PAL interlaced at 25 fps?

[dli]

I'm looking at a PAL DVD (Species 3) for which Dgindex determines the following attributes which seem to be contradictory to me:

Frame rate: 25 fps
Video type: PAL
Frame type: interlaced
Frame struct: frame

I see that the frame type/struct contradiction has been addressed previously (http://forum.doom9.org/showthread.php?s=&threadid=88884), however, I fail to understand how PAL at 25 fps can be interlaced. Also I'm not seeing any interlace artefacts in the preview.

Is this a detection bug in Dgindex and is it safe to assume that the content is actually PAL progressive and proceed accordingly?

[neuron2]

DGIndex just reports the state of the MPEG2 flags. There is nothing to stop the DVD authors from doing the MPEG2 encoding as interlaced when the content is really progressive.

[Paulcat]

Also, the framerate has nothing to do with whether the video is interlaced or not, as that seems to be the implication of what you wrote..

[dli]

I see. But hypothetically if frame structure was set to field the framerate would have to be 50 fps for it to be possibly interlaced?

[neuron2]

No. The frame rate is the display frame rate, not the encoded picture rate. For example, the analog PAL sent to the TV is really 50 fields per second, but we call it 25 frames per second.

If you are interested, the MPEG2 specifications are available in the Library at my web site. You can investigate the meaning and interpretation of the terms and flags there.