How does DVDRebuilder determine if the source is interlaced or progressive?

[manolito]

I need to use DVDRebuilder to shrink the size of a DVD I authored myself. The source consists of a couple of Jazz concerts captured from TV and reencoded with HCenc (to get rid of the station logo).

The sources are basically interlaced, but I reencoded them using HC's AutoInterlace mode which can switch between progressive and interlaced on a per frame basis.

From the HC manual:
HCenc 026 has an auto-detect mode which will choose the optimal encoding method for each
frame (progressive vs interlaced)

Now each of my source files starts with a progressive intro which of course is encoded by HC as progressive. As a consequence MediaInfo reports the files as progressive.


What will happen when I reencode this source with DVDRebuilder? I suppose that DVDRebuilder is not able to switch between progressive and interlaced per frame like HC. Does it analyze the source only from the first frame in a title set or from the first frame of every VOB file, or does it make this decision from the first frame in every cell?

I suppose that the last case is true. This probably means that I have to treat all my source files with ReStream and flag all frames as interlaced before I feed it to DVDRebuilder, right?

Or is there a way to force DVDRebuilder to encode everything as interlaced?


Cheers
manolito

[jdobbs]

DVD Rebuilder analyzes the original source and records the flags for each frame. Those same flags are reinstated after reencoding. That's the reason DVD-RB keeps a source in the exact same format (like a hybrid source) when other programs can't (without having to resort to transcoding).

So, if the source switched between interlaced and progressive -- so does the output.

[manolito]

I think you missed my point. I am not talking just about the flags, I know that DVDRebuilder reinstates them correctly for each frame.

I am talking about the encoder which gets the command from DVDRebuilder to encode in progressve or interlaced mode. If my source is interlaced and DVDRebuilder issues the command "progressive" to the encoder (because the first frame of the cell is indeed progressive) then the encoder will use progressive settings for the whole cell. In this case the encoded result will look terrible because the encoder used the wrong scan order and the wrong motion estimation method.

It won't help to reinstate the correct flags afterwards. Flagging a progressive encode as interlaced later will NOT make this encode interlaced.


Cheers
manolito

[jdobbs]

A decision has to be made as to whether it is progressive or interlaced for most encoders... so DVD-RB has to choose one or the other. But it is never based on a single frame... it is a consensus of the entire stream. If I remember correctly a stream has to be 90% progressive before it is assumed to be progressive, otherwise it is encoded as interlaced. You usually can encode a progressive frame as interlaced and although you lose some efficiency you won't necessarily lose quality. On the other hand, if you attempt to encode interlaced as progressive it gets a little messier.

I certainly can't agree with your last statement. The flags are essential to everything, especially when you involve RFF and switch between telecined and non-telecined sections -- and flagging a progressive frame as interlaced is no big deal -- it happens all the time. The only difference between a single progressive frame and two interlaced fields is the temporal difference between the fields (that doesn't exist in the progressive frame).

[manolito]

If I remember correctly a stream has to be 90% progressive before it is assumed to be progressive, otherwise it is encoded as interlaced.

This answers my original question, thank you. This means that my HC encoded streams which switch between interlaced and progressive will be considered as interlaced by DVDRebuilder, and this is the desired behavior.

Of course setting the flags correctly is essential, but if my interlaced stream has been wrongly encoded with zigzag scan order then setting the correct flags won't help all that much...


Cheers
manolito