> Recently on the mplayer lists the topic of chroma from bttv in 4:2:0 > mode. At least in the past it has been true that since the Bt878 has no > true downsampling 4:2:0 mode that the bttv driver only gives chroma from > the top field. Is this still true? > > Since this is really a hardware limitation of the chip, we really > think that bttv should stop supporting 4:2:0 formats completely, and > instead only provide 4:2:2, since that's all it really supports [1]. It > would make things a lot easier, clearer and more correct. In theory I would agree, but capturing in 422 mode takes quite a bit more resources (memory, processing power). Actually, if you want to encode to mpeg, you will need to convert it to 420 anyway. If your hardware is such that it can marginally capture 420, you can forget capturing 422 altogether (I do have such a case, the computer that has my old bt848 card in it and needs to encode to mpeg2). If you plan to deinterlace the frame, it doesn't matter anymore anyway. It would be better to make the conversion used by the user application, user selectable, so the user can select both low-q 420->420 or hi-q 422->420 software conversion.
