[xine-devel] Field based vs frame based interlacing.

[<th...@sh...>]

Hi!

I have a question about the YUV420 chrominance field of an interlaced 
picture.

Consider a picture where the top field lines are red and the bottom 
field lines are green.

If this image was coded in mpeg2 in an interlaced field fashion (As an 
I-P pair) all would be well, The fields would be separate images all red 
and all green.

However if they are mixed together in a frame format, as is done for 
interlaced streams by the libmpeg2 decoder and some hardware decoders, 
what would happen to the picture as the chroma field is subsampled 2 by 
2? Would the colors mix and both fields turn yellow or how are the 
colors distinguished between the two fields?

If anybody could shed some light on this I'd be thankful.

/Thomas