Interlaced Bugs in VirtualDub ?

[Mick]

Hi you all,
it seems that there is a severe misunderstanding what Interlaced is concerned in VirtualDub. "Even Field" is really "Odd Field" and vice versa. The VirtualDub Manual says:

"Field order A causes the top field (even scanlines) to be displayed first. Field order B displays the bottom field (odd scanlines) to be displayed first. It is more common for capture devices to use field order B."

But in reality VirtualDub behaves like this:

"Field order B causes the top field (odd scanlines) to be displayed first. Field order A displays the bottom field (even scanlines) to be displayed first. It is more common for capture devices to use field order B."

I checked this with Microsoft, Adobe, Corel, Avid and many others and they confirmed me the following table:

Field Order A:
Lower Field first
Bottom Field first (BFF)
Even Field first
Even/Odd Field Order
1st Line Bottom

Field Order B:
Upper Field first
Top Field first (TFF)
Odd Field first
Odd/Even Field Order
1st Line Top

I captured a Video using Cedocida version 0.2.3 and wondered, why the Field Order was upside down. Then i used the "Field Delay" Filter (VirtualDub 1.9.11/1.10.4) and everthing was right. The Capture without the Filter played in VirtualDub with "Weave TFF" correct while the Capture with the Filter played correct with "Weave BFF".

I also tested this with the "Reverse" Filter from Donald Graft with the same result. This Problem goes back to the earliest Version of VirtualDub and seems to me that nobody noticed that before so i thought i'll let you know.

Cheers, Mick.

[Gavino]

Perhaps this stems from confusion over whether lines are numbered from 0 (in which case the top line is even) or 1 (in which case it is odd). Which system are you assuming? I believe VirtualDub numbers from 0.

[Mick]

Hi Gavino,
i tested it with a Firewire Capture (DV 720x576, 25 fps) and with the Cedocida DV, MainConcept DV and Adaptec DVC Codecs with the same results. The Firewire Capture from the Sony Cam was captured outside VirtualDub and in my NLE (Premiere Pro, Cinegy MoviePack Pro, Ulead Mediastudio) the Firewire Capture was correct (Lower/Even Field first) while the Capture with the DV Codecs without the "Field Delay" Filter (TFF -> BFF Setting) was jerky and with the "Field Delay" Filter it played fine, in VirtualDub and my NLE's.

I know, "Field 0" is a half Even Line before the "Field 1" (Odd Line) starts. My Capture Devices where connected to a Panasonic S-VHS Recorder and Ulead analysed the Field Order as "Top Field first" and enabling the "Preview Acceleration" with "Weave - Top Field first" was smooth while setting "Weave - Bottom Field first" resulted in jerky Playback.

So, i assume that VirtualDub uses "Line 1 (Odd)" instead of "Line 0" (Half Even Field) and behaves just like all other NLE's. A Friend tested it on a Apple with Final Cut with the same results, DV Capture without the "Field Delay" Filter was jerky and out of Sync while the ones with the "Field Delay" Filter played correct.

In TMPEG (Pegasys) the same: DV Material without the Filter played smooth with "Top Field (Field A)" and jerky with "Bottom Field (Field B)" and vice versa. That's why i assume this is a severe misunderstanding in VirtualDub. It's just curios that nobody noticed this before because it's in all VirtualDub versions and derivates.

Cheers, Mick.