This question is about how a video is written to an SD card, and how the DJI camera software monitors the process to determine if a video file was successfully written to disk -OR- what happened, if the write failed.

The reason for the question is try to understand what happened in a recent flight where I shot several videos, but found the MP4 files were missing from the SD card.  Adding to the mystery is that each of those missing MP4 files DOES have a corresponding THM file, and the date/time stamp corresond to the time the videos were shot  So a THM file is written, but the corresponding MP4 is NOT???  

I always make a screen recording of all my flights, and can confirm that there was no indication of any problems inflight.

Is the DJI camera software not capable of determining SD write failures, and record that fact in some log file?

How can I prevent this kind of a problem in the future? After I noticed the missing files, I wanted to see if the problem was still there, so I tried to record and playback a short video, and had no issues.  I have had this top of the line Sandisk 64G SD card for over two years,  with no problems whatsoever.

PLEASE HELP ME FIND OUT WHAT HAPPENED!

Did the AC get shut off abnormally ?

If it was then  put a fresh battery in and restart the AC, this might complete the file saving process

lannes Posted at 7-18 20:16
Did the AC get shut off abnormally ?

If it was then  put a fresh battery in and restart the AC, this might complete the file saving process

AC shutdown was completely normal.  In fact, the video was followed by a panorama series which recorded properly, so there was plenty of time for the video file to close.
Also, note that there were actually 3 video files in a row that are missing.

The first thing to try is to copy off any files on the card you wish to keep, then place the card back in the aircraft and use the utility in the app to format the card in the aircraft.

Geebax Posted at 7-19 14:58
The first thing to try is to copy off any files on the card you wish to keep, then place the card back in the aircraft and use the utility in the app to format the card in the aircraft.

I've already copied off the files, and was planning to do the reformat, but I've been holding off, until I find out what went wrong and how to prevent it from happening again.  If there's anything on that card that would provide a clue, I don't want to wipe it away.

Several days ago, I bought a 32G version of the same card, and have tested it for capacity, and read/write rates.  I will reformat that card in the Mavic Air using the format command in the GO4 app.

My question, to anyone who can answer - HELLO DJI - did the DJI software fail by not recognizing the write failure, or does its design assume that writes are successful (that would be a poor design).

Anybody know how to get this before knowledgeable DJI technical people?  I spent over a half an hour waiting on hold, before I got to a real person, and all he could offer was to reset the camera, and reformat the card.  He apparently didn't know any more of what I could do, and could not answer the question about recognition of a write failure.  

My drone and camera appear to be working correctly, without DJI's help.  The problem remains that without knowing what happened, how am I supposed to have confidence that it won't happen in the future??  My question should be very easy for the right people to answer, definitively.  I would expect that the DJI software would monitor the SD card interface, verify successful writes, and record any failures to some kind of log file, and notify the user of the failure.  Simple question: does it do this or not?

MAPilot Posted at 7-20 09:41
I've already copied off the files, and was planning to do the reformat, but I've been holding off, until I find out what went wrong and how to prevent it from happening again.  If there's anything on that card that would provide a clue, I don't want to wipe it away.

Several days ago, I bought a 32G version of the same card, and have tested it for capacity, and read/write rates.  I will reformat that card in the Mavic Air using the format command in the GO4 app.

Please understand that you do not get technical advice from DJI on this forum, the only help you get is from the members. And their support call centres are manned by unskilled people who only know how to advise you to send the aircraft back for repair.

What DJI do not tell you is that the aircraft writes lots of hidden files to the SD card that clutter up the card and slow it's write cycle down. The best way to fix this is to periodically do a format of the card.

Does the software check that a successful SD card write has been performed, hmm, somehow I doubt it.

MAPilot Posted at 7-20 09:41
I've already copied off the files, and was planning to do the reformat, but I've been holding off, until I find out what went wrong and how to prevent it from happening again.  If there's anything on that card that would provide a clue, I don't want to wipe it away.

Several days ago, I bought a 32G version of the same card, and have tested it for capacity, and read/write rates.  I will reformat that card in the Mavic Air using the format command in the GO4 app.

