- Subarrier FM radio - 1 Update
- 60's-vintage motor overload heaters - 1 Update
| isw <isw@witzend.com>: Jun 02 09:55PM -0700 In article <3cd7c0fd-4b5b-416b-8c1b-8433b6458b9c@googlegroups.com>, > head VCR going frame by frame you can see the effect. Two frames would be the > same and then three frames would be the same. And I am probably the only > person in the world who knows they cheated. That's not "cheating"; it's just the standard "two-three pulldown" technique (known as "telecine") that NTSC (but not PAL) used to convert 24 FPS movies to ~30 FPS video. It wasn't frames that were repeated, though; it was fields (a "field" consists of either the odd-numbered lines, or the even-numbered ones). If you numbered fields sequentially, it went 1-1-2-2-2-3-3-4-4-4-5-5-6-6-6- ... Worked pretty well but added a motion artifact known as "judder" because of the irregularity. It did have the advantage of making the sound run at the proper speed (and incidentally make the movie have the "proper" running time). PAL, OTOH, just overcranked the film from 24 to 25 FPS. The audio pitches were slightly too high, people talked slightly faster, and the film was over slightly quicker. The 2-3 pulldown worked quite well for analog TV, but gave the MPEG folks fits until they finally realized what was messing up their encoding efficiency. MPEG encoding is all about finding regularities and exploiting them, but: If you take that field sequence 1-1-2-2-2-3-3-4-4-4-5-5-6-6-6- ... and show it with the associated film frames: 1-1-2-2-2-3-3-4-4-4-5-5-6-6-6- ... A-A-B-B-C-C-D-D-E-E-F-F-G-G-H ... You see that once in a while a frame (e.g. "C") consists of two fields *not* from the same frame, but from adjacent ones. This really messes with the correlation between odd and even lines that makes MPEG work well. Worse, if there is a scene change just at that point, the odd lines and even lines are from totally different images. The MPEG guys finally figured out that the best thing to do was just reverse the whole process (inverse telecine) to get back to 24 "proper" FPS with no irregular pulldown and no split frames, and then encode that. Isaac |
| John Larkin <jjlarkin@highlandtechnology.com>: Jun 02 12:54PM -0700 >nothing more than generate heat which heats up the separate mechanism that >opens N.C. contacts? >Thanks. Measure the resistances! -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com |
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