weirdness with 120 fps

Dome · Mar 30, 2016

Anyway 120fps seems to have some problem.
Note that mbps reading is fake due to error in the mp4 header produced by the p4. The correct transfer rate reading is relative to fps indicated in the header. For example if it show 30fps (and you shoot 120fps) and indicate 12Mbps, then you need to times by 4 = 48Mbps

AlexLim · Mar 30, 2016

Sal Ferrari said:
Has ANYONE else tried 120 fps or am I the only one?

If so, please let me know if they work properly for you thanks.

I didn't have most of those playback/import problems... but I think the 120fps quality is total crap. It's super blurry, noisy, and cropped like crazy, so it's not really 'usable' like proper footage.

It was only a small part of my decision to buy, since I shoot 4k most of the time, but I do wish someone out there, an early reviewer, would have mentioned that 'oh yea btw, yes it shoots 120fps at 1080p, but it looks like poop'.

m0j0 · Mar 30, 2016

Again I am guessing but I'm betting this explains the issue..

The reason the quality is lower is because it is actually overcranked 30p (29.97).

To put things in perspective, when you’re shooting at 60mbps at 30p (29.97) you are essentially spreading out that 60mbps of data over only 30 (29.97) frames, whereas when you’re shooting at 120fps you are getting the exact same amount of data per second, but now you are spreading it out over 4 times the amount of frames, which means each frame gets 4 times less information in it.

For the quality to remain the same for each frame the data rate would have to increase 4 fold.

Fallguy · Mar 30, 2016

I've been filming 1080P at 60fps without any issues. I did a side by side comparison indoors with that and 2k and 4k and it seemed like the best route to go was the one I chose. Less space I believe used on the sdcard , and maybe not as zoomed in if I can remember correctly. Still huge disappointment on the 120fps.

Dome · Mar 31, 2016

m0j0 said:
Again I am guessing but I'm betting this explains the issue..

The reason the quality is lower is because it is actually overcranked 30p (29.97).

To put things in perspective, when you’re shooting at 60mbps at 30p (29.97) you are essentially spreading out that 60mbps of data over only 30 (29.97) frames, whereas when you’re shooting at 120fps you are getting the exact same amount of data per second, but now you are spreading it out over 4 times the amount of frames, which means each frame gets 4 times less information in it.

For the quality to remain the same for each frame the data rate would have to increase 4 fold.

I don't think the p4 is really recording at 30fps. It works at 120fps but the firmware has some bug so it save header as 30fps. The quality of the video can be not good for the same firmware glitch. At 120fps you need at least an exposure shutter at 1/240, but better around 1/300.

m0j0 · Mar 31, 2016

No it isn't recording at 30fps. It is recording at120fps. Without getting too technical. It is recording with the same bitrate at 30 and 120. That's why the video looks degraded.

Sent from my iPad using PhantomPilots mobile app

OmegaStageThr33 · May 16, 2016

m0j0 said:
No it isn't recording at 30fps. It is recording at120fps. Without getting too technical. It is recording with the same bitrate at 30 and 120. That's why the video looks degraded.

Sent from my iPad using PhantomPilots mobile app

I am having the same issues. 120fps looks like junk and the file is stamped with 29 frames/second in windows. I am using a ScanDisk 32Gb that supports 95MB/sec.

kmeta · May 16, 2016

I also try 120 fps recording and confirm that video is crap and blury.

m0j0 · May 16, 2016

It is overcranked to 120 basically you are getting the same bitrate as 30 fps... Which is why it appears degraded... Because as compared to 30 fps there is less data per frame. Which is about 1/4 the amount of data per frame.

OmegaStageThr33 · May 16, 2016

m0j0 said:
It is overcranked to 120 basically you are getting the same bitrate as 30 fps... Which is why it appears degraded... Because as compared to 30 fps there is less data per frame. Which is about 1/4 the amount of data per frame.

I get you. That's pretty shady advertising if its intended to be that way. Why would they do this? My iPhone's 1080p 120fps looks 10000 times better. Does the camera max out the 60Mbps bit rate at 4K 30fps? If thats the case, I would assume 1080p uses 1/4 the bit rate, but then jacking it back up to full when in 120fps mode. Is this not correct?

Has anyone from DJI commented on this issue?

[EDIT] Holy crap, just tried calling them and I was #34 in-line. Wow.

OmegaStageThr33 · May 16, 2016

m0j0 said:
Again I am guessing but I'm betting this explains the issue..

The reason the quality is lower is because it is actually overcranked 30p (29.97).

To put things in perspective, when you’re shooting at 60mbps at 30p (29.97) you are essentially spreading out that 60mbps of data over only 30 (29.97) frames, whereas when you’re shooting at 120fps you are getting the exact same amount of data per second, but now you are spreading it out over 4 times the amount of frames, which means each frame gets 4 times less information in it.

For the quality to remain the same for each frame the data rate would have to increase 4 fold.

If this was the case, then wouldn't the 4K @30fps video quality have the same crap bit rate? The 4K video looks much better to me than the bit rate I'm seeing with 1080p @120fps

m0j0 · May 16, 2016

it isn't shady. It actually works really well in my GH4. You just don't have sound.

Fallguy · May 16, 2016

This was my other thread on this issue Filming 120FPS . Felt like I was beating a dead horse . After I put up a video I had of my son that was taken with my Gopro Hero 4 black in 120fps then slow down in post , I dared anyone to come up witha video comparable to it with the garbage that DJI claims to be 120fps.

OmegaStageThr33 · May 17, 2016

Fallguy said:
This was my other thread on this issue Filming 120FPS . Felt like I was beating a dead horse . After I put up a video I had of my son that was taken with my Gopro Hero 4 black in 120fps then slow down in post , I dared anyone to come up witha video comparable to it with the garbage that DJI claims to be 120fps.

Have you contacted DJI about this?

Sal Ferrari · May 19, 2016

OmegaStageThr33 said:
Have you contacted DJI about this?

i tried but they would not acknowledge the problem. it was extremely frustrating dealing with them so i gave up. they made me jump thru hoops and then still offered no explanation or help with the issue. good luck.

OmegaStageThr33 · May 19, 2016

Sal Ferrari said:
i tried but they would not acknowledge the problem. it was extremely frustrating dealing with them so i gave up. they made me jump thru hoops and then still offered no explanation or help with the issue. good luck.

Wow... I'll try today, hopefully I have better luck. If not, I'm glad I have a 45 day return window through Best Buy.