Unai.VITC

Unai.VITC is a simple VITC (vertical interval timecode) signal generator, written in C# for .NET 6.0.

Usage

Unai.VITC is a console application: you must use it through a terminal and control how it works by passing arguments to it (like changing the framerate; see below).

If no arguments are specified, the program's default behaviour will write the result on the console's standard output as a raw bitmap stream, resolution 90x2 and 8-bit grayscale pixel format. It will default to a 25 FPS progresive video and will render indefinitely. Also, you will get a bunch of gibberish getting printed on your console, which represent the generated VITC code. Press Ctrl+C on the terminal to stop it.

To save the output to a file, you can redirect it:

Unai.VITC.exe > my-vitc.raw

Or you can also do the same thing using the -o parameter:

Unai.VITC.exe -o my-vitc.raw

Generate a video file

Unai.VITC only generates the raw VITC signal. If you want to take the output and turn it into a video file, you can use FFmpeg. In this case, we can use a simple pipeline to communicate both processes. The command should start like this:

Unai.VITC.exe | ffmpeg.exe -f rawvideo -video_size 90x2 -pixel_format gray -framerate 25 -i - […]

This will make FFmpeg take the VITC raw signal and interpret it like a raw video stream. Now we can finally generate a VITC signal and save it as a video file:

Unai.VITC.exe | ffmpeg.exe -f rawvideo -video_size 90x2 -pixel_format gray -framerate 25 -i - -f mp4 -c:v h264 -pix_fmt yuv420p -vf scale=360:4:flags=neighbor my-vitc.mp4

NOTE: since there are some video codecs that cannot process video streams below n pixels of resolution, you must upscale it. And to avoid a blurry output, make sure it's using nearest neighbor mode when upscaling. Also, make sure you are converting the 8-bit grayscale pixel format to another pixel format if the former is not supported by the output codec (in this case, H.264 uses YUV 4:2:0).

Results

FFmpeg has a video filter called readvitc which allows us to decode VITC lines from a video. All the possible framerates have been tested with this filter, giving the following results:

24 FPS

25 FPS

29.97 FPS

30 FPS

Arguments

-i: input file

It determines the video file/stream that the VITC lines will be stamped on. This does not overwrite the original file. Use -o to specify the output file. If this option is not specified, no base video is used and instead, only the VITC line is rendered on the output file.

-o: output file

It determines the output file where the result will be saved at. Use - (dash) to indicate the standard output of the console. Default: -.

-f: set pixel format

It indicates the pixel format of both input and output video streams. Default: Grayscale8.

Common values are Grayscale8 and R8G8B8 (24-bit RGB).

-s: set frame size

Sets the input and/or output frame size in pixels. Default: 90x2.

-s WxH where:

• W is width.
• H is height.

-fps: set framerate

It allows you to set the frames per second, but the only accepted values are 24, 25, and 30 (29.97). Default: 25.

-fps [24/25/30]

Example: set framerate to 30 (ATSC)

-fps 30

Example: set framerate to 29.97 (NTSC)

-fps 30 -d (see also the -d modifier)

-tc: set initial timecode

It changes the initial timecode. Default: 00:00:00:00.

-tc HH:MM:SS:FF

Example: start timecode at 14:59:00, frame 6

-tc 14:59:00:06

-t: set duration

It determines how long will be the output. Default: indefinitely.

-t HH:MM:SS:FF

Example: only render the first 15 seconds

-t 00:00:15:00

-ev: set an event

You can set an event at a specified time in order to change parameters or variables. EventType must be UserBits, UserBitsClear, and Timecode (case insensitive). Some events may require an additional parameter that must be joined with the EventType field with a = character.

-ev HH:MM:SS:FF EventType=input

UserBits event type

In the VITC signal, there are some reserved bits that can be used to transmit a maximum of 4 custom bytes per frame. Those custom bits are called user bits and can be set at any time with the -ev modifier. To clean the user bits, use UserBitsClear.

UserBitsClear event type

Clears all the user bits. That is, the user bits are filled with zeros.

Timecode event type

It allows you to change the timecode at any time.

Example: set the user bits to "Test" at the beginning

-ev 00:00:00:00 UserBits=Test

Example: change the timecode to 23:00:00:00 when reaching 00:01:00:00

-ev 00:01:00:00 TimeCode=23:00:00:00

-I: interlaced mode

Specifies whether the video is interlaced or not. In the case of being interlaced, the program will generate two VITC lines per frame: one for each field.

-d: Drop-frame mode

Specifies whether use drop-frame time code or not. If 30 FPS video is indicated with this option enabled, then the program will generate a 29.97 FPS VITC instead.

Example with multiple arguments

Create a VITC signal of 10 seconds long. At second 2, set the user bits to "Test" and at second 4, clear them.

Unai.VITC.exe -t 00:00:10:00 -ev 00:00:02:00 UserBits=Test -ev 00:00:04:00 UserBitsClear

Result