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Video Caption w/Inspire 2 & DJI GO 4
1764 8 2018-3-5
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inspirelwdd
lvl.2

United States
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Through my research I've found that our new Inspire 2 when "Video Caption" is turned on in the DJI GO 4 app, DOES NOT create a separate .SRT file with the MP4. When we did video with our older Inspire 1, "video caption" on created a separate .SRT file with the MP4. We use the .SRT file that captures telemetry data for mapping. What I've discovered using VLC is that when you play an MP4 captured by Inspire 2 and turn on subtitle, you'll see the telemetry data on the bottom of the screen. Has anybody else discovered this? Is anybody using software to extract the subtitle data from the MP4 and creating their own .SRT?
2018-3-5
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DJI Mindy
Administrator
Flight distance : 7 ft
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There is no separate SRT file will be generated for Inspire 2, sorry for the inconvenience caused and appreciate your understanding.
2018-3-7
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inspirelwdd
lvl.2

United States
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I appreciate the response acknowledging that the Inspire 2 does not generate a separate .SRT file when video caption = ON
This is most critical to us for our mapping. Did DJI realize the impact this has on customers who need that telemetry data? Moving on, does DJI have a recommended or suggested methodology for extracting the telemetry data out of an MP4 to a .SRT file?
2018-3-7
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Daroga
Captain
Flight distance : 3517287 ft
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United States
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inspirelwdd Posted at 2018-3-7 03:48
I appreciate the response acknowledging that the Inspire 2 does not generate a separate .SRT file when video caption = ON
This is most critical to us for our mapping. Did DJI realize the impact this has on customers who need that telemetry data? Moving on, does DJI have a recommended or suggested methodology for extracting the telemetry data out of an MP4 to a .SRT file?

Inspire Lake Worth Drainage District - I PM'd you regarding exporting the SRT....

If the SRT is presented as a stream within the MP4 container, then it could be extracted using the FFMPEG tool. I unfortunately don't have a sample Inspire 2 video to evaluate (If you have a sample that could be shared it would be beneficial). If you are interested, I could provide you with a brief write-up on possible SRT export investigation procedures using FFMPEG but will need some background info as FFMPEG is a cmdline/terminal application and specific to the platform running the application (MAC/PC/Linux). This may better be accomplished via email. I've PM'd my email address if you are interested. (Some smartphone browsers don't show DJI forum PM's)
2018-3-7
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inspirelwdd
lvl.2

United States
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First let me say that I do not believe the SRT or telemetry information is a separate stream within the MP4 container. Having said that, extracting subtitle Information from a DJI Inspire 2 MP4 file is not possible. I found through research on another forum that you can have a soft encoded subtitle or a hard encoded subtitle. I believe DJI hard encodes or burns the telemetry in to the MP4 making it impossible to remove the subtitle information (SRT). I have used good applications such as Subtitle Edit and CCExtractor GUI that give you the ability to work with subtitle information. One way or another most applications that you'll find are just a GUI version of FFmpeg which I've also tried. I'm most interested in seeing a response from DJI themselves as to whether telemetry information can be extracted from their MP4 file.
2018-3-7
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Daroga
Captain
Flight distance : 3517287 ft
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United States
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inspirelwdd Posted at 2018-3-7 06:27
First let me say that I do not believe the SRT or telemetry information is a separate stream within the MP4 container. Having said that, extracting subtitle Information from a DJI Inspire 2 MP4 file is not possible. I found through research on another forum that you can have a soft encoded subtitle or a hard encoded subtitle. I believe DJI hard encodes or burns the telemetry in to the MP4 making it impossible to remove the subtitle information (SRT). I have used good applications such as Subtitle Edit and CCExtractor GUI that give you the ability to work with subtitle information. One way or another most applications that you'll find are just a GUI version of FFmpeg which I've also tried. I'm most interested in seeing a response from DJI themselves as to whether telemetry information can be extracted from their MP4 file.

Thanks for sharing your in-depth research.
Was curious if CineCore 2 was just embedding as a separate srt stream.
Unfortunate that they are not!
2018-3-7
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jflyer3
lvl.3
United States
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inspirelwdd Posted at 2018-3-7 06:27
First let me say that I do not believe the SRT or telemetry information is a separate stream within the MP4 container. Having said that, extracting subtitle Information from a DJI Inspire 2 MP4 file is not possible. I found through research on another forum that you can have a soft encoded subtitle or a hard encoded subtitle. I believe DJI hard encodes or burns the telemetry in to the MP4 making it impossible to remove the subtitle information (SRT). I have used good applications such as Subtitle Edit and CCExtractor GUI that give you the ability to work with subtitle information. One way or another most applications that you'll find are just a GUI version of FFmpeg which I've also tried. I'm most interested in seeing a response from DJI themselves as to whether telemetry information can be extracted from their MP4 file.

You may want to check out Dashcam Viewer. It can process SRT files, as well as SRT data embedded in the MP4 file.

Now if we could just convince DJI to increase the precision of the lat/lon data in the SRT file (and add UAS speed), that be great!  This thread has more info.
2018-5-10
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0Kajuna0
Captain
Flight distance : 249606 ft
Spain
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Hi, Could anyone with Inspire 2 footage help me by testing my subtitle extraction tool? https://djitelemetryoverlay.com/subtitle-extractor

Thanks!
2019-11-23
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slimcheney
lvl.1

Italy
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Is there a way to enable GPS timestamps in the subtitle track on an inspire 2?
2020-1-16
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