Another use for an SRT file

[TriBar]

@Yosuke

Has anyone tried getting video captions using M2P (or Mavic 2 Zoom I believe is the same) with Litchi?

The SRT-files are the same for both Litchi and DJI GO 4.

Here’s the first line (Home point) of a SRT-file flown with the Mavic 2 Pro & Litchi:
(I deleted the coördinates)
1
00:00:00,000 → 00:00:00,033
FrameCnt : 1, DiffTime : 33ms
2023-01-01 14:51:35,198,603
[iso : 110] [shutter : 1/100.0] [fnum : 400] [ev : -0.3] [ct : 5600] [color_md : default] [focal_len : 280] [latitude : 00.000000] [longtitude : 0.000000] [altitude: 44.130001]

The corresponding first line of the CSV flightlog:

altitude(m)__ 0.40
ultrasonicHeight(m)__ 0.40
pressure[Pa]__ 0
altitudeRaw__ 4.0

[wesbarris]

@Yosuke

I have a client who’s looking to buy videos with video captions of the drone flying 115m above the ground. It would be easy if I could have the video caption written with AGL instead of the other altitude, which seems to be durable from what I’ve been reading here.

Give my “AirData to SRT” converter a try.

[Yosuke]

I’ve been trying to comfort the SRT file produced but the problems are:

1. Since AirData to SRT uses the flight record, it does not apparently sync with videos stored in M2P
2. The minimum unit of time in AirData to SRT is 1 second, which is much smaller in case of the SRT files produced by DJI Go (it has 0.033 sec per line when it’s 30 fps video)
3. It does not include the date and time
4. It does not include the camera settings (ISO, SS, f-stop, ev)

AirData exports log files using GMT to display the time (while my SRT files use my local timezone GMT+13) and I am unable to match it with my SRT files.

So there are so many issues to overcome to switch to the format provided by AirData to SRT. Wish I knew how to modify the SRT files or combine SRT with some data from AirData using some programming languages, but it’s been a pain…

[wesbarris]

That converter is something I just wrote the other day. If you are willing to work with me on this I can solve some of the things you mention but not all. I can make the time interval be whatever you want it to be. The date and time are in the log, so those can be added. Camera settings are not in the log so those can’t be added.

If you want to pursue this, send me a private message and we’ll move this conversation there.

[wesbarris]

I’ve made some updates to my new “AirData to SRT” converter.

1. I found how to detect video capture from within the log file. My converter now only converts the log segments where video was recorded. This makes it much easier to line up the SRT file with the video.
2. I’ve changed the interval selection so that it can be set down to 0.5 seconds.
3. I’ve added local date and time.

[Yosuke]

You are awesome. It’s nearly perfect except that it does not include the camera settings (ISO, shutter speed, f-stop, ev) Is it possible to read and include these? Or are they only stored in the camera’s SRT?

[wesbarris]

@Yosuke

It’s nearly perfect except that it does not include the camera settings (ISO, shutter speed, f-stop, ev) Is it possible to read and include these? Or are they only stored in the camera’s SRT?

I checked, and the camera settings are not in either the AirData nor the Litchi log files. My program was written to read either of those two files so it appears that I do have access to the camera settings from the logs. I can easily modify my program to grab anything you need from the AirData or Litch CSV files but if it is not there, I can’t grab it.

One option would be to merge data from two separate SRT files into one. However, that method presents other problems.

My suggestion is to look into an application called “DashWare”. That program uses the encrypted log files to overlay telemetry data onto your video. Through the encrypted log files, it has access to more data including the camera settings. However, it is a bit more complicated to use. There are YouTube videos on it and also threads about it on MavicPilots. You might want to do a search on that site.