ddmurphy
10th April 1999, 14:31
Bob
I have seen on our message boards, other newsgroups, and letters to the magazine that many editors using NLE systems suffer from jittery playback. It is a subject close to my heart which has taken me nearly a year to sort through the different causes but now I am able to to capture and play back Hi8 material with no jitters and no out of sync audio with projects up to an hour long. So here goes:-
There are several possible causes for jittery playback. Some are due to the computer hardware, some to the camcorder hardware and some to the editing software.
It would appear that most important is the speed of the hard drive to read and write. This can show up as dropped frames on capture and on playback. Even when no frames are lost during capture, playback is not always smooth if the data read rate is not high enough.
I had a problem which showed that the UDMA hard drive was only achieving about 3Mb/s transfer rate for both read and write. The problem was traced to the fact that something had changed the hard disk properties. Although the BIOS was set to UDMA/33, the My Computer details were showing a basic busmaster type drive with no DMA box, instead of a generic type 47, which Windows 98 prefers. After restoring the original configuration it was possible to enable the DMA box. The transfer rate then shot up to 10Mb/sec, more than enough for the miro card at all compressions.
A second cause of jittery play back has been found to be a combination hardware problem between the camcorder and the capture card. Sometimes, if several scenes were captured together then some of scenes would be extremely jerky on playback. If , however, the scenes were captured separately then the problem disappeared. It would appear that the camcorder when shifting from scene to scene was changing the field dominance, the capture card, however, took its information from the first scene. Capturing individual scenes was a time-consuming process, made easier with the KRP edit plug batch capture device. It did, however, solve that problem.
Another less satisfactory solution is to change the field options of a clip to always deinterlace or flicker removal. This takes longer to render and does result in a reduced quality image.
The third cause of jerkiness can be the load on the processor so that it just cannot cope with the data rate requirements. Closing all unnecessary programmes and changing from the Miro internal sound card to the AWE64 solved this problem. Pinnacle recommend using their own sound facilities but no problems appeared using the AWE 64 sound card. Also capturing at a higher compression ratio helps on playback because the processor is not struggling to produce high data rate transfers. The usual tips also apply…defrag the hard disk before capture…close all unnecessary programmes(ctrl/alt/del) …turn the overlay off…turn the display settings down to 800x600x16bits…have no wallpaper or background etc etc.
There is a fourth type of jitteriness which may be due to my own particular camcorder. Occasionally during playback the picture seems to jump up a line or two then go back down again. It would appear like the camcorder has lost field dominance for a frame or two then recovered. This can sometimes overcome by a) recapturing b) trying a higher compression c) cutting out the offending frame d) splitting the clip for a few frames then changing the field options as above. However, mostly this problem goes unnoticed by the casual observer and it is only we fanatical editors, looking at a clip for the umpteenth time notice anything at all!
I have also found a fifth cause of frame jump and this was due to having the audio recording level too high. When I had a great deal of wind noise or a particularly loud noise the picture appeared to jump for a few frames. I found that when the recording level was reduced the problem mostly disappeared. So on those occasions where sound is not necessary I don’t capture sound. On those other occasions where sound is necessary and it is causing frame jumps despite reducing the input level I capture the sound separately and combine them in my editing programme.
I also have gone back to Premiere 4.2 for two reasons. Premiere 5.1 seemed to take longer to render and absorb more of the processors load. Secondly Premiere 4.3 had a tool called 'conform movie' which I always use on my clips as I have noticed that sometimes the capture is not exactly 25fps and this could lead to out of sync over a long project.
One final piece of advice. For Hi8 work it is not necessary to capture at less than an 8:1 compression ratio. I did not observe any improvement in quality at lower values but it did take up more disk space and put a larger load on the processor.
For information my system is:-
PII 400, 128Mb RAM, 2 UDMA/33 EIDE hard drives (8.4,10.1), Windows 98, miro DC30+,1.32 drivers, ATIexpert@work 8Mb graphics card, Adobe Premiere 4.2/5.1. So it is not a low end system, but there are still noticeable processor effects.
By using all the methods indicated above, jittery playback is now no longer a problem…in my case!
Sorry for such a long message but I hope it helps.
