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Grainy footage + Loss of Power Causing Drone to Crash?
575 23 2020-5-27
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MADagain
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New to this whole drone thing... so got a few questions for people who have been flying for a while.
Has anyone had the battery come out of the Mavic Mini (even whilst using the propeller gaurds) after a small impact? I managed to get the protective glass on the gimbal/camera to shatter after the battery compartment dislodged and the battery slipped out a bit so the drone lost power. Now you might sit there and think that I'm down playing that... but no it wasn't a fast or hazardous crash it was a slight bump on my shed and next thing I know the drone lost power and dropped to the floor... on concrete??

So my question is, for people who have the Mavic Mini are the price cuts worth the risk of total device failure even if you try to minimise them yourself?

My second question is about the Mavic Mini's video quality. I haven't been able to record a video without grain no matter what my settings are, for example I've tried ISO 100, SS @ 800 (or above when it's bright outside) with either 1080p @ 30fps and 60fps and have also tested 2.7k @ 24-25 and 30fps. With little to no reduction in video noise... is this a faulty unit, a result of high shutter speeds or is this actually what the drone records? (I'm not even going to talk about the oversharpened images/footage).

I've seen many videos on the internet showing how amazing the footage looks, lack of grain and minimal compression artifacts but I've had nothing but issues??

Keep in mind I've only had this thing for 5 days now. I do have DJI Care Refresh, would it be worth replacing with Care Refresh or to replace/fix under warranty?

2020-5-27
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itchyeyeballs
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Hi,

Were you flying with the Gimbal cover on or did you smash the lens itself?

Generally, the video quality is good, what are you using to view/edit the footage?

The best advice to improve quality is usually to fly slower but now that you have manual control over the shutter speed you can purchase ND filters to help incorporate motion blur for smoother videos.
2020-5-27
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MADagain
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itchyeyeballs Posted at 5-27 03:35
Hi,

Were you flying with the Gimbal cover on or did you smash the lens itself?

No, the gimbal has protective glass over the lens, it's held on with adhesive.

Using Adobe Premiere Pro to view footage, but even with VLC Media player on my computer it still shows a lot of grain.

Kinda pointless to allow control of shutter speed to... remove grain from day dot. It seems like a sensor issue not a shutter speed issue...
2020-5-27
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itchyeyeballs
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MADagain Posted at 5-27 06:00
No, the gimbal has protective glass over the lens, it's held on with adhesive.

Using Adobe Premiere Pro to view footage, but even with VLC Media player on my computer it still shows a lot of grain.

Was there any noticeable difference in the image quality before and after the crash?

Do photos have the same issue? Can you post a sample video? users on here will be able to tell you if looks ok or not.
2020-5-27
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MADagain
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itchyeyeballs Posted at 5-27 06:08
Was there any noticeable difference in the image quality before and after the crash?

Do photos have the same issue? Can you post a sample video? users on here will be able to tell you if looks ok or not.

Yeah sure can, here's a google drive link with before and after the crash.

DJI_0006 is Before
DJI_0019 is After.

https://drive.google.com/drive/folders/1V6KGBrRxDvgatxALGSOk6d5y1mZhfugo?usp=sharing
2020-5-27
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MADagain
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Update, I've noticed that the SD card I've been using is a SanDisk Ultra class sd and that could be why I'm noticing grain and an unstable bitrate.

Anywhere from 32MBps to 35MBps, compared to the advertised 40MBps bitrate of the drone.

But seeing as 40MBps is the max for any resolution on the Mavic Mini that means even with the larger resolution of 2.7k the bitrate will still be the same as 1080p?? So it could be a design issue meaning that 2.7k will always be a little bit grainy or break during compression.

Would be interesting to see the difference, I'm gonna go out today and fly a bit more just to see if it is the SD card.
2020-5-27
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Geebax
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MADagain Posted at 5-27 20:46
Update, I've noticed that the SD card I've been using is a SanDisk Ultra class sd and that could be why I'm noticing grain and an unstable bitrate.

Anywhere from 32MBps to 35MBps, compared to the advertised 40MBps bitrate of the drone.

