[mythtv] Keyframe adjust table (posibel bug(s))

[Geoffrey Hausheer]

On Mon, 5 Jan 2004 12:39:48 +0100, "Torbjörn Jansson" said:
> I have found the cause of the problem.
> 
> When directshow does a seek all timestamps on the samples is reset to
> zero,
> so the first video sample shoud be at time zero or prety close.
> When I timestamp the video frames I use the timecode in rtframeheader but
> that field is not updated after a file has been transcoded, so this
> results
> in samples with timestamps from the orginal untranscoded file.
> 
> So as I seek past more and more cutpoints the timestamps drift and
> becomes
> more off and that's why I had to wait about 8-9 minutes yesterday for the
> video to start playing (I cut off 2 comercials of about that lenght)
> 
> So to answer your question "Is it necessary to change the timecodes?" in
> transcode.cpp yes, atleast for the directshow filters.
> 
> I gues I coud modify it so it uses video frame numbers instead of
> timecodes,
> but the question is, what is most accurate? Timecode or framenumbers
> 
Well, from my recent expereinces with MPEG2 (and previous experineces
with my crappy bttv card), I wouldn't recommend seeking based on the pts.
 The pts is best used for a/v syncing, but if the stream is broken, the
pts may not be continuous.  Some mpeg2 editors will cut sections out of a
file, mark the next gop broken, and not update the  pts.  This is
apparently legal.  Of course the nuv used by myth is a custom format, and
we can do what we like, but the pts won't necessarily be continuous there
either (if your card starts dropping frames, the pts can have gaps).

So I would recommend seeking using frame numbers, and syncing with
timestamps.

However, I don't think it would be hard to fix the timestamps.  I didn't
do so before, because I thoughtit might be useful to preserve the orginal
timestamps for some future purpose (also, I didn't have an easy way to
update them).  I don't think it would be too hard to update them now. 
Even still, it'd mean you'd need to have some way to deal with the
current way, since there are (maybe) lots of recordings out there that
have been transcoded.

Let me know what you want me to do.

.Geoff