Posted by Jukka Aho on 12/11/06 13:50

Citizen Bob wrote:

>> Note that if your original material was shot in interlaced format,
>> with an interlacing video camera (home video is usually like this)
>> you have just lost half of the temporal resolution. All motion will
>> be twice as juddery in the XviD file. (Converting interlaced video
>> from 720×480 to 720×400 implies deinterlacing, which typically
>> causes this kind of effect - unless the frame rate is upped to the
>> field rate in the conversion, which most people don't even think of
>> doing.)

> I am sure you can find examples that support your claim, just as I can
> find examples that do not support your claim.

My "claim" (I would rather call it a simple statement of a fact, since
that what it is) only concerned interlaced video, shot with an
interlacing video camera. I challenge you to find examples of interlaced
video, shot with an interlacing video camera, that "do not support my
claim". :)

> The source I used in the tests I provides was from a standard
> DVD.

Just saying it was "a standard DVD" does not indicate whether it
contains this type of material or not. A standard DVD might contain
interlaced material (shot with an interlacing video camera) or it might
not contain that kind of material. It depends on how the material was
originally shot and post-processed, not on the fact that it was stored
on a DVD.

>> You probably can't see the difference on a computer screen, though.
>> Computer video players will usually deinterlace interlaced material
>> on the fly, anyway, so the playback of your original file is
>> compromised as well - on a computer screen. But the difference
>> should be obvious if you make a DVD out of the original material,
>> play it back on a regular tv set, and compare that to the converted
>> material.

> I did exactly that and I could not see any loss of resolution.

Perhaps your source material was not truly interlaced, but progressive
(or film-originated and 3:2-telecined, and Auto Gordian Knot reverted it
back into progressive frames.)

> The newest XviD codecs are really quite good. You sound like you are
> using older codecs.

What I'm talking about has little to do with the codec you use. The main
point here is vertical resizing, which can be disastrous for interlaced
video and will certainly lead to loss of quality. (In the worst case,
severe artifacting [1]; in the less severe cases - when typical
deinterlacing algorithms are being applied - usually loss of half of the
temporal resolution. In other words, loss of motion smoothness.)

Hint: Hollywood movies usually aren't shot with interlacing video
cameras, so if you're into movie piratism, this might not be a big
concern for you. But it is a very real concern for those of us who, for
instance, shoot their own home videos and then want to store them into
formats like XviD.

_____

[1] As you can see from the couple of first pictures on this page:
<http://www.100fps.com/>.

--
znark

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