"Stutters" or glitches in video during project playback

Product: Flyer

Platforms: 2000 3000 3000T 4000 4000T

Possible causes and solutions:

1) 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.

2) 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).

3) 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.

4) 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.

5) 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.

6) 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.

7) 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.

8) 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.

See Also: Stutters in Video at Cut Edits