This utility combines OpenTX/Blackbox log files with Betaflight OSD elements and produces a subtitle file with OSD overlay similiar to the the Betaflight/iNav OSD. You can then play your flight video with subtitle OSD elements in a video player like VLC or import them into YouTube. Not all OSD elements are currently supported and some may display differently from Betaflight/iNav.
If you have any issues or improvements you can raise them on the project site osd-subtitles.
You can either import OpenTX telemetry log files or iNav Blackbox log files.
First of all you need to have telemetry enabled for your craft and you need to have logging enabled for your OpenTX transmitter. The best way is to have logging to be enabled on the same switch as the arm switch, that way logging starts and stops with the flight making it easier to combine the video with the subtitles. I recommend to have the log interval to be at least 1 second or lower. Currently only FrSky and Crossfire telemetry have been tested with OpenTX, so other telemetry logs may not work.
You need to convert the Blackbox flight log binary “.TXT file into CSV format before it can be used. This can be done using the iNav Blackbox tools. The resulting CSV file needs to have datetime and GPS data so the conversion must be run using the following command line:
blackbox_decode --datetime --merge-gps LOG00001.TXT
Note that if you use instead the Betaflight Blackbox Log Viewer to export the CSV file instead of the iNav Blackbox tools then the resulting CSV file is missing all GPS information and so therefore the iNav Blackbox tools are a better option.
After the conversion you can use the resulting LOG00001.CSV as input file to the OSD log. Since the original Blackbox data is very large and is being logged every couple of milliseconds, the resulting subtitle file is instead reduced to update the OSD only every 200 ms.
On the main OSD Subtitles page start by selecting the OpenTX/Blackbox log file you want to import by clicking on Open... for the log. When a log file with more than one flight is loaded the individual flights inside the log file are split into different flight logs and displayed in the Flight selection. This only works if the time between different flights is more than 10 seconds. Select which flight you want to generate subtitles for in the selection box. The name of the flight is the start date and the duration of the flight is in parenthesis in min:sec.
Next you can select the CLI dump file for the craft. You can get this information in the CLI by using diff all and then saving it to a text file. This step is not required but loading the correct CLI file will pre fill the values for the OSD elements, Post Flight Statistics, profile, units, position, craft name and display name, otherwise you will have to input them all individually. You can also save and load this information from a config file if you want to have a custom position config different from the CLI file. This is mainly for the Betaflight CLI format but some elements of iNav are also partially supported.
Select what elements you want to use by check marking them for the selected OSD profile number. On the image screen you can change the position of the OSD elements using either the mouse to drag and drop the elements or specify the position directly in the element with X and Y values which are in percentage of the video screen. So for example x=0%, y=0% would be in the upper left corner, x=50%, y=%50 would be in the middle of the screen and x=100%, y=100% would be in the lower right corner of the video. Note that for some players there are extra margins for all subtitles so the subtitles start from the margin instead of the whole screen so that means the position doesn’t always map correctly to screen size.
Select what post flight statistics values you want to show. The Post Flight Statistics will be shown on screen for one minute after the flight has ended.
Select what OSD profile index you want to use for the subtitles. Select the battery cell count of the craft if you display the average battery voltage or you can use Auto which will try to guess the cell count, but this sometimes does not work correctly if the starting voltage in the log is less than maximum cell voltage, in that case select the correct number of cells. If you want to display Craft name and Display name you can input those in the corresponding fields.
The trim start field can be used to trim the start of the log. For example if you have the video start at 30 seconds already into the flight, you would input 30000 in the trim start field to cut out 30 seconds from the start and the corresponding telemetry information.
The trim end field can be used to trim the end of the log. For example if you want to cut the last 10 seconds of the log, you would input 10000 in the trim end field. The trim start and trim end can be combined to trim both from the start and the end at the same time.
The delay field is for adjusting the timing of the subtitles. This can be useful if the OSD information does not start at the same time as the video. Just note how long the delays is when the OSD should start to display in the video and input the delay here. For example if the OSD should start at 5 seconds into the video then input 5000.
There is currently support for SSA, SRT and WebVTT subtitle formats.
SSA format includes positioning, unicode symbols, font and font size. This format can be used for example to burn subtitles into video using FFmpeg. The font name is dependent on what fonts are available on the system, so I would recommend to use any one of these standard fonts: Arial, Arial Black, Tahoma, Times New Roman and Verdana.SRT is a very simple one line text with all values combined. This format does not include any positioning or symbols, but is widely supported.WebVTT format includes positioning and unicode symbols. This format is widely supported for web videos.WebVTT (YouTube) is the same as the WebVTT format but includes different positioning since YouTube doesn’t implement the WebVTT standard correctly.Click on Generate to preview the output or click on Generate and save to save the subtitle file directly to your computer and then add this subtitle file to your flight video.