3 ms·
> “These positions are tracked in frames, a unit representing 1/75th of a second.” The Director frame was 1/75 seconds? That’s a curious choice because it’s no
by pavlov 3y ago
> “These positions are tracked in frames, a unit representing 1/75th of a second.”
The Director frame was 1/75 seconds? That’s a curious choice because it’s not divisible by 30 which was the most common playback rate.
Film-to-video transfers used a 3:2 pulldown pattern to render 24fps source footage onto 60Hz interlaced video. The exact same approach works for displaying 30fps content on Director’s 75fps display clock… But it’s hard to believe anyone loved 3:2 pulldown so much, they’d intentionally build it in.
Maybe it’s an artifact of the CRT era. I recall refresh rates in the 70-100Hz range were typical in Mac and Windows desktops before LCDs (60Hz on a tube is too flickery for office work). Perhaps 75Hz was a Mac standard in the early 1990s, and that’s where Director got it from.
Another theory: maybe the Director designers thought that 30fps video on a desktop CD-ROM was not realistic, and that content would be at 15fps max. Which has a nice 5x multiplier to the 75Hz internal clock.
- alexdbird 3y agoIt means the Red Book CD audio 'frame' was 1/75 of a second. I don't know what Director did.
- helpfulContrib 3y agoRight - is it not the case that this object is tracking Mode 1 CD-ROM physical (i.e. rotational) frames, not audio/video frames? That is .. a Mode 1× CD-ROM drive reads 150/2 = 75 consecutive sectors per second ... 150k/sec transfer rate ..
- pavlov 3y agoThat makes sense, I never knew that. Thanks! Now I wonder where the Audio CD 44.1k sample rate came from. 44,100 divided by 75 is 588 samples per channel. That doesn't seem like a particularly useful number, whereas 48k / 75 is a more appealing 640.
- sp332 3y agoThe audio format was copied from an earlier standard developed for storing sound on video tape. https://stason.org/TULARC/pc/cd-recordable/2-35-Why-44-1KHz-Why-not-48KHz.html https://stason.org/TULARC/pc/cd-recordable/2-35-Why-44-1KHz-...
- kaetemi 3y agoAdd error correction overhead to that weird number.
- pjz 3y agoMy understanding is that 44.1k is to improve error correction. 44100 == 2^2 * 3^2 * 5^2 * 7^2 ... something about vertices of a hypercube.
- aaronharnly 3y agoBased on some googling, it seems like Macromedia Director defaulted to 30 fps but could be customized for all or portions of a piece. eg https://flylib.com/books/en/4.258.1.47/1/ https://flylib.com/books/en/4.258.1.47/1/ I agree 75 would be surprising and I like your speculations!
- deleted 3y ago[deleted]