GPS timestamp in video

[Nora]

Hello all,

can anyone tell me if a video taken by the MAvic 2 enterprise stores a GPS timestamp in every video frame or just for the start/endpoint of the video?
Thanks a lot.

 

[Keule]

Hello all,

can anyone tell me if a video taken by the MAvic 2 enterprise stores a GPS timestamp in every video frame or just for the start/endpoint of the video?
Thanks a lot.

GPS location info is not stored in the footage itself, but by enabling 'Caption ON' in the video settings, a sidecar file is created name DJI_xxxx.SRT

When you play the footage with subtitles enabled (such as VLC), the GPS Infos, along with other data are displayed on the screen.

 

[DanMan32]

I don't think the M2 or any DJI for that matter uses GPS time for its internal date/time clock but rather gets it from the app.

At least the Mini doesn't. I once flew the Mini without the phone/tablet. The video file was dated for the day I last had it connected with the app. I tried going by the flight logs until I realized without the app connected, it couldn't record any logs.
The Mini, unlike others, embeds the telemetry subtitle in the video, assuming you have it enabled in the app. No tiestamps there.

 

[Keule]

I don't think the M2 or any DJI for that matter uses GPS time for its internal date/time clock but rather gets it from the app.

All of the DJI vehicles can be flown without GO / GO4 attached. OK, then the aircraft are height and distance limited, but nevertheless photos can be shot and videos can be taken with the RC buttons. Where do the timestamps in the logs or EXIF fields come from then?

It is important for the FC to have a valid time base to have synchronized timestamps for all sensor data used while in flight.

The only valid time base is from a GNSS source. You can easily look up some of the Onboard SDK calls such as

getNMEAMsg()
getFCTimeInUTCRef()
getUTCTime (NMEAData & utc)

to retrieve timing Infos from an onboard hardware GNSS receiver.

 

[apeel]

While the GPS location / coordinate info may not to be stored, I think that the original poster (OP) was asking about the time stamp(s), which I thought was stored, and that you do not need to turn on the CAPTIONS feature. Is this not true?

 

[Keule]

While the GPS location / coordinate info may not to be stored, I think that the original poster (OP) was asking about the time stamp(s), which I thought was stored, and that you do not need to turn on the CAPTIONS feature. Is this not true?

The following image was produced with an M2ED and Caption ON:

 

[apeel]

OK. Caption provides lots of info. But if Caption is OFF then is there any time stamp at all in the video file, at least marking what tie the video started?

 

[Keule]

But if Caption is OFF then is there any time stamp at all in the video file, at least marking what tie the video started?

Yes, see EXIFTOOL output:

 

[apeel]

Thanks Keule. I hadn't heard of this tool. Will download a copy.

So, reading the Exif data seems to suggest that the start date/time and duration is recorded. From your example, under the Quicktime File section, I see:
CreateDate: 2020:03:01 14:27:43
Duration: 0:01:06

Good to know!

 

[DanMan32]

The timestamps displayed for video may only be from file system timestamp. My experience has been that without the app, AC system time is not current time but rather last time it was run with the app. Could the AC get time from GPS? Yes, and it should but my experience at least with the Mini (and I believe also with P3) is that it doesn't. Anything directly recording GPS data such as Exif or SRT might have timestamps from GPS but I suspect the SRT timestamp will be system time, not GPS time.

For the Mini last month I flew it without setting up with a phone/tablet in a rush and recorded video. That was on Saturday 2/22. The video file date was stamped 2/19 rather than 2/22. Flight logs showed I last had the Mini running on 2/19 for a minute or so.

 

[apeel]

Thanks DanMan32. I think your experience proves that the timestamp is not coming from the GPS satellites, but rather the file system time.

I have an Osmo Pocket and some experimentation with that help me figure out what DJI does with the Osmo Pocket. Basically, it has an internal clock that keeps running even when not in use (assuming the battery is still got a charge on it). Then whenever you use the DJI Mimo app to communicate with the Pocket, it resyncs its International clock to that of the phone. If you do not use the app then the Pocket still provides a timestamp based on the self running, internal clock.

I did some measurements and found that the internal clock is not at all accurate, and left to itself, will gain about 16-seconds every 24-hours of non-use. So I now connect the Pocket to the app temporarily to just to sync the clock, then use the Pocket by itself without the Mimo App. This provides reasonable accurate tome stamps.

 

[ComandorUA]

Hello
Attached files are screenshots from from video i did at end of February. Video was copied from my M2ED to computer (it is one .mp4 file only). But timestamp and GPS position is shown during hole video (upper left corner). It looks like it is included on every frame.
Also i found that longitude and latitude in stamp are mixed with each other. Video is taken in Ukraine, but if you copy coordinates as they are shown in video to google map - it will show you point in Persian Golf. You have to change coordinates positions first before searching them on google map to find correct map point.

 

[DanMan32]

Thanks DanMan32. I think your experience proves that the timestamp is not coming from the GPS satellites, but rather the file system time.

I have an Osmo Pocket and some experimentation with that help me figure out what DJI does with the Osmo Pocket. Basically, it has an internal clock that keeps running even when not in use (assuming the battery is still got a charge on it). Then whenever you use the DJI Mimo app to communicate with the Pocket, it resyncs its International clock to that of the phone. If you do not use the app then the Pocket still provides a timestamp based on the self running, internal clock.

I did some measurements and found that the internal clock is not at all accurate, and left to itself, will gain about 16-seconds every 24-hours of non-use. So I now connect the Pocket to the app temporarily to just to sync the clock, then use the Pocket by itself without the Mimo App. This provides reasonable accurate tome stamps.

It's not uncommon for electronics that aren't watches to not keep time very well. The clocks in cars are often inaccurate over time unless they have built in GPS and uses that to sync time. Even then the dashboard clock may drift since its part of a different system than the GPS is, and they don't sync with each other.

Phones are accurate because of GPS. Fitbits are accurate because they sync with the phone by Bluetooth. But if the Bluetooth connectivity is lost for days/weeks, they become inaccurate.

And so Phantoms/Mavics have wrong time until the app provides the time. The GPS is there with microsecond accuracy so why the AC doesn't sync with it is unknown

 

[AnzacJack]

Hello
Attached files are screenshots from from video i did at end of February. Video was copied from my M2ED to computer (it is one .mp4 file only). But timestamp and GPS position is shown during hole video (upper left corner). It looks like it is included on every frame.
Also i found that longitude and latitude in stamp are mixed with each other. Video is taken in Ukraine, but if you copy coordinates as they are shown in video to google map - it will show you point in Persian Golf. You have to change coordinates positions first before searching them on google map to find correct map point.

Amazing pics

 

[GadgetGuy]

Hello
Attached files are screenshots from from video i did at end of February. Video was copied from my M2ED to computer (it is one .mp4 file only). But timestamp and GPS position is shown during hole video (upper left corner). It looks like it is included on every frame.
Also i found that longitude and latitude in stamp are mixed with each other. Video is taken in Ukraine, but if you copy coordinates as they are shown in video to google map - it will show you point in Persian Golf. You have to change coordinates positions first before searching them on google map to find correct map point.

What happened to the rest of the bridge?