The Sandisk Ultra series of SD cards are not recommended, as they are borderline in terms of writing speed, you should be buying the Extreme Pro series of Sandisk cards. But in any event, the card will have no effect whatsoever on your perceived issue of grain, it is a digital recording, and it cannot affect the quality of the video image. I looked at you two clips, the one in the forest is quite obvious, it is humungeously under-exposed, hence the grain. The one at the seaside is better, but still under-exposed. The small sensor of the Mini requires you to get the light levels up as high as you can without over-exposing.
2020-5-27
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MADagain
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Geebax Posted at 5-27 21:43
The Sandisk Ultra series of SD cards are not recommended, as they are borderline in terms of writing speed, you should be buying the Extreme Pro series of Sandisk cards. But in any event, the card will have no effect whatsoever on your perceived issue of grain, it is a digital recording, and it cannot affect the quality of the video image. I looked at you two clips, the one in the forest is quite obvious, it is humungeously under-exposed, hence the grain. The one at the seaside is better, but still under-exposed. The small sensor of the Mini requires you to get the light levels up as high as you can without over-exposing.

Grain would be a result of the sensor not getting enough light and not being able to write to the card fast enough, so instead of detail it records artifacts or grain to fill in the space it can't draw data for. So that means no good for night footage haha, although the scene at the beach is underexposed also but only slightly it shouldn't have caused grain at any point.

It's either over exposed or under exposed, never perfect exposure as the lighting conditions would of blown out the entire image. May look into getting ND filters, a shame the mini doesn't come with any in the fly more kit and at the moment there's no official ND filters from DJI...
2020-5-27
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Geebax
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MADagain Posted at 5-27 21:51
Grain would be a result of the sensor not getting enough light and not being able to write to the card fast enough, so instead of detail it records artifacts or grain to fill in the space it can't draw data for. So that means no good for night footage haha, although the scene at the beach is underexposed also but only slightly it shouldn't have caused grain at any point.

It's either over exposed or under exposed, never perfect exposure as the lighting conditions would of blown out the entire image. May look into getting ND filters, a shame the mini doesn't come with any in the fly more kit and at the moment there's no official ND filters from DJI...

"Grain would be a result of the sensor not getting enough light and not being able to write to the card fast enough,"


The first part of that statement is right, grain is the result of insufficient light. The second part is not. The image is passed to an MPEG realtime encoder function inside an SOC and it is encoded digitally and has no idea what it is encoding. The card cannot have any affect on the quality of the image, it is either fast enought to keep up with recording the MPEG stream, or it is not. If it is not fast enough, it simply stops recording.
2020-5-27
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MADagain
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Geebax Posted at 5-27 22:10
"Grain would be a result of the sensor not getting enough light and not being able to write to the card fast enough,"

The first part of that statement is right, grain is the result of insufficient light. The second part is not. The image is passed to an MPEG realtime encoder function inside an SOC and it is encoded digitally and has no idea what it is encoding. The card cannot have any affect on the quality of the image, it is either fast enought to keep up with recording the MPEG stream, or it is not. If it is not fast enough, it simply stops recording.
If it's not fast enough to write data... It won't just stop it won't be "encoded" at full speed... Hence the lower bitrate which means yes it will affect the image. If it's not fast enough to write at 30 fps but can do 24fps but at day 25MBps that is hindering the image quality.

But yeah it would stop recording if it can't keep up with the data rate you desire.
2020-5-27
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Geebax
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MADagain Posted at 5-27 22:12
If it's not fast enough to write data... It won't just stop it won't be "encoded" at full speed... Hence the lower bitrate which means yes it will affect the image. If it's not fast enough to write at 30 fps but can do 24fps but at day 25MBps that is hindering the image quality.

But yeah it would stop recording if it can't keep up with the data rate you desire.

I'm sorry, but you do not understand the principle of MPEG encoding. When the SD card write process has begun, the encoder has already encoded the data and cannot 'go back and slow it down' if the write speed is not sufficient. The lower bitrate can only be achieved via a higher rate of compression, and there is no provision in the process to 'do it again at a higher compression level and lower bitrate'.

And there is no appreciable buffer in the DJI drones to buffer the data stream until the SD card 'catches up. The small buffer is sufficient to allow  a series of still shots to be taken in a bracket, but not great enough to buffer streaming video.
2020-5-27
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itchyeyeballs
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MADagain Posted at 5-27 06:36
Yeah sure can, here's a google drive link with before and after the crash.

DJI_0006 is Before

I can't see much in the before video but the other one looks ok (apart from the exposure), seems on a par with other mini footage so doesn't seem like you have a technical issue.

