The interlacing plot thickens. While I have identified specific problems with frame misalignment in some PAL DVDs, some other DVDs have interlacing problems which are more difficult to diagnose. For example, Twentieth Century Fox has just sent me a number of DVDs from its World Cinema Collection, including Eat Drink Man Woman (Yin shi nan nu). Ang Lee’s last Asian production before moving into the Western movie industry, it’s something I’m looking forward to watching. But look at the two sections of frame I’ve captured here. They are immediately adjacent to each other in frame sequence, with the clean frame followed by the lined one. (To make the interlacing more obvious here, I’ve doubled the size of the picture details so each scan line occupies two vertical pixels of height.)
But that clean frame is the last frame of a sequence of 13 clean frames. The lined one is the first of a sequence of 12 interlaced frames. This sequence seems to continue throughout the movie: 12 dirty, 13 clean, 12 dirty. Of course it has not escaped my notice that 13+12=25, which is the number of PAL frames per second. Perhaps there was some kind of weird conversion process from NTSC source.
And, indeed, there is evidence for this. The Title holding the movie on the DVD is a little over 124 minutes in duration. IMDB reports the movie length as 123 minutes. Normally when transferred to PAL, the switch from 24 frames per second (film frame rate) to 25 fps (PAL frame rate) reduces the movie running time by four per cent. So this movie would run 118 minutes in PAL, not 124 minutes (the additional minute or so of running time on the DVD is in part accounted for a 10 second MGM lion at the start, plus another 17 seconds of MGM and StreamAV logos on the tail).
So it seems that the encoding method preserved the running time (and, incidentally, the absolute frequency spectrum of the sound) at the cost of heavy interlacing for half of each second of video. I suspect that all this has something to do with the source material with which StreamAV was provided. The giveaway: the English subtitles are hard-coded onto the movie (which must be intensely irritating for Mandarin speakers). Given its high quality work on other titles, I can’t imagine StreamAV doing this.
UPDATE (Tuesday, 5 August 2003, 3:24 pm): StreamAV replies:
The artefact is from the NTSC to PAL transfer, and existed on the master we were delivered. There are a few other NTSC to PAL problems in there as well. It basically came down to the distributor having to make a decision about whether to release the product locally or not. They did the best they could with a title that’s not going to sell a lot of copies.