Guidance while adding Closed Caption (CEA-708) support

Edward Hervey bilboed at
Fri Jul 5 01:38:13 PDT 2013


  You might want to check also

On Wed, 2013-07-03 at 10:22 -0600, Steve Maynard wrote:
> The group I'm working with has created an element that accepts MPEG
> user data on its sink pad and dissects and compiles that data into
> CEA-708 CC packets/commands and further digests this information into
> WebVTT(text/vtt) output on its source pad.

  It would make more sense to handle this at the (existing) parser

> During development I created a bin with a tee and queues that
> processed in parallel with mpegtsdemux and generated the MPEG user
> data output with a new mime-type of video/user-data.  The new CC
> element auto plugged to this output and all was well.  In an attempt
> to move this code closer to something acceptable to the GStreamer
> community, I have moved the CC element down into plugins-bad and I had
> thought I would patch mpegtsdemux to add a new source pad, however
> mpegtsdemux does not dig deep enough into the video packets to obtain
> the user data.  It appears that mpegvideoparse however does.  I was
> planning on modifying mpegvparse, but that would violate its purpose
> as a parser (adding another output pad).  (apologies for the
> long-winded set-up for my question)
> Should I modify mpegvparse to add "user data" to its out-bound caps
> and then add another demuxer of-sorts to split out the user data
> stream for the new CC element?  Or is there yet a better way that
> currently eludes me?

  Might want to discuss that on the bug report also.
  *  Having the demuxer handle it feels wrong
  *  Having the parser add a new source pad is tricky

> Thanks,
> Steve Maynard
> -- 
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