Importance of Field Order (TTF vs BFF) in Interlaced video?

[SaSi]

Extracting an elementary video stream from a DVD produces an interlaced MPEG-2 stream. So it will either be "Top Field First" or "Bottom Field First", depending on configuration when it was originally telecined and encoded.

If the stream is re-encoded, what is the significance of encoding with the wrong field order? (e.g re-encoding a TTF video with BFF option).

Will playback become jerky or will it just reduce the encoder's ability to make good decisions?

[DJRumpy]

Playback will be jerky. You'll notice it more in high motion scenes.

You should also remove the pulldown flags to return your video to progressive if appilcable.

[SaSi]

I already noticed that (and how to fix). Thanks for the comment.

To avoid such mistakes in the future (they only show up on the standalone DVD player as the PC is too fast to be showing jerkiness) I am using a nice little program (Restream). It's purpose is to "patch" some of the video stream header values, just like DVDPatcher. I have had no use of this particular feature, but it is great for proofing the actual movie parameters, like interlaced or progressive, 16:9 or 4:3 and field order, among other things. Whenever I rip/demultiplex an MPEG-2 stream out of a VOP, I open it with restream, just to check.

I have found the majority of the movies to be Top Field First. I remember someone mentioning that the usual configuration is Bottom Field First. Am I correct?

BTW, I also reaslised another reason for jerky playback. In an older post of mine, I suggested improving compressibility by increasing the number of B-frames replacing P-frames. Although it works - you get better quality - the standalone DVD players have trouble to keep-up with bidirectional prediction required by the increased number of B-frames (my guess) and stop rythmically every half second or so for a few 10ths of a second. The phenomenon is increasingly apparent the more B-frames are added. Therefore I stick with the traditional IPPBPPBPP... sequence.

[I_AM_CANADIAN]

Hey Sasi, interesting comments you've made. I am no expert with this stuff and still constantly trying to find out why something happenned out the way it did. I came upon this problem first last week, try to rip a porn DVD to SVCD. Easy VCD's programming "predicted" it to be Interlace-A, when by trial and error, I found Interlace-B to be better quality (I-A was very jerky!). What I dont really know though, should I be saving it back as Interlace or non-Interlaced? When I did this trial as mentioned above, I couldnt see any noticable difference between IB->I and IB->nonI . Does this make sense?

Any info is worth its weight in gold,
Brennan

[SaSi]

I'm no expert in VCD (actually have done none ), but,

VCD is progressive by nature, so encoding to MPEG-1 for VCD is about converting possibly interlaced video to progressive.

This task is sensitive to identifying sequence order for fields, which in simple terms is: are odd lines first or are there the even lines first?

I am almost certain that chosing the wrong order should have apparently bad results in video quality. Perhaps the same as the jerkyness I experienced.

So, I assume and guess, that the MPEG-1 encoder must know which fields to expect first in the input video, so that the de-interlacing process is done correctly.

Since the above are wild guesses and extrapolation of my MPEG-2 experience and MPEG-1 reading, consider their value equal to their weight in Pig Iron

[alexago]

Where it's possible to find this utility program (Restream)?

Thanks in advance

[DJRumpy]

You can use PullDown for the same thing. It will let you swap the field order on an encoded stream, change the aspect ratio (DAR), etc. There is a new GUI version over at Doom9. Dunno it the GUI version is in the TOOLS section here yet.

You can use Bitrate Viewer to see which field is first in an encoded MPEG. As usual, Sasi is correct. VCD was designed for progressive streams. The benefit, is that you don't have to mess with pulldown. If you rip a dvd, you can leave the stream at 23.976 fps. It is not necessary to add the pulldown flags.

The usual field order is B first. Use Bitrate Viewer (I think it's in the Tools section?) to see what field order your video uses. It reports other useful info as well. AVI support requires you to purchase/register though.

[SaSi]

DJRumpy,

If I remember correctly, it may have been you who told me B field is usually first, in a past discussion about de-interlacing.

I have been checking each m2v since a few days to check field order, and found that all streams so far are Top field first (which I assume translates to A field first).

Is it possible that for PAL Top Field first is used while for NTSC it's the other way round?

[DJRumpy]

Could be. My capture card also places top field first. I'll try and check some incomming MPEG's to see what they are. Maybe someone else who rips more NTSC, or PAL DVD's will clarify...

[DJRumpy]

I did some digging. It appears my DVD's are TOP field first. I'm guessing this is the usual standard. Maybe someone else will also post a confirmation? Someone from PAL land? If in doubt, I would select TOP field, unless you can verify with Bitrate Viewer (in the TOOLS section).

[peterhuh]

hi
i live in Singapore
PAL is being broadcast here

i am not sure whether its TFF or BFF
but whenever i caputre the video with Huappuage card,
and then encoded to MPEG2 with TMPGEnc,
i always select BFF

if i select TFF, my video will be jumpy on my DVD player