Frame Type vs Frame Structure

[Cyberia]

I don't understand the difference between these things.

I have a PAL vob that is listed as:
frame type=interlaced
frame structure=frames

Could someone elaborate on the distinction between them?

[TEB]

AFAIK, there are 2 ways of coding a Picture, Field based og Frame based, those can be in a interlaced form or progressive form.. Dont ask me why.. thats what i have read..

[Cyberia]

but how can it be interlaced and frame based?

[neuron2]

"Frame type" is used to declare the frame as having been sampled progressively (both the fields at one instant) or interlaced (fields at different moments). Typically, it is used to determine the upsampling that should be done if required. But it's not always accurately used.

"Picture structure" declares whether each MPEG2 encoded "picture" is a full frame or a field. It has to be accurately used, otherwise the picture can't be decoded.

It would make sense to encode interlaced frames with field picture structure, but it is not required. The result is that the combing appears as detail that must be encoded. But on the other hand, there is less overhead for picture headers, decoding, etc.

Don

[Cyberia]

Ok I understand that better.

So in my example, the type is Interlaced but there are no combing artifacts visible. I have seen this before for PAL, is it common for PAL to be Interlaced but not really interlaced?

[neuron2]

It probably means they just accepted the default of their encoder, being totally ignorant of upsampling issues.:(