> Date: Mon, 18 Jan 2010 19:35:48 +0100
> From: Hans Verkuil <[email protected]>
> - Currently a private 'ivtv' format is used to store VBI data in an MPEG
stream.
> I know that there is a standard format that can be used to store info
like
> this in an MPEG stream and that should make this more compatible.
This would be lovely. The current state of affairs means that doing
any sort of editing (such as removing commercials) loses all CC data,
since the tools that do so don't know to keep them. Only editors that
simply bulk-copy data between cutpoints keep anything, but most seem
to reencode the stream as it goes by (after all, you'd like to allow
cutpoints between GOPs and/or not simply chop half a frame off or
whatever), and thus CC gets tossed. Since I value CC data, this
means I can never edit. (Well, I can hook a 350's output to some
other card's input and do edits in the style of the bad old days
of tape-to-tape realtime editing, but that's not really what one
expects from editing these days... :)
> I
know I
> looked at this in the past, but I decided against it at the time
because the
> total size of the VBI payload could be more than the maximum size
supported
> by the cx23415 MPEG decoder. It's not a problem to write larger
packets, but
> the MPEG hardware decoder will truncate it internally.
> In hindsight I should have gone with the standard anyway since I don't
think
> this will be a problem in practice.
Would it be possible to buffer the data and write any spillover to the
next packet? (Better a late caption than half a caption.) This
assumes that the average rate is low enough that you won't require
indefinitely-large spill, of course. Though if you think that nobody
puts -that- much CC in any source anyway, the complexity wouldn't be
worth it.
If someone makes this change in CC embedding, it would also be
wonderful if ivtv included a tool that could take the old-style,
incompatible stream, and re-embed the CC data in a new stream in the
new, compatible style. This would allow previously-recorded streams
to be editable and would allow flushing out all the old-format data
in an archive all at once.
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