video gps time

[mert]

hi,
I want to synchronize my photos with sensitive GPS measurements in time.

I have a 17.52 minute video file. I split this file at 1 per second. I got a total of 1052 frames.

Code Select Expand

exiftool -ee -c "% .7f" -gps * -time: all * .MP4

Using this command I got the times in every second.

I got a total of 1051 GPS times from here.
GPS time of 1 second photo in between is missing.

what is the reason for this?

When calculating the times, this code gives the first frame time of the first second or the time of the last frame.?

[Phil Harvey]

ExifTool just extracts the GPS times that are stored in the file.  Nothing more.

There are extra spaces that shouldn't be there in your command, but it sounds like they wheren't there when you ran it.

- Phil

[mert]

thank you phil.

my command is like this.

Code Select Expand

exiftool -ee -c "%.7f" -gps*-time:all 1.MP4

When splitting a 30 fps video into pictures. Is the first picture it produces is the 30th frame of the first second or the zeroth frame?

[Phil Harvey]

Again the spaces in your command are wrong.

But there are 3 reasons I can't answer your question:

1. Your english is very poor and I don't understand exactly what you are asking

2. There are more than 30 ways that GPS is stored in MP4 videos and I don't know which method your file uses.

3. GPS data is typically asynchronous to video frames.  The timestamps must be used to associate it with the video.

- Phil

[mert]

firstly sorry for poor english,

The problem is extracted frame number. The video was recorded using GoPro Hero 7. I checked the start and finish time of the video by code below, you also may see the time below. The length of the video is 8 minutes and  51 seconds. According to output of the code, there should be 533 photos depending on the start time and finish time. But the code gave 532 GPS date time. Also, I split the video to obtain photos in every per second by free video to jpg converter [https://www.dvdvideosoft.com/products/dvd/Free-Video-to-JPG-Converter.htm] . After the splitting process, I get 531 photos. My question is how can I sure of the times of the photos?

Code Select Expand

exiftool -ee -c "%.7f" -gps* -time:all 1.MP4

start time: 10:02:53
finish time: 10:20:24

[Phil Harvey]

I don't have a GoPro Hero 7 video handy right now.  Do you see a SampleTime tag when you extract the GPS?  If so, this tells you the time from the start of the video that is associated with each GPS sample.

- Phil

[Phil Harvey]

OK.  I dug up a Hero 7 sample.  It stores SampleTime and GPSDatetime, but then stores 18 GPS latitude/longitude positions for each sample, and only stores one GPSDateTime for the lot.  The SampleTime starts at 0 and advances by almost exactly 1 second per sample, but the GPSDateTime doesn't advance by exactly 1 second.  It can be different by up to 0.1 seconds or so.

Code Select Expand

> exiftool ../pics/GoProHERO7Black.mp4 -ee -G3 -sampletime -gpsdatetime
[Doc1]          Sample Time                     : 0 s
[Doc2]          Sample Time                     : 1.00 s
[Doc3]          Sample Time                     : 2.00 s
[Doc4]          Sample Time                     : 3.00 s
[Doc5]          Sample Time                     : 4.00 s
[Doc6]          Sample Time                     : 5.00 s
[Doc7]          Sample Time                     : 6.01 s
[Doc8]          Sample Time                     : 7.01 s
[Doc9]          Sample Time                     : 8.01 s
[Doc10]         Sample Time                     : 9.01 s
[Doc11]         Sample Time                     : 10.01 s
[Doc12]         Sample Time                     : 11.01 s
[Doc13]         Sample Time                     : 0 s
[Doc1]          GPS Date Time                   : 2018:09:16 18:01:39.009
[Doc2]          GPS Date Time                   : 2018:09:16 18:01:40.054
[Doc3]          GPS Date Time                   : 2018:09:16 18:01:41.099
[Doc4]          GPS Date Time                   : 2018:09:16 18:01:42.089
[Doc5]          GPS Date Time                   : 2018:09:16 18:01:43.079
[Doc6]          GPS Date Time                   : 2018:09:16 18:01:44.069
[Doc7]          GPS Date Time                   : 2018:09:16 18:01:45.114
[Doc8]          GPS Date Time                   : 2018:09:16 18:01:46.104
[Doc9]          GPS Date Time                   : 2018:09:16 18:01:47.094
[Doc10]         GPS Date Time                   : 2018:09:16 18:01:48.084
[Doc11]         GPS Date Time                   : 2018:09:16 18:01:49.074
[Doc12]         GPS Date Time                   : 2018:09:16 18:01:50.064

Also, I don't know why it stores only 1 GPSDateTime for every 18 GPSLatitude/Longitude positions, especially since there seems to be significant jitter in the GPSDateTime.

So I think you will have to do some testing on your own to figure out how the GPS positions relate to the frames in your video.

If the GoPro software displays GPS position, maybe this is the easiest way to figure it out.  If you find the answer, please tell us because it may help someone else.

- Phil