What happens if you Deinterlace a Progressive source?

[FallenAngelII]

I've always chosen for Staxrip to Deinterlace my DVD VOBs but now I've run into a problem. Having already encoding a disc off season 6 of The Simpsons, I discovered that they were Progressive and not Interlaced.

So what now? Is the quality diminished in any way if you deinterlace a progressive source? Will I now have to check every single VOB beforehand to see what kind of video they are? Or does deinterlacing already deinterlaced footage just take longer?

[theewizard]

AFAIK

worst case you end up with a half height squished picture

best case , nothing happens as there is nothing to 'de-interlace'

[edDV]

Was this a "PAL" or "NTSC" disc?

A "smart" deinterlacer would avoid the following mistakes.

If PAL it would try to blend fields. This would decrease vertical resolution by 0-50%.

If NTSC it would be pulling fields from different frames and the destruction would be more substantial.

[theewizard]

I discovered that they were Progressive and not Interlaced.

So what now? Is the quality diminished in any way if you deinterlace a progressive source?

AFAIK techincaly you can't deinterlace it, there is no interlacing

yes there are ways to split the frames and make feilds, but a smart encoder will not make extra work doing something that is not needed

[edDV]

I discovered that they were Progressive and not Interlaced.

So what now? Is the quality diminished in any way if you deinterlace a progressive source?

AFAIK techincaly you can't deinterlace it, there is no interlacing

yes there are ways to split the frames and make feilds, but a smart encoder will not make extra work doing something that is not needed

"Technically" progressive is split into odd/even fields for recording to DVD. This is done to make it easy for cheap DVD players to extract the fields for PAL or NTSC composite/S-Video/analog component playback. The burden is placed on more expensive progressive players to reweave the fields.

[jagabo]

"Technically" progressive is split into odd/even fields for recording to DVD. This is done to make it easy for cheap DVD players to extract the fields for PAL or NTSC composite/S-Video/analog component playback. The burden is placed on more expensive progressive players to reweave the fields.

I don't believe this is true. Progressive sources are encoded as progressive frames. The DVD player then pulls fields out of the frames (as instructed by the pulldown flags) to send to an SD TV, one at a time. (This is a rather trival process. All one has to do is change the stride of the video DAC.) Progressive players have the additional ability to send the frames to a progressive TV via another pathway (ie, not via composite, s-video, or RF).

[manono]

Will I now have to check every single VOB beforehand to see what kind of video they are?

You should have been doing this all along. If film sourced, deinterlacing not only takes longer, but also degrades the video if it isn't really interlaced. If Film with 3:2 pulldown flags, you make the D2V using Force Film and encode for 23.976fps with no further filtering (i. e. no deinterlacing). If hard telecined, like lots of animation, you make the D2V with Honor Pulldown Flags and apply an IVTC, something very different from a deinterlace. If you just apply a deinterlacer to that, depending on the deinterlacer used, you'll either get a duplicate frame in every 5 frames, or 2 blended and blurry frames in every 5 frames. You'll be encoding for 29.97fps, rather than for 23.976fps, you'll be encoding 25% more frames than necessary, and wasting valuable bits. Never deinterlace unless the source is interlaced 30fps - shot using interlaced video cameras.

Now, a lot of that applies for NTSC, and as you're in Sweden, maybe you're dealing only with PAL DVDs. If so, then you should know by now that the majority of PAL DVDs are encoded as interlaced, even though the source is really progressive. If the source is progressive, there's no need to deinterlace, as even on progressive material, the effect is to degrade the quality. The only way to know for sure which you have is to examine the frames. And often with PAL material, even if it appears to be interlaced, it may have field shifts, and a simple Telecide (without Decimate) or TFM (without TDecimate) can make it good again. And PAL DVDs sometimes have the additional problem of bad standards conversions, especially with animations, where you get blended fields. Those can be very difficult to work with.

If you don't know how to determine these things, maybe switch to AutoGK which does an analysis of the source before deciding how to treat it.

[FallenAngelII]

I'm using Staxrip to encode the movies into Ipod compatible h.264. Staxrip doesn't tell what kind of video the source is.

[theewizard]

so , download Gspot, and run that on the source before useing staxrip

[manono]

I'm using Staxrip to encode the movies into Ipod compatible h.264. Staxrip doesn't tell what kind of video the source is.

Oh, H.264. Then AutoGK is no good to you. So, examine the frames yourself. Either play them in a player you can pause and turn off any default deinterlacing, or open a VOB in VDubMod or DGIndex. Go to a place with movement. If you don't see any interlacing, it's not interlaced, and you shouldn't apply a deinterlacer.

[FallenAngelII]

Last night I tried leaving the Deinterlace box unchucked when encoding an interlaced source. The x264/mp4 file that it resulted it was deinterlaced o_O.

The only difference seemed to be that it took only half the time to encode as it would take to if I had checked the Deinterlace box.