The problem remains that without knowing what happened, how am I supposed to have confidence that it won't happen in the future??  
You could do a little testing and over time when you don't see this happening, you gradually get confidence.
In 6 years of involvement with DJI drones and forums, your post is the first I've seen asking about this.
I suspect there's nothing wrong with your camera.

Hi. I am sorry for the trouble this has caused. With regards to this matter. I will forward this thread and concern to the designated DJI support team for further attention. Again, I am sorry for the trouble. Thank you.

DJI Paladin Posted at 7-20 19:32
Hi. I am sorry for the trouble this has caused. With regards to this matter. I will forward this thread and concern to the designated DJI support team for further attention. Again, I am sorry for the trouble. Thank you.

Thank you.

I'm looking forward to seeing what comes from your "further attention"; I have literally spent hours with this issue, on this, and other, forums.
While I've only used drones for about 2 years, as a consumer, I'm a retired engineer from the aerospace industry, with substantial experience in systems development, from writing requirements to testing and fielding of systems. I can assure you that if we provided the kind of support you are providing, I would have been an unemployed engineer a long time ago!

I intend to follow through on this matter, and expect your people to contact me by PM.

Labroides Posted at 7-20 16:56
The problem remains that without knowing what happened, how am I supposed to have confidence that it won't happen in the future??  
You could do a little testing and over time when you don't see this happening, you gradually get confidence.
In 6 years of involvement with DJI drones and forums, your post is the first I've seen asking about this.

My confidence will depend on how DJI responds.
Good to hear that this is not a common problem.

Geebax Posted at 7-20 15:16
Please understand that you do not get technical advice from DJI on this forum, the only help you get is from the members. And their support call centres are manned by unskilled people who only know how to advise you to send the aircraft back for repair.

What DJI do not tell you is that the aircraft writes lots of hidden files to the SD card that clutter up the card and slow it's write cycle down. The best way to fix this is to periodically do a format of the card.

Yes, I’m certainly getting that impression.

Their telephone support is not impressive either; over half an hour waiting in the queue, the silence being broken only by that obnoxious “sorry for the delay” message. And when I finally got a person, his answer was to reset the camera, but he couldn’t answer my basic question about the warning of a disk write failure. He put me on hold for a minute or two (to consult, I assume) but when he got back, I was no closer to an answer. DJI could save a ton by just replacing that tech support with a diagnosis tree on their website.

Your observation about tons of files is something I was noticing too. My most disturbing discovery was a file that I couldn’t identify, which took a whopping 7+ GB!  I thought I may have accidentally deleted the videos, so I inspected the SD card with several “undelete” programs...that’s a subject for another day. Limitations on Demo versions constrained that effort.  At this point, it’s pretty clear to me that every time I move files off of the SD card, I should routinely reformat the card, removing all the accumulated junk, especially since it only takes a few seconds.

As to the write failure detection, I’m not familiar with the SD card interface, but I’d be shocked if it doesn’t include some kind of write status. I’m not talking about redundancy/failover, just confirmation that commands are successfully completed, and recording somewhere when there is a failure.

MAPilot Posted at 7-21 05:19
Yes, I’m certainly getting that impression.

Their telephone support is not impressive either; over half an hour waiting in the queue, the silence being broken only by that obnoxious “sorry for the delay” message. And when I finally got a person, his answer was to reset the camera, but he couldn’t answer my basic question about the warning of a disk write failure. He put me on hold for a minute or two (to consult, I assume) but when he got back, I was no closer to an answer. DJI could save a ton by just replacing that tech support with a diagnosis tree on their website.

"As to the write failure detection, I’m not familiar with the SD card interface, but I’d be shocked if it doesn’t include some kind of write status. I’m not talking about redundancy/failover, just confirmation that commands are successfully completed, and recording somewhere when there is a failure."

Since there is apparently no error message for write failure (or more to the point I have never heard anyone say they have seen such a message) I assume there is no write completion check.

