Hiccuping MPEG-2

Stuart Robinson wrote on 7/4/2006, 9:27 PM
Folks, I seem to be having a few issues when working with MPEG-2 files. As footage is sometimes sent to me in this format I was hoping I could work with the native files and not convert everything to .AVI first. Here's what I'm seeing;

If a clip is opened in the trimmer and played back, every time the trimmer generates a new thumbnail in the timeline as it scrolls, both it and the preview pause for a few frames, then when the video returns it is slightly out of sync with the audio for a moment or two.

The more the trimmer display is zoomed, the more hiccups as it has to generate more thumbnails. Zoomed in to frame level, the preview is stuttering to the point of being unusable.

I also note that if a clip is split, joined as part of a project then a transition applied, that doesn't display correctly in the preview window either, Vegas tends to "jump" across the transition and one can only see it in action if played back a frame at a time.

You're probably going to ask whether my hardware is up to the job, well it should be. ;-) I'm running XP x64 with a pair of dual-core AMD Opteron 280 processors and 4Gb of RAM.

Any ideas? .AVI files (various CODECs) seem fine. Thanks!

Comments

Spot|DSE wrote on 7/4/2006, 9:36 PM
You've already more or less answered your own question; it's about the buffering. Your system is optimized, but Vegas isn't optimized for MPEG editing at this point in time. The trimmer isn't buffered, so it will stutter even more as the file is decoded.
Several things need to occur as you edit mpeg:
Needs to buffer/decode the file
needs to write temp new file for transitions, etc. If off an I-frame, it has to interpolate. (highly likely most of the time)
Needs to convert the file to DV for external or internal preview.

In short, Vegas isn't the best choice if you're editing native mpeg and needed full speed/full frame playback. Additionally, Vegas will always recompress MPEG for output.
TheHappyFriar wrote on 7/4/2006, 9:36 PM
you're working iwth higly compressed files, no less should be expected. :) If you don't want to wait for the pauses then render out to DV AVI.

But.... odds are the Hard drive would be the culperate here, IF something is lacking (which I doubt).
Serena