Playback issues with i7 cpu

Marton wrote on 3/22/2012, 5:03 AM
I edit my videos from TD10 cam. The clips has no effects,
i only want one to playback in reverse. Playback is very jerky
with my i7-2600 cpu (around 1fps) but the processor usage is only 50-60%. Why?
No gpu acceleration is used. I think i7 is strong enough.
I selected a 3 sec part and render to ram, but again the playback is just not smooth! Even from the RAM? :O
I have 8GB and ram preview set to 500MB.
No other programs are running.

Is this some bug?

Comments

Steve Mann wrote on 3/22/2012, 1:11 PM
Not a bug, but this should be expected with temporally compressed footage. Compression assumes forward playback and temporal compression starts with a full frame of data and for the next 16 or 32 frames (depends on the encoding settings) it only saves the changes from the prior frames. Playing in reverse would create a LOT of work for the processor. But since the reverse playback needs to recreate a lot of data, I wouldn't be surprised to see a lot of hard-disk activity. CPU usage is a very poor indicator of performance.

To get good smooth reverse footage, I would render an intermediate uncompressed clip in the forward direction first, then reverse that.
Marton wrote on 3/22/2012, 2:50 PM
Yes, i know a lot about the compression.
But this doesn't explain why RAM preview was jerky!
dxdy wrote on 3/22/2012, 2:56 PM
Over time there have been a lot of discussions about the size of the preview RAM. After the last round, I changed my preview RAM down to 200 and it seemed to speed things up. I know it is counter-intuitive, but smaller seems to be better. I have had it as low as 60 with good results. I am running i7-950 with 12 GB of RAM.
paul_w wrote on 3/22/2012, 3:19 PM
If you use Shift B to RAM preview a selected section of the reversed clip, you should be getting smooth playback. Thats the whole point of RAM previewing problem areas like events with heavy video fx for example.
The RAM preview setting only needs to be as big as you need for the preview length. But when it comes to rendering, reducing RAM preview (in vegas settings) to a lower value like 100-500 will be faster.
If your RAM preview is still jerky after shift B, then something else is going on.
Does reducing the preview monitor resolution help? Instead of BEST FULL, try BEST HALF for example, and work your way down the list until its full fps.
But really you should be able to achieve full fps as BEST FULL after a Shift B.

Edit: just reading your profile system specs, you may want to update those as it looks like you only have 4GB ram etc but you mentioned 8.

Edit 2: i said Shift L - meant shift B, my bad. fixed.
Paul.
Marton wrote on 3/22/2012, 3:58 PM
dxdy: if i leave it at 60MB for example, i can only make a few frames for preview. It's just not enough. Yes, i lower when i start rendering.
But when using for ram preview i usually set to 5-800MB.

Paul: sorry, i installed my new system not so long ago, and forget to update my profile. Now it's done.
I always use Preview (half) quality for preview, editing.
paul_w wrote on 3/22/2012, 4:11 PM
Marton, re-reading your specs now and you should really be getting full fps after the shift B on a section.
I just tested a short clip here on my dual core laptop. Reversed a clip (Canon mov), shift B'd it, and it plays 25 fps (uk here) at full best. So something else is wrong there.
Are you able to get full fps with anything?? playing forwards or whatever..
My only thought at this time would be the GTX210, its probably one of the lowest spec cards on the market, but it still should be good enough to preview at full rate. It doesnt need to do anything - just display.

Paul.
Marton wrote on 3/23/2012, 1:23 AM
Yes, forward playing is ok at full speed, even with some fx!!
I tried once again, with a little smaller part and it worked finally the reverse too. I don't know what happened yesterday.
paul_w wrote on 3/23/2012, 6:58 AM
Well to my mind, the only difference made by reducing the selected length would be the amount of preview RAM used. So if that now works with a smaller selection then it sounds memory related. Maybe 500MB is not enough for your selection length. Make sure when you hit shift B, it really does complete the full length of the preview and not just a part of it.

Anyway, glad its working now.

Paul.