GMC/deinterlacing

[rjc7394]

When you deinterlace and use general motion compensation at the same time does that pose any conflict during encoding or create bad video? (I'm using avisynth deinterlace plugin and DivX GMC). Seems to me it could.

[unskinnyboy]

No, ofcourse not. Whatever made you think so? Give us more details and maybe we would be able to help you. The 'bad video' could be due to something else altogether. :)

[rjc7394]

They are two different processes analyzing/correcting motion at the same time. Wouldn't that be like two different deinterlace filters analyzing/correcting motion at the same time? Seems like you can only do one at a time.

[unskinnyboy]

To speak about GMC internals would be something only Koepi or other devs are qualified to do, but AFAIK, from a user stand point GMC is for saving bitrate by reducing the average quantizer for a 2-pass encode. More info here (http://ronald.vslcatena.nl/docs/xvidfaq.html#C3f).

Interlacing/Deinterlacing is a different animal altogether and it is important that you read and understand about it. Here (http://www.100fps.com/) is some good read about the subject.

[rjc7394]

I would have to take a course in film to understand all of this. I've been reading about de/interlaced film for hours and hours. I have an engineering degree and this is akin to a course in physics. I have no clue how film is put together. Thanks much for the reply.

[jggimi]

:confused:

Its not film, its video. Film is a bunch of photographs (frames) projected at some speed (fps). 70mm, 35mm, and 16mm are normally projected at 24fps. In that sense, film is progressive, since the full frames are projected, one at a time.

Video, on the otherhand, started out interlaced due to the nature of the display devices and the bandwidth of the broadcast signals.

Video framerates came about due to the power available: In North America, this was 60hz (30 fps), and in Europe, 50hz (25fps). That allowed them to sync the fields easily to the alternating current being supplied.

The US color standard that was adopted was compatible with B/W. To do so, they reduced the framerate by 5% to add chroma information, hence the framerate reduction to the wierd 29.97fps.

Telecining is the process of taking 24fps film and converting it to 29.97fps video. For more on Telecined video, and conducting an Inverse Telecine, see http.doom9.org/ivtc-tut.htm. It includes a discussion for PAL video users who are dealing with bad NTSC->PAL conversions, or bad film->PAL transfers.

EDIT:

AVI files, of course, are designed to be progressive, since PC monitors are progressive displays. There are some who may want interlaced video in their AVIs, due to their displays (such as a video card with a TV OUT connector used with a large TV). In those cases, the content may be encoded as interlaced.

When a codec such as DivX supports that type of encoding (and most MPEG-2 encoders do, for interlaced DVD or SVCD), the encoders treat the top and bottom fields as separate compressions for motion vectors, and other motion compression technologies like GMC.