Mac DVD player that can increase playback speed while preserving audio quality?
OK, let’s clear up the technical issue here. DVD audio is not stored as a compressed waveform. If it were, then faster playback would cause higher pitch. DVD audio uses a codec based on the same principle as MP3. Those kinds of codecs take the sound, divide it into brief chunks, and run those through a Fourier transform. What gets stored is the coefficients for the Fourier series which will reproduce the waveform. Only not quite; they don’t preserve some information, and that’s why the compression is good. Low-amplitude coefficients get dropped, and phase information isn’t preserved, because humans can’t hear that. So the reproduced waveform won’t look anything like the original if fed into an oscilloscope, but will sound the same to us. What programs like WinDVD do in speeded playback is to treat the packets as if they’re describing shorter time periods.
HotPatatta, the sound on a DVD is stored as a frequency spectrum, not as a moving wiggle. In that, it’s entirely different than a CD or an old style LP, both of which did store and reproduce wiggles. A spectrum can be thought of as a three-dimensional plot with time on one axis, frequency on another, and the brightness at any point (on a scale of white to gray to black) indicating the amplitude of that frequency at that point in time. Here’s an example. The sound you hear on DVD playback changes because the spectrum changes over time. But if you change the timebase of the spectrum, it doesn’t cause any of the frequencies to move up or down. It just changes the duration of the sounds. In other words, what you’re doing is to squash or spread the spectrum diagram along the horizontal time axis, without affecting the vertical frequency axis in any way. So it plays faster or slower, but doesn’t shift the frequency.
I’m not helping, but I gotta say I looove the 1.4x playback (with audio) feature on my PVR (a Pioneer 533). Speech is just barely intelligible, so it’s perfect for the languid PBS documentaries that I frequently watch but don’t want to invest the full 55 minutes in. And to confirm the feasibility of it all … Since PVRs/DVRs use precisely the same encoding technology as DVDs, there certainly should be software out there that can do this. All it does is skip frames and play back the unskipped frames normally.
the program automatically adjusts the pitch of the voices Actually, it’s not. When sound speeds up, it becomes higher. You are in fact looking for a program that does adjust pitch. A program like Audacity can do this for sound files (the “Change Tempo without Changing Pitch” effect), but I haven’t seen anything for DVD or video playback. As for the closing half way through: If it really is the middle (or pretty close), it’s possible your drive is having issues switching DVD layers. Someone a few days ago had a comment or question about that problem, but I think they needed to replace the drive.
