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Very bad fpv lag only while recording
827 7 2017-8-3
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Nazar78
Captain
Flight distance : 5063409 ft
Singapore
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v4.1.4 Android and Mavic .900 so far, no app crashing during usage. In fact, it had never once crashed in v4.1.3. It did only crash randomly while trying to change the Wifi channels.
But what baffles me since v4.1.3 I first got the Mavic two weeks ago, is the live fpv is lagging behind very badly "only while recording" in no matter 720p, 1080p or worst 4K. Once starts recording, it will slowly lag till 15++ secs. The actual footage in the Mavic's sdcard is fine. I don't need to post a video of this as it's straight forward, place both RC and AC on a table, hit record, after a while move the AC or tilt the gimbal and the fpv lags far behind. Stop the recording, slowing the fpv catches up.
I've tried refreshing the firmware, factory reset followed by all the necessary calibrations, off/on local cache, different recording size/rates, different normal/HD/smooth mode, clean reinstall the app, Note3 to force GPU rendering, no background processes. I've been researching, most have said try another device and I did try a few Androids. My Note3 (still running fast) is listed in the official supported device list and I'm not an IOS person. How do you guys overcome this lag while flying and recording (not in intelligent flight modes) especially trying to "manually" yaw focus on a moving object?
The image transmission option is selectable only in Wifi mode, in RC mode it's just an information. I think we all don't mind lowering the transmission size (which shouldn't affect the recordings in the Mavic itself) as long as the live feed keeps up. Also I got the feeling it seems that the app is trying to decode all the video frame buffers to the screen. Isn't it better for the app to have some sort of frame dropping sequence rendering to keep up with the live feed? Hence no bottleneck on the mobile device?

TIA!

2017-8-3
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Ex Machina
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United States
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That's not what I see, Image Transmission is selectable when using the RC, and fwiw I always use Normal downlink mode. It's not selectable when you are already recording, though.

So, when you say the lag only happens when recording, you mean that when not recording you can fly as long as you want and you can detect no lag in the downlink video? Do you have caching turned on? That suggests to me that the device is not up to the task at hand, or you have some other live processes that are tying up CPU cycles or throughput.

If you really can't change the Image Transmission mode while hooked up to the RC, connected to the Mavic and ensuring recording is not happening, then maybe you should try a clean install of the app, because you definately should be able to do that, whether on iOS or aOS.

2017-8-3
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Ex Machina
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After a re-read of your post I see you've already tried my suggestions to no avail, still, the fact remains that you should be able to change Image Transmission modes when hooked up to the Mavic via RC, and lag only while recording should be clues to where the problem lies.
2017-8-3
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DJI Susan
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Actually, the image transmission settings can be set as Normal Mode, HD Mode and Smooth Mode when connected RC. I would recommend you to try and confirm. Also, I do not promote to buy iOS devices, but it will be helpful to verify which may cause the issue.
2017-8-3
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Nazar78
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Flight distance : 5063409 ft
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Ex Machina Posted at 2017-8-3 19:25
After a re-read of your post I see you've already tried my suggestions to no avail, still, the fact remains that you should be able to change Image Transmission modes when hooked up to the Mavic via RC, and lag only while recording should be clues to where the problem lies.

Hello Ex Machina!


Thanks for replying.

That's not what I see, Image Transmission is selectable when using the RC, and fwiw I always use Normal downlink mode.
Sorry if I'm not clear, when in RC mode, the "Image Transmission Code Rate" (below the "Image Transmission Mode" Regular/HD/Smooth) only shows a Mbps horizontal bar which can't be changed. While in Wifi mode, there's a new option "Image Transmission Quality" 1/2/4Mbps. So while in Wifi mode if I get lags, I can change it to 1Mbps and situation improves. But in RC Mode the option for "Image Transmission Mode" is already the default "Regular mode" which I believe the lowest? And I can't adjust the "Image Transmission Code Rate" horizontal bar to always stay lower Mbps, it's just displaying the current bitrate.

So, when you say the lag only happens when recording, you mean that when not recording you can fly as long as you want and you can detect no lag in the downlink video?


Yes correct. It starts to lag behind slowly only while recording even though the HD icon indicates full bar.

Do you have caching turned on?
I've tried both caching on and off. I even cleared the data apps leftovers via shell adb and reinstalled.

