HOW TO: Do Closed Captioning with OnTheAir Video 4

OnTheAir Video 4 supports more ways to add subtitling to your video. Below are the supported formats and requirements.

Requirements

To output Closed Captioning or OP47, you will need:

• a valid license of OnTheAir Video 4, plus the CC option
• a video device that supports to output VANCs (all recent cards that we support and that have a SDI output should work fine, but older models of Blackmagic devices may not support it). Note that for AJA cards, you need to enable VANCs in AJA Control Panel.

Note that we write the CC or OP47 info in the VANC of an SDI output, so this will only work with an SDI output. When using the direct link (for example to send video from one of our playout application to another), the CC or OP47 are preserved.

Supported types

Type	CEA608/708	OP47
Embedded in a QuickTime media file	Supports a QuickTime Closed Captioning track, in CEA608 or CEA708.	Not supported.
Embedded in a MXF media file	Supports a Closed Captioning track in CEA708	VANC packets with DID 0x43/SDID 0x02
Sidecar file	Supports SRT files*. Output in SDI VANC is 608 packaged into 708, not full 708. So formatting and languages will be limited.	Supports SRT and STL file*

* see below how the SRT file must be formatted.

Formatting the SRT file

As explained above, for OnTheAir Video to use a sidecar SRT file, it must be placed in the same folder as the video file, and bear the same name, with the .srt extension.

A SRT file is very easy to create as it's basically a text file, with information of time. Here is how it looks like:

1
00:00:00,980 --> 00:00:03,020
Hello World!

2
00:00:03,610 --> 00:00:06,017
That's a beauty!

There is one strict limitation. The length of the line must be of maximum 34 characters, so if you need to align your text on the right, you must format it this way:

1
00:00:18,220 --> 00:00:20,360
                       Hello World
              Aligned to the right

You can add a few formatting options, such as the color:

1
00:00:00,980 --> 00:00:03,020
<font color="FFFF00">Hello World</font>

Here are the supported colors and their corresponding codes:

• White:     FFFFFF
• Red:        FF0000
• Green:    00FF00
• Yellow:   FFFF00
• Blue:       0000FF
• Purple:   FF00FF
• Cyan:      00FFFF

And you can use the "{\anX}" tag at the beginning of a line to define the position of the subtitling, where you replace the "X" by a digit from 1 to 9 corresponding to the position of the touches on a numeric keypad. (so for example 1 = Bottom Left, 9 = Top Right, etc...):

1
00:00:00,980 --> 00:00:03,020
{\an9}Shown at the top right

And here are the positions and their corresponding tags:

• Bottom Left:           {\an1}
• Bottom Center:      {\an2}
• Bottom Right:        {\an3}
• Middle Left:            {\an4}
• Middle Center:      {\an5}
• Middle Right:         {\an6}
• Top Left:                 {\an7}
• Top Center:           {\an8}
• Top Right:              {\an9}

Supported Characters

In the "NTSC world" (formats using 29.97fps and 30fps), when we output subtitle to SDI, we format it as CEA-608 packaged into CEA-708. This means that not all characters will be supported. When creating your subtitle make sure not to use any special character.

In any case, the best is to test with our free demo version, and see if the characters that you want to use are supported. But here's a non exhaustive list of characters that should be supported:

Alphanumeric Characters:
Capital letters (A-Z)
Lowercase letters (a-z)
Numbers (0-9)

Basic Punctuation:
Period (.)
Comma (,)
Question mark (?)
Exclamation mark (!)
Hyphen (-)
Apostrophe (')

Special Characters:
Ampersand (&)
Pound/Hash (#)
At symbol (@)
Dollar sign ($)
Percent (%)
Asterisk (*)
Plus (+)
Equal (=)
Semi-colon (;)
Colon (:)
Double Quote (")
Left and right parentheses ( () )
Forward slash (/)
Backslash ()
 

Characters Specific to languages:
All French and Spanish characters should be supported. Other languages are not, but this may change, so don't hesitate to run a quick test with our free demo versions to confirm.

Creating files 

You can embed CC tracks in QuickTime or MXF files. There are multiple ways to do this. Editing software have been more and more capable over the years. We have an article that explains the different workflows for closed Captioning (not for OP47): https://softron.zendesk.com/hc/en-us/articles/360017759879

The options to create OP47 are more scarce. You can only embed OP47 in MXF files, not in QuickTime .mov files. But most editing software can export an SRT file that we can then read. So out of all the possibilities, the SRT file is what seems the most flexible, as many software support it, it can also be uploaded to YouTube or other streaming platform, and is easy to edit. But of course you will need to make sure that it always travels with the file.