Re: [Zapping-misc] Using libzvbi to extract captions/XDS from raw caption bytes

[faginbagin <my...@hb...>]

Hi Brian,

On 6/8/2011 7:53 PM, Brian Enigma wrote:
> I have what I believe to be a simple goal that I'd like to achieve
> using libzvbi, but after going through the documentation and
> tinkering with some test code, I am unable to get zvbi to do what I
> need.
>
> Basically, I have VBI bytes as input.  It's not attached to video,
> it's just raw ATSC "line 21" bytes, each one starting with the four
> characters "GA94" and 0x03 and the other assorted header bytes,
> followed by the actual 608/708 triple-byte payloads.  As output, I'd
> like to get callbacks for captions and XDS data so that I can
> programmatically grab the parsed data.  It looks like I should be
> able to just instantiate a decoder (vbi_decoder_new), add an event
> handler (vbi_event_handler_add), then repeatedly throw bytes at it
> (vbi_decode) and get callbacks.  I'm not sure I quite understand the
> vbi_sliced struct.  I've tried loading my raw bytes into the "data"
> field of vbi_sliced (using a couple of different offsets -- including
> the GA94 ATSC header, just after it, starting at the first 608 byte
> triplet, etc.) with no luck.  I also tried vbi_raw_decode to see if
> that will take my raw bytes and package them in a vbi_sliced data
> structure.  So far, I haven't gotten anything to work.
>
> I'd like to try out and step through the example code to see what
> sorts of bytes they are pushing around, but the apps that take file
> inputs seem to want to initialize some /dev device that I don't have,
> even when I just point them to files.  (I don't have any sort of
> special video capture hardware.)
>
> What am I doing wrong and/or what is the correct way to do this?
>
> -Brian

I have an application that does something similar. It uses mythtv's version of ffmpeg to parse ATSC recordings to get at the EIA-608 caption data, then feeds that data to libzvbi. I use libzvbi's support for generating .png files to create images I can later use with dvdauthor's spumux to convert closed captions into DVD subtitles. If this sounds interesting, you can find more details, as well as a link to the source code here:
http://www.hbuus.com/cc2subtitles/

HTH,
Helen