Question how to extract closed captions from captured TV video

[jimdagys]

Attached is 20 second clip for PBS TV show capture. What software can be used to extract closed captions?

[Cornucopia]

Why do you think this has CC?

From what I can tell, it doesn't. Nothing parsed in MediaInfo, not available in WMP or VLC or Quicktime (though they should have the option if it were available).
File is 656x480.
Many times, the analog VBI is encoded & stored in e.g. a 640x486 file (notice the extra rows - often used for the VBI).
Video stream is Xvid (aka MPEG4-ASP), CC OUGHT to be stored as EIA-608 or EIA-708-formatted text.

Normally, I'd use CCExtractor or some other McPoodle tool. Doesn't look like you have one this time.
Was encoded with Boilsoft...so, not surprised.

Scott

[jimdagys]

I thought all PBS shows had closed captions. The show that I got was 1 hour long. I used Boilsoft to slice out a 20 second clip. I don't think this editing would have eliminated the closed captions. Could the method of capture (or subsequent encoding) preserve/eliminate the closed captions?

[jagabo]

Closed captions in SD analog video is carried on line 21 of the video signal. Some cards capture line 21 and you can see the encoded CC as short flickering horizontal white line segments on a black background at the top of the frame. Your capture card didn't capture that. Or did you crop them away?

Here's one tool that can read the analog CC if the captured video includes line 21:
http://www.pixeltools.com/tech_tip_closed_captioning_line21.html

Another was mentioned in a thread a few months ago.
https://forum.videohelp.com/threads/360543-Extract-captions-from-digitized-VHS-%28DV-AV...=1#post2284185

You can see the CC on the top line of the sample frame in that thread.

[jimdagys]

Well, this particular capture was captured by somebody else, so I don't know what capture method they used. However, for the sake of discussion, I have an official EZcap capture device that I capture from the analogue output of the on-air digital-to-analogue converter. Do you think this method would preserve the closed captions? I suppose I could use the above methods to find out.

[jagabo]

I have an official EZcap capture device that I capture from the analogue output of the on-air digital-to-analogue converter. Do you think this method would preserve the closed captions?

You can just look at the caps. If you see the flickering white line segments at the top of the frame you have line 21. Some devices will capture lines 21 to 500, others 22 to 501. The former will include the CC, the latter not.

[usually_quiet]

Well, this particular capture was captured by somebody else, so I don't know what capture method they used. However, for the sake of discussion, I have an official EZcap capture device that I capture from the analogue output of the on-air digital-to-analogue converter. Do you think this method would preserve the closed captions? I suppose I could use the above methods to find out.

For that to work (at least with CCExtractor), the EZcap's drivers must support closed captions, and its capture software must use a Direct Show MPEG-2 encoder filter that is able to capture closed captions as GOP user data. Not all capture devices and capture software provide those features.

[jagabo]

Yes, some capture drivers decode the CC on line 21 and output them to the CC pin of the capture filter.