There are a lot of possible causes and solutions for
video stutters or glitches in playback. Let's see if
we can more or less randomly pierce the veil of mystery
on this subject for you:
-
Use of odd framelengths for FlyerStills or video
clips.
The Flyer works entirely on the color-frame, which
is composed of four fields of video, or two regular
frames. When you set in and out points using the
sliders or the arrow gadgets on the control panel,
you are automatically moving in color-frame increments.
If you type in the in and out-points, you may inadvertently
split a color frame at the start or end of the
edit. The Oz routine FixJitter will analyze a sequence
that is having problems, and will reset in and
out points to eliminate split color-frames.
-
Sequence uses several digital-on effects in a
row, or several digital-off effects in a row.
Here is the long explanation (quoted from documentation):
In order to perform digital effects such as the
kind where the entire picture image is flown off
screen the Toaster must convert the incoming video
signal to a digital display, then fly this "digitized" version
of the video off the screen. The digital version
of the incoming video is in fact slightly behind
the original incoming video, delayed by 1/30th
of a second.
There are essentially two types of digital effects:
(1) those that fly digitized video off the screen
(revealing the preview video source in the background),
and (2) those that fly digitized video on the screen
(covering up the current video source). We call
these digital on" and "digital off" effects.
The Toaster has only one digital channel, so the
digital signal may be on either the Main bus or
the Preview bus at any given time. If the digital
channel is routed through one bus when your sequence
calls for a digital effect on the other bus, the
Switcher must instantaneously switch the digital
channel the moment before the effect can run. This
switch is instantaneous, but the fact that the
video signal has now jumped in time (by 1/30th
of a second) causes the alert viewer to see a stutter
in the video signal.
In live video production situations, you can exercise
a degree of control over which bus (main or preview)
is the current "digital bus" by correct
operation of the Switcher alone (using a combination
of the bus buttons and the Freeze/Live buttons).
You can also choose the type of digital effect
that makes the best use of the current location
of the digital channel (i.e., a "digital on" effect
when the preview bus is digital, or a "digital
off" effect when the main bus is digital).
When sequencing video projects with the Flyer,
this can be a bit tougher.
You'll need to pay attention to your use of digital
effects when editing a project (this means all
of the effects in the Digital and Trajectories
folders). If you do wish to use them, try to make
use of them in the following ways:
When you use a "digital on" effect to
bring a clip to the screen, take the same clip
off the screen with a "digital off" effect.
This lets you avoid a stutter. After using a "digital
on" effect for one video clip, allow another
video clip to occur (using any type of transition
other than a digital one) before using another "digital
on" effect. The switch from the digital clip
to the non digital one will turn the digital channel
back off, so that you can use another "digital
on" effect without danger of stutter. (Avoid
back-to-back "digital on" effects, however.)
Avoid the use of "digital off" effects
with video clips. Only use "digital off" effects
with Flyer Stills and Framestores. Currently, there
is no way to set the main bus to its digital state
in preparation for a "digital off" effect
(except by using a "digital on" effect).
-
Clip or still is on too short a time for next
effect to load.
This will usually produce an error message in
4.1 version Flyer software, but often produced
a glitch in earlier versions, with no resulting
error message. You need to either shorten the duration
of the effect, or lengthen the clip or still ahead
of the effect.
Note: The speed of your Amiga
drive controller and your Amiga system hard drive
are important factors in the loading time of effects.
With faster loading times, you can get away with
shorter clip or still segments in a sequence. With
a slow drive and controller, you will be restricted
in how short a time you can display a clip or still
and be able to use a transition effect, as opposed
to a cut.
-
Noise on the SCSI bus.
This will cause the Flyer to have to make several
attempts at loading the data in order to get a
successful load. The Flyer will redisplay earlier
data when this happens, causing material to appear
out of sequence.
Causes of noise can be bad cabling, bad connectors,
or ground loops in the equipment in the video suite.
Thoroughly check cabling, and eliminate any ground
loops. See also: Ground Loops.
-
Project is accessing directories which exceed
the current limitation of about 180 files in a
Flyer drive directory.
This is a known bug which the product team is working
to resolve. The workaround is to divide project
materials into folders such that no folder contains
more than about 150 files.
This can also produce audio stuttering, even when
it is the video drives which have the overloaded
directories. Project elements may also be displayed
out of sequence.
-
A clip may be corrupt.
Corrupt clips may induce stuttering in project
playback, and the stuttering may not appear at
the corrupt clip, but rather may show up later
in the project sequence.
A corrupt video clip will usually be detectable
if you use the in and out point sliders to scrub
through the clip. An entire field may be missing
or damaged (chroma is missing, or the field is
just noise, or just a portion may show a fault
(a horizontal bar where chroma is missing, or noise
has replaced the image). Such a clip must be deleted
from the drive, and redigitized from the original
source footage.
The file system on a Flyer drive may also go corrupt,
and if so, the drive must be reformatted. Keep
clips only if you are completely certain they are
not corrupt. When in doubt, delete, because one
corrupt clip can corrupt the entire drive. If all
other potential problems have been eliminated,
and you have a sequence which displays video stills
or clips, or even more peculiar, segments of the
video clips used, out of order and in seemingly
random fashion, then it is likely that one of the
Flyer drives has a corrupt file structure.
Note: if the audio "clips" during
recording (exceeds the acceptable input volume
level, as shown in the level meters on the Record
panel), the resulting audio or video clip is actually
corrupt, and must be deleted and redigitized. This
may not produce a visible or easily audible defect
in the resulting video or audio clip, but will
cause problems in project playback, in both video
and audio. You must watch the audio level meters
when recording, and make sure that the clipping
indicator never lights up.
-
Drive fails to transfer data at the rate required
by the video clip.
This is usually detected by the Flyer in the current
version software, but some earlier versions did
not detect it. The causes may be:
-
a long idle time due to a thermal calibration
(T-Cal) or other drive problem. Drives should
be re-tested periodically to see that idle
times, which can be an early trouble indicator,
remain within acceptable Flyer performance
tolerances. Statistically, even a drive that
operates well within tolerance can occasionally
have a long timeout. When this happens, just
retry the recording;
-
the user recorded in a mode the drive cannot
support, i.e. the drive is only capable of
standard mode recording, and the user has attempted
to record in HQ5. The clip must be re-digitized
in the proper mode.
-
the clip was recorded to a portion of the
drive which does not support the required data
transfer rate. This will happen if the drive
was not short-stroked for the highest recording
mode which the user requires. Note that if
the drive is not short-stroked, then a clip
may be directly playable, but will not work
in a sequence because the A/V temp file created
for a transition at either end of the clip
has been written to an area of the drive which
cannot transfer data at the required rate.
Note: for fast sequences, on
drives that have not been short-stroked, if you
arrange the clips on the drives so that clips adjacent
in the sequence are always on opposite drives,
then you eliminate the need for temp files stored
on the slower tracks on the drive. You will be
able to play sequences which you could not play
if temp files were required.
-
The audio or video drives are operating at too
hot a temperature, and are not performing up to
specifications.
Many end users have reported that improving the
cooling of their audio and video drives has corrected
stuttering and glitching in the audio and video.
