On Sunday 04 December 2005 17:02, Kevin Atkinson wrote:
> Hans Verkuil wrote:
> > On Sunday 04 December 2005 00:58, Kevin Atkinson wrote:
> >>When playing back an mpeg with encoded VBI data the closed caption
> >>are displaying 1-2 seconds too early. This time seams to
> >> correspond with the encoding delay. Also the pack headers before
> >> each VBI packet are bogus: the System Clock Reference is always
> >> 36036 and the mux rate is not the same as the other pack headers.
> >>
> >>From reading the ivtv-devel this seams like a known problem which
> >>isn't fixed because the developer didn't have an NTSC system.
> >> Thus, I am more than willing to work with anyone to fix this
> >> problem. I am a competent programmer myself so if someone can
> >> point me in the right direction I am willing to take a stab at
> >> fixing it myself.
> >
> > Great! It is indeed something that I cannot test myself as PAL
> > doesn't have CC. The delay can be caused by the encoding, the
> > decoding or both.
>
> I have not studied the code in detail, but here is my guess on what
> is going wrong.
>
> My guess is that it is due to the encoder. You start getting VBI
> data immenetly but there is a short (1-2 seconds) delay before you
> start getting MPEG data, so you drop the some VBI packets. This
> causes the VBI data to be displayed 1-2 seconds early since the VBI
> data is real time while the MPEG data is delayed. The correct action
> would be to delay the VBI packets instead of dropping them. Does
> this make sense, and are my assumptions correct?
Yes, it makes sense, I just cannot prove or fix it from PAL country.
Hans
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