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Univers Mac Interactif 53
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UTILITAIRES IMPORTANTS
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1995-07-07
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This version of Sparkle supports sound in a limited fashion. A sound file can be
associated with an MPEG (or a set of PICTs) and played while the MPEG plays.
The good news is that part of the support I have is completely fleshed out.
You can play sound backwards or forwards, at variable rates, and with random access.
Sound playback is (with the warning about drivers below) continuous even when the
disk is going beserk pulling data in at 16bits/stereo/44.1kHz. I had a vicious
lesson in what can and can't be done with the mac interrupt system while putting
this all together but it now all runs beautifully at interrupt level and I can't
make it crash.
But here are the limitations.
* AIFF, compressed AIFF and .WAV files are supported. Sparkle will first look
for a .AIFF file, if that's unsuccessful for a .AIF file and if that's
unsuccessful, for a .WAV file. If there exist any .MPG/.AU combinations
out there I could support AU if desired. However I have never seen such a combo.
.snd files are not, and will not be supprted. They are only designed to support
short sounds and trying to force the snd format to handle multi-megabyte sounds
is a pointless exercise.
.WAV support requires Sound Manager 3.1.
* Suppose Sparkle is opening a file name.mpg. It will look in the same folder
for a file name.AIFF. If it finds such a file, you'll get audio. If it doesn't
find the file, you'll get no audio. If you are opening a set of pictures
called waves.0, waves.1, etc, then again the audio file must be names waves.AIFF
and must be in the same directory as the picture files.
This probably is relevant to programs that use Sparkle, like Mosaic or Netscape.
I don't know how Mosaic/Netscape cope when they find an MPEG/WAV pair at
a WWW site. If the Mosaic/Netsca[e authors want to contact me to consider
some protocol (apple events or whatever) for handling this, feel free to mail me.
* On my Quadra 610, 8bit mono sound at 11KHz works without a hitch. 16bit stereo sound
at 44.1kHz (sixteen times as much data) works but with a noticable (though
not unbearable) slowing down of the video.
The sound is read in using a funky triple buffering scheme with async IO and
async sound. This works beautifully on my mac's internal hard drive. However
on my Syquest cartridge with the APS 3.05 driver sometimes the sound can stutter.
As far as I can tell this is because the APS driver does very naughty things
like switching off interrupts for long periods of time (at the same time
that the sound stops, the mouse also stops moving briefly).
If anyone has suggestions/comments on the subject, please let me know. My guess
is that the only fix is to get APS to release drivers which don't disable
interrupts for so long.
Also, of course, since we're using async IO, use SCSI Manager 4.3 for better
performance.
* The .WAV sounds I have tried occasionally have jerks in them. These were recorded
in the sound and are not Sparkle's fault. Also the .WAVs I've tried don't
seem to sync very well with the video, like the audio was recorded with a slight
delay relative to the video. Again I can't do much about that.
* There is now a menu item, Set Frame Rate ..., under the Playback menu. This allows
you to set the frame rate of an MPEG/set of PICTs to what you wish. Note that
this only affects video playback, not audio. Note also that when Sparkle opens
an MPEG or PICT set with an associated sound file, the duration of the video
is scaled to match the duration of the audio. Normally this is what one would
want and so you shouldn't need to touch the Set Frame Rate ... option much if you
have associated sound. If you have an MPEG without sound and it appears to play
way too fast, you may want to set the frame rate to something lower.
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What do you do if you want to play back MPEG audio?
I had hoped that a program like Sparkle would spontaneously arise to fill the mac
MPEG audio space. Unfortunately I have been disappointed.
There are three MPEG audio players that I know of:
MPEGAud PPC 1.0a9
MPEG Audio for Macintosh 0.3.2
MPEG/CD 1.05
However it is difficult to get excited about any of these programs.
They're none of them as fast as one would hope---in fairness MPEG audio like video
does require some serious CPU work.
Additionally they all have serious user interface problems.
Considering specifics,
* MPEGAud claims to convert a file to an AIFF file. However it leaves out the common
chunk of the AIFF file and so the AIFF file is invalid and many apps (including
Sparkle) will not be able to read it.
* MPEG Audio for Macintosh outputs snd resource files, not AIFF files. snd files are
very inappropriate for large sound files for two reasons---they are major pain to
play asynchronousl, and they are limited in size to less than 16MB.
* MPEG/CD does actually output a valid AIFF file if you ask it to. However its
user interface can be very confusing.
My recommendation would be to go with MPEG/CD and we can hope it's incrementally
improved as time goes by.
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