Sequencer Interlacing

I’m having a bit of trouble trying to output interlaced video from the VSE.

I’m trying to create mpeg-2 files to go to ntsc dvd, so I want to encode tff, but Blender doesn’t seem to want to do that. It only does bff, regardless of the state of the “Odd” button. Of course, I did activate the “Fields” button first.

I also tried to force the issue by entering “top 1” into the ffmpeg expert window, but it wasn’t recognized and I couldn’t find it in any of the menus, either.

Using Blender 2.46 on both XP and Vista.

Is there a bug here, or am I just missing something?

Thanks.

Odd should toggle even or odd fields rendering. Are you saying that with fields odd on, you get the same frame 1 that you get with fields odd off? They should be off by a scanline.

Regardless of the setting of the button, G-Spot reports the resulting video as being bff.

Maybe G-Spt (sorry never heard of it) is not picking up the render encoding…? or maybe the FFMPEG encoder is not putting the fields option in the place that g-spot expects. I hate codecs, just for the record, as a necessary evil.

Could be. But if I use ffmpeg by itself outside of Blender (since it is alo installed in a different place with another app that I use) I can use the “top 1” command to change the field order and G-spot reports it correctly. I’ve also looked at the output with MediaInfo and it tells me the same thing.
This might be the “maybe I’m missing something” part of the conversation. I thought that having the wrong field order would make motion artifacts worse, and that certainly seems to be the case. I’m capturing with a Pinnacle Video Transfer, which generates interlaced mp4 files at 720x480, 29.97 fps, 2.5Kbps. I then load that into Blender for editing, but the only way I can get anything watchable is to deinterlace the source in the vse and render a progressive file. Of course, that looks fine on the computer, but taking it a standard DVD isn’t so great, and the initial deinterlacing has already cut the quality.
I suppose I could take mpeg-2 out of Blender and interlace it with VirtualDub or something, but that seems like a lot of compresion/decompression cycles and more work than it should be.

You know, I’ve never thought of this question, which is strange because I’ve been doing HD for awhile now, but if the airwave broadcasts in 1080p, not i, ?right? and so a 1080i TV has to downscan I would imagine. So, maybe an HD DVD should be in 1080p?

But yes, you’re not missing anything, for NTSC, you really need the interlacing for a nice motion blur. and if the blur is “reversed” it does look like crap - jumpy. Be sure your DVD authoring software doesnt convert a p to an i for you, although to be technically correct, you want Blender to render the i, since the object position is calculated every 60th of a second. For fielded video, Blender actually has to do twice the number of renders. I rendered out fielded frames to an avi, and Roxio burned me a DVD just fine, but that was before the FFMPEG days. I have not used FFMPEG to render a fielded video, sorry. BUT I would assume its the same principle. Note that Pinnacle, like DV footage, if captured interlaced, is very hard to deal with when masking or compositing, because of those “jaggy” edges.

Yeah, you’re right there are other methods. Just seemed that since Blender could write mpeg-2 files I could use fewer steps andd eliminate conversions.
I still wonder about the behavior of the “Odd” button though. Maybe I’ll try going to an avi instead and see if it makes any difference. I know that by default Blender is set up to do Even fields for PAL, but since I’m working in in NTSC and doing my own builds, is there any easy way to change that default in the source?
Thanks for your advice and patience.

Well, I’ve been able to come up with a workaround for my problem, but it does appear that there’s a bug in either Blender or the version of ffmpeg used with 2.46 on Windows.

It seems that the interlaced mpeg-2 files made with the “Odd” button pressed are not being flagged properly in the elmentary video stream. Analyzers show the files to still be Bottom Field First even though they should Top Field First. As near as I can tell they are indeed tff, but just aren’t flagged properly.

Demuxing the mpeg-2 and re-flagging the video stream (both done using Avanti) takes care of the problem. The new streams can be burned to DVD (I’m using DVDStyler) and they look very good, with none of the motion artifcating I was seeing before.

I prepared a big long post on this, but I doubt too many people really care, so I’m putting up this abbreviated version in case the bug hangs around for awhile and someone else is looking for an answer.

Please do a bug report at the bug tracker! I think its a case where the frames are rendered properly, but like you say something is getting lost in translation to ffmpeg library

Bug report submitted.