Hi, not 100% sure what exactly you mean with "(in HD and 1000fps)", as some people use the Term "HD" on its own while meaning Standard HD /HD ready 1280x720p HD or 720pHD, and 1920x1080 is almost exclusively referred to as "FullHD" usually, but depending on context "HD" could also be FullHD Resolution.
https://en.wikipedia.org/wiki/720p So for now i will just assume you probably meant 1920x1080p 1000fps, as its the Highest Framerate @ Highest Resolution the Camera can Output, while still also trying to answer the Same Question if you meant 1280x720p 1000fps, as that would also have a legit advantage over actual Full HD in your specific usecase.
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The 2.1 with 32Gb Memory can hold 11,0368s worth of real time footage at 1920x1080p 1000fps and 24,8410s worth of real time Footage at 1280x720p 1000p.
Save time to SD Card is about 1m20s for 2000frames (2 seconds at 1000 frames per Second = 2000 Frames) at 1920x1080p in H.264 with Maximum Bitrate (60Mbps), and only very slightly faster in 1280x720p (like 1m10s or 1m15s) from a quick test i just did (sample size 1 for each, so your results might be different...).
External SSD will be a bit faster, but in reality also just marginally, meaning you might shave off 10 or so seconds, 20 at best, if i had to guess. SSD to SD Card Save Speeds are a lot different for DNG Footage, but for H.264 not all that much.
External SSD will be the Fastest for this, Transfer via Ethernet should be quite a bit slower i assume, but i have no real experience on this, never actually tried that and compared speeds on that.
HDMI will only output a real time Video Feed from the Sensor @ 60fps when recording, and in Playback mode also just a 60 fps Feed off your Slowed Footage at whatever Speed you play it back, or freeze Frame, depending on what the Internal Monitor shows. so also not really suited to extract footage, and if you do, A LOT SLOWER than about any other method (probably still faster than Saving in DNG, but whats the Point in doing that).
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Given that you will need the Majority of your 5 Minute Time Frame, if you tried to save your 2s Clips individually, you probably are able to get 5 clips Recorded that way.
Record the First one Right away, save, immediately record the next one, save, etc.
You would probably want to set up some kind of Script for that, to save time, because else you almost sure will only be able to get like 2 to 4 in that time Frame that way, because of setting Save start and end Points and all that.
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Best way to do that would in my opinion be to use the Segmented Recording Mode, which would allow you to split your 32GB into Segments of exactly 2 Seconds each, which would give you 5 and a Half Clips of that Length in that Time Frame (assuming 1920x1080p), or 6 Clips, if your "2 Second" Clip Length isnt meant as exactly 2.00Seconds as in exactly 2000 frames, and could be 1,833s for each clip.
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Lowering your Resolution (720pHD still looks good enough and still provides Plenty of detail, and is also 16:9, so can be easily used with other 16:9 Aspect Ratio Footage, if you need to maximize the Amount of clips. if you need FullHD Resolution for some Reason, like selling the Clips or something is obviously a different story...) to 1280x720p would allow you to record 13 clips of 1,91s Length each in Segmented recording mode on a 32GB 2.1, so unless you absolutely need the Resolution for some Reason, and your main objective here is only to maximize the number of individual clips recorded within a 5 Min Timeframe at any cost, consider lowering the Resolution as much as practical for your application.
1024x576p at 1000fps would already give you 38,814s of record time, meaning 20 clips of 1,94s Length each, fyi.
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So if i was in your situation, i would look into segmented Recording, no matter what kind of resolution you end up going with. No matter how hard you tried, you most likely wont be able to record more than that what will fit into 32GB RAM anyways, if it has to be also saved within 5 Minutes, so why even try. On 720pHD you are probably even at a huge advantage compared to Straight up saving, when just filling up your RAM, and Saving later.
