Yes, people have been talking about gaming consoles that can achieve 120+ fps for some time, but actually driving that kind of speed to a monitor?  Very hard.  And impossible with the HDMI output of the Hero4, which is limited to 60p: <a href="https://gopro.com/support/articles/hero4-hdmi-output-information" rel="nofollow">https://gopro.com/support/articles/hero4-hdmi-output-information</a></p>

<p>The third "no" is getting that 120fps input into your computer.  There is screen recording software that can scrape 120fps output from your GPU, but recording 120fps of 720p (or greater) is still a very specialized thing that's outside your "cheap recording and instant replay system" parameters.  There are video capture cards that claim 120fps recording, but they are cheating: they are multiplexing 4 SD signals (thus really recording 4x 30 fps and calling it 1x 120 fps).</p>
