[opendtv] Re: HD standards conversion
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 03 Aug 2005 22:10:00 -0400
Manfredi, Albert E wrote:
> For example, from the original MPEG stream, using
> the original interframes and motion vectors,
> recompute interframes to fall correctly on their
> new time slots, and scale the B and P frames for
> the new frame rate as well.
>
> Sounds CPU intensive, but for non-real-time
> conversion this might be doable.
It is doable, though we have to keep in mind the MPEG motion vectors are
optimized for compressibilty and don't always represent the best picture
of real motion. Also they often don't represent accurate motion for all
blocks in a frame.
But I was mostly suggesting there was little reason to convert first to
24 FPS and then use 3:2 pulldown. That is just a way of inserting
duplicate fields to bring the field rate up on progressive material.
And if you have 25p then you can just insert the duplicate fields as
needed without messing up anything else. If the eventual target is an
interlaced display then it is better (less obvious) to insert occasional
fields instead of frames.
The whole process gets more complicated when you start with interlaced
material since each field is in strict time order. So if you add a
bottom field you have to deal with the fact that the next source field
is also a bottom field but you now need a top field, etc. A nice thing
about telecining progressive material is you have 2 fields from the same
moment of time. This means you can choose to display them in either
order, without retrograde motion.
- Tom
> Tom Barry wrote:
>
>
>>I have not worked with that sort of standards
>>conversion but if you had 25 progressive frames
>>(50 fields) and you wanted 60 fields I can't see
>>any reason to slow it down first, just to speed
>>it up with repeated pulldown fields. If you
>>need 10 more fields / second why not just throw
>>them in at appropriate intervals? And leave the
>>audio alone.
>
>
> I think that what Mark is after is something more
> up to date. In an era of MPEG compression, with
> its motion vectors, one would think that frame
> rate conversion could be accomplished in a less
> crude manner than frame repetition followed by
> uneven dropping of frames, or just sending frames
> at the wrong rate on purpose.
>
> For example, from the original MPEG stream, using
> the original interframes and motion vectors,
> recompute interframes to fall correctly on their
> new time slots, and scale the B and P frames for
> the new frame rate as well.
>
> Sounds CPU intensive, but for non-real-time
> conversion this might be doable.
>
> Bert
>
>
>
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