Notwithstanding your experience as an engineer, go back to basics.
The fault is either with the drone or the card and the issue might be temporary or intermittent.
Reset the camera. I know DJI trot this out, but often it does clear up anoying issues. It isnt hard to do so why not?
You don't need to fly the drone to record video, so you can do the tests at your desk.
First check the drone by using a different SD card. Format it in the drone first and then record video.
Take long recordings and some short ones. Play them to see if everything has been recorded properly.
assuming the drone is fine, do the same test with the other (suspect) card. I suggest you read the technical stuff from the SD card manufacturer about the benefits or otherwise of constantly reformatting as against deleting data. Don't rely on forums or Youtube, because only the manufacturer will know for certain.
I had a Kingston SD card suddenly become unreadable and they replaced it without quibble, and I didn't need to post it back to them. Speak to your manufacturer.
Let us know what you discover.
Good luck.

AlansDronePics Posted at 7-21 23:08
Notwithstanding your experience as an engineer, go back to basics.
The fault is either with the drone or the card and the issue might be temporary or intermittent.
Reset the camera. I know DJI trot this out, but often it does clear up anoying issues. It isnt hard to do so why not?

Agree that the fault is either in the drone or the card. No doubt it is not permanent, since I was able to record and playback a video after the lost video incident.

I called DJI tech support, and explained the situation, and one of the first things he mentioned was the camera reset.  My concern about doing a camera reset was that the counter would reset to zero.  This was resolved when I found out how to manually set the counter to the latest number used.  The reset was very quick, and all seems OK.

Another thing the DJI agent mentioned rather early was reformatting the SD; he didn't use the words, but it was obvious that there is a lot of "junk" that accumulates in the memory.  I formatted the internal memory, as well as a new 32G Sandisk card, using the format command in the GO4 app for both.

Reformatting vs. deleting files, pro and con, is still an open topic for me, but if I'm not worried about using write cycles, and I'm not, there seems to be no reason not to format, if not every time, then at least periodically.  I think most people would rather watch their SD capacity go down slowly (wearing out) rather than having some trash causing an unnoticed write failure.  Still waiting on responses to a few feelers I put out.

I was told that the .DAT log files, from the aircraft, contain data that DJI can use to determine why the write failed,  and there was no anomaly indicated on the display.  I'm now trying to use DJI Assistant to download those files so I can send them to DJI.

When I fire up Assistant, it shows me connected to a Mavic named orange30.  Makes no sense to me.  I am using v1.1.2, which is not the most current one, but it's the last one that lets you edit many of the flight parameters.  Anybody know where I can find step by step instructions for connecting to Mavic Air, and downloading the DAT files?  Many months ago I was able to connect to my Mavic Air, but I'm not sure about the version I used.

MAPilot Posted at 7-26 18:37
Agree that the fault is either in the drone or the card. No doubt it is not permanent, since I was able to record and playback a video after the lost video incident.

I called DJI tech support, and explained the situation, and one of the first things he mentioned was the camera reset.  My concern about doing a camera reset was that the counter would reset to zero.  This was resolved when I found out how to manually set the counter to the latest number used.  The reset was very quick, and all seems OK.

As far as I am aware, the DAT files are encrypted, so downloading them is not going to help you much.

I believe the hardware in the aircraft consists of several systems-on-silicon and probably has an ARM32 architechture. The video processor would really have to be multi-threaded, as it has to deal with three seperate streams of video, the main full resolution stream recorded to the SD card, the lower resolution stream recorded to the THM file and the stream that is transmitted back to the RC unit as the FPV feed. So, at a minimum, there has to be 3, possibly more,  concurrent files being written to the SDcard, the main file, the THM file, the flight log and and probably an error file. In light of that, it is not surprising that you need a fast, uncluttered SD card to make everything work as expected.

As to formatting vs. deleting files, when you delete files, you are only able to delete those you can seen, and DJI make use of a lot of hidden directories and hidden files, so rubbish can easily build up if you are not looking for it. The format utility on the other hand, cleans up everything.

Sadly, we are not given access to any of the DJI development people, only the support call centre people, who most likely are in a Phillipine call centre and have never owned or flown a DJI product.