FS700 where is my full buffer?

G

Geesbert

Member
whatever I try, i seem to be able to record only 5 sec in 240fps.

class 10 card, 95mb/s, tried different cards, end trigger, start trigger, whatever...

shouldn't that be 8 sec?



Stefan
 
I would say yes, and the resulting clip is 64 seconds when in the 30P mode.
 
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I found the solution to my problem: it seems that the hdmi out eats the buffer. with a zacuto evf or a dp6 recording time ist reduced by one second, with a large Hdmi screen it can be halved. will sdi do the same thing?
 
I conducted a test on this. first, I connected my DP6 via HDMI, recording at 240fps- got 12 seconds in buffer.
then, I tried via HDSDI- got 9 seconds. then, I tried with no external monitor connected- got 9 seconds. then I reconnected the monitor via HDMI- got 10 seconds. tried this all with a stopwatch- did my best to nail the times. seems to me the "8 second" buffer is highly variable. really weird. I'll do some more testing...
 
I had shot for two days over the weekend shooting a ton of 240fps clips. All of the 240@24p resulted in 80-second clips, which is 8 seconds in real time. I also had a Zacuto EVF connected the whole time.
 
yes, the resulting clips are all 80 seconds (actually, Windows reports them as 1:19) but the buffer (i.e. time that the tally is lit) does in fact vary a bit... not the same issue as the OP, but interesting nonetheless.
 
Well, this is intriguing, so I ran some tests... I filmed the Digital Slate app (Android) so I could see how much real time I was capturing. I don't think the record or activity LEDs are much use as a reference, as they are more about the time the camera spends processing / saving data.

All tests were filmed at 240 FPS into a 24 FPS clip. All on a Lexar Pro 64GB class 10 card.
  • Film of a phone (tiny in frame, very little movement overall) running the app, no EVF -- captured 7.9 seconds, clip length 79 seconds.
  • Phone plus a tablet playing a movie to create more motion, no EVF -- captured 7.9 seconds, clip length 79 seconds.
  • Phone only, with EVF (SmallHD DP4 on HDMI) -- captured 7.9 seconds, clip length 79 seconds.

Seems really consistent to me! Bear in mind that with end trigger, you need to leave it running after going into Super Slow mode, to fill the buffer -- otherwise you will certainly get a short clip.

The only issue I saw was that the numbers on the Digital Slate counter were advancing really unevenly on playback -- but I guessed that was the app combined with the phone's display refresh rate. Filmed a swinging pendulum (good smooth motion reference) to confirm it -- the camera captures motion smoothly.

It took about 30 seconds (maybe a little more) for the camera to save each clip, which didn't seem bad at all -- certainly a class 10 card will help here. However I doubt a slower card would affect the capture time, since at that point the camera is only saving to onboard RAM, as I understand it.
 
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Have you looked at the file sizes of each take? The Camera shoots at a variable AVCHD rate, and it could be that the buffer is filling up more quickly on more complicated shots.

For example, a high ISO would have a lot of noise, and therefore use more bitrate per frame, than the same shot at ISO 100 (exposed the same).
 
That's why I made one test with very little motion (just a phone with a timecode, very small in the frame) and another test with lots of motion (phone plus a tablet playing a movie). Both clips were exactly the same length. (I didn't check the file sizes.)

I'd expect this as the data going into the RAM buffer is uncompressed (I'm pretty sure), and hence the data size (at that point) doesn't depend on the content.
 
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