That suggests to me that the device is not up to the task at hand, or you have some other live processes that are tying up CPU cycles or throughput.
This is what I'm afraid of. I have the good old still speedy Note3 (stock rom but rooted, self compiled kernel and modded to my likings) and I'm pretty much in control of the phone foreground/background. Well guess I have to wait for Note8 Skipped several generations as it's not worthy of an upgrade.
2017-8-3
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Nazar78
Captain
Flight distance : 5063409 ft
Singapore
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DJI Susan Posted at 2017-8-3 22:25
Actually, the image transmission settings can be set as Normal Mode, HD Mode and Smooth Mode when connected RC. I would recommend you to try and confirm. Also, I do not promote to buy iOS devices, but it will be helpful to verify which may cause the issue.

Hello Susan,

Thanks for replying!

Yes I'm aware that the "Image Transmission Mode" can be changed to Regular/HD/Smooth. It's already in the default Regular mode which I believe the lowest transmission quality. But the fact that "Image Transmission Code Rate" can't be changed, it's just a horizontal bar Mbps indicator.


I think it would really help those having live video lag issues on their phone if this "Code Rate" can be adjusted in RC mode just like it's possible to change it while in Wifi mode.


Also the app should be smart enough to detect massive lag in the fpv then intelligently start dropping a few backlog frames decoded to the screen to keep up with the live feed. Appreciate if you could help to relay this request to the app devs.
2017-8-3
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Angelo26
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Flight distance : 799718 ft
Austria
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So You can be happy ! At LEAST You can fly Your MP without crashes of DJI-CRAP 4 - oh, sorry GO4............... Both my official DJI-certified Note 4´s, wiped clean of all other apps, uninstalled,wiped GO4 and reinstalled, used only in airplane mode, crashes EVERY flight after 10-15 minutes and video-transmission-lag starts from the very beginning of EVERY flight. Commands of C1-button (Gimbal up/down) lag from the very beginning of every flight by 15-20 seconds ................ GO4 is a mess, just look at ratings in Playstore. Everything worked fine with GO3 back in Dec. 2016 until DJI messed up with GO4 ...........
2017-8-4
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Nazar78
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Singapore
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[FIXED!] RE: Very bad fpv lag only while recording

Angelo26 Posted at 2017-8-4 00:27
So You can be happy ! At LEAST You can fly Your MP without crashes of DJI-CRAP 4 - oh, sorry GO4............... Both my official DJI-certified Note 4´s, wiped clean of all other apps, uninstalled,wiped GO4 and reinstalled, used only in airplane mode, crashes EVERY flight after 10-15 minutes and video-transmission-lag starts from the very beginning of EVERY flight. Commands of C1-button (Gimbal up/down) lag from the very beginning of every flight by 15-20 seconds ................ GO4 is a mess, just look at ratings in Playstore. Everything worked fine with GO3 back in Dec. 2016 until DJI messed up with GO4 ...........

Yeah somehow the app's optimization (crash and/or lag) is totally not acceptable for mid-range Android devices! As a developer myself, I'm astounded. There could be possibility of trying on a custom rom but unfortunately not everyone is willing or knows how to accomplish this.

To all, just to report back that I've managed to fix this live feed lag during recording issue. Have been tweaking back and forth for few days with no luck then finally I flashed a custom kernel (thanks to Audax dev, an awesome kernel) on my Samsung Note3 latest Feb 2017 stock rom N9005. Although it's capable of overclocking to 2.7GHz, I leave it at stock 2.3GHz (battery friendly) and applied -50mv undervolt across all the frequencies. For personal preference, I also increased the VM heapsize to 768MB, disabled the Zswap and enabled write delay.


I suspected due to the unoptimized intensive activities in the DJI app, heat was throttling down the phone. I can play other 3D games without this excessive heat. The phone which screen was set to dim, no background tasks and flying in airplane mode, was quite hot after awhile and I was flying during a cool evening around 28deg (tropical city). DJI devs should really look into this especially the one I mentioned in the previous few replies (frame dropping sequence rendering). Now after this fix, with maxed brightness and while not even in airplane mode (I also left few tasks running in bg, didn't kill any tasks and disabled USB charging), the 4K-30fps/1080p-96fps recording (64GB UHS-I card) live feed is totally lag free!


2017-8-15
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