Regards
David Murphy
I have seen on our message boards, other newsgroups, and letters to the magazine that many editors using NLE systems suffer from jittery playback. It is a subject close to my heart which has taken me nearly a year to sort through the different causes but now I am able to to capture and play back Hi8 material with no jitters and no out of sync audio with projects up to an hour long. So here goes:-
There are several possible causes for jittery playback. Some are due to the computer hardware, some to the camcorder hardware and some to the editing software.
It would appear that most important is the speed of the hard drive to read and write. This can show up as dropped frames on capture and on playback. Even when no frames are lost during capture, playback is not always smooth if the data read rate is not high enough.
I had a problem which showed that the UDMA hard drive was only achieving about 3Mb/s transfer rate for both read and write. The problem was traced to the fact that something had changed the hard disk properties. Although the BIOS was set to UDMA/33, the My Computer details were showing a basic busmaster type drive with no DMA box, instead of a generic type 47, which Windows 98 prefers. After restoring the original configuration it was possible to enable the DMA box. The transfer rate then shot up to 10Mb/sec, more than enough for the miro card at all compressions.
A second cause of jittery play back has been found to be a combination hardware problem between the camcorder and the capture card. Sometimes, if several scenes were captured together then some of scenes would be extremely jerky on playback. If , however, the scenes were captured separately then the problem disappeared. It would appear that the camcorder when shifting from scene to scene was changing the field dominance, the capture card, however, took its information from the first scene. Capturing individual scenes was a time-consuming process, made easier with the KRP edit plug batch capture device. It did, however, solve that problem.
Another less satisfactory solution is to change the field options of a clip to always deinterlace or flicker removal. This takes longer to render and does result in a reduced quality image.
The third cause of jerkiness can be the load on the processor so that it just cannot cope with the data rate requirements. Closing all unnecessary programmes and changing from the Miro internal sound card to the AWE64 solved this problem. Pinnacle recommend using their own sound facilities but no problems appeared using the AWE 64 sound card. Also capturing at a higher compression ratio helps on playback because the processor is not struggling to produce high data rate transfers. The usual tips also apply…defrag the hard disk before capture…close all unnecessary programmes(ctrl/alt/del) …turn the overlay off…turn the display settings down to 800x600x16bits…have no wallpaper or background etc etc.
There is a fourth type of jitteriness which may be due to my own particular camcorder. Occasionally during playback the picture seems to jump up a line or two then go back down again. It would appear like the camcorder has lost field dominance for a frame or two then recovered. This can sometimes overcome by a) recapturing b) trying a higher compression c) cutting out the offending frame d) splitting the clip for a few frames then changing the field options as above. However, mostly this problem goes unnoticed by the casual observer and it is only we fanatical editors, looking at a clip for the umpteenth time notice anything at all!
I have also found a fifth cause of frame jump and this was due to having the audio recording level too high. When I had a great deal of wind noise or a particularly loud noise the picture appeared to jump for a few frames. I found that when the recording level was reduced the problem mostly disappeared. So on those occasions where sound is not necessary I don’t capture sound. On those other occasions where sound is necessary and it is causing frame jumps despite reducing the input level I capture the sound separately and combine them in my editing programme.
I also have gone back to Premiere 4.2 for two reasons. Premiere 5.1 seemed to take longer to render and absorb more of the processors load. Secondly Premiere 4.3 had a tool called 'conform movie' which I always use on my clips as I have noticed that sometimes the capture is not exactly 25fps and this could lead to out of sync over a long project.
One final piece of advice. For Hi8 work it is not necessary to capture at less than an 8:1 compression ratio. I did not observe any improvement in quality at lower values but it did take up more disk space and put a larger load on the processor.
For information my system is:-
PII 400, 128Mb RAM, 2 UDMA/33 EIDE hard drives (8.4,10.1), Windows 98, miro DC30+,1.32 drivers, ATIexpert@work 8Mb graphics card, Adobe Premiere 4.2/5.1. So it is not a low end system, but there are still noticeable processor effects.
By using all the methods indicated above, jittery playback is now no longer a problem…in my case!
Sorry for such a long message but I hope it helps.
Regards
David Murphy