Try to get some videos in the "golden hour" https://en.wikipedia.org/wiki/Golden_hour_(photography)
this is when lighting is the best.

I've ordered some ND filters for mine as I'm often trying to film fast movement.

2020-5-28
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MADagain
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itchyeyeballs Posted at 5-28 00:40
I can't see much in the before video but the other one looks ok (apart from the exposure), seems on a par with other mini footage so doesn't seem like you have a technical issue.

Try to get some videos in the "golden hour" https://en.wikipedia.org/wiki/Golden_hour_(photography)

Agreed, though I've still seen many lower light videos of the Mavic mini and they still look good, with no editing so I'm just not certain this is how it's meant to behave.
2020-5-28
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itchyeyeballs
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MADagain Posted at 5-28 05:00
Agreed, though I've still seen many lower light videos of the Mavic mini and they still look good, with no editing so I'm just not certain this is how it's meant to behave.

what shutter speed did you set for the dark one? were you using the histogram for either?
2020-5-28
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MADagain
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itchyeyeballs Posted at 5-28 06:05
what shutter speed did you set for the dark one? were you using the histogram for either?

I exposed for above the trees in the first one and just started taking some video. Though wanted to show clear grain in both situations
2020-5-28
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itchyeyeballs
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MADagain Posted at 5-28 07:10
I exposed for above the trees in the first one and just started taking some video. Though wanted to show clear grain in both situations

I don't mean this to sound rude (I'm at a very similar stage with same concerns/questions) but..

get your composition and exposure right first, if the grain is still bothering you at that point then it's a problem, right now it's a potential side issue
2020-5-28
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22340179
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The first video looked ok to me. The second is in a very dark location. The mini has a small sensor so in poor light you are going to get a bit of noise. It's like any camera. The bigger your sensor the better it handles low light. I flew in low afternoon light yesterday and the footage wasn't great. You have to be in the right place at the right time to get the best result.
2020-5-28
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GaryDoug
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Excuse me if this sounds a bit rude. But are you using the actual files from the SD card and not the cached files on the phone? Something is not right there and it just looks like a lower resolution than you would expect.
2020-5-28
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DJI Stephen
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Hi there MADagain. I am sorry to read and to now about your previous flight with your DJI Mavic Mini. Kindly please contact our DJI support team at the link below to open a case for the said drone and we will submit a data analysis to find out the cause of the said crash. In addition, we will provide you with the corresponding information based on the analysis result. Again I am sorry and have a safe flight always.

http://www.dji.com/support
2020-5-28
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MADagain
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GaryDoug Posted at 5-28 18:36
Excuse me if this sounds a bit rude. But are you using the actual files from the SD card and not the cached files on the phone? Something is not right there and it just looks like a lower resolution than you would expect.

I dump all files on my computer from the SD card so yeah
2020-5-28
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MADagain
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Turns out it was the Mavic Mini, sent in to DJI for repair and they needed to swap out the gimbal + the internal circuit board. After the drone returned, it focused as expected and the footage was decent.

So remember folks, if the package is damaged, don't accept it... Most likely had a really hard hit during shipping or mishandled at some point, the box had a huge dent and minor rip in the box when I received it.

However I've upgraded to the Mavic air 2 now!!
2020-6-25
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AtPlaces
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the thing is, the drone battery does inted to fall off on hard impact- my friend has had the same issue.
2-28 16:12
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MADagain
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AtPlaces Posted at 2-28 16:12
the thing is, the drone battery does inted to fall off on hard impact- my friend has had the same issue.

It wasn't even that tough of an impact, it was more so the thin plastic warped enough to dislodge the battery. With any normal sized drone I wouldn't have expected this... so I will admit I wasn't expecting it here either.

However the front glass should be a replaceable part since it will be damaged on impact regardless. So I think that was an oversight on DJI's behalf.
5-15 11:52
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Labroides
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MADagain Posted at 5-15 11:52
It wasn't even that tough of an impact, it was more so the thin plastic warped enough to dislodge the battery. With any normal sized drone I wouldn't have expected this... so I will admit I wasn't expecting it here either.

However the front glass should be a replaceable part since it will be damaged on impact regardless. So I think that was an oversight on DJI's behalf.

With any normal sized drone I wouldn't have expected this
It's very common for the battery to be released with the impact of a crash even with larger drones.
5-15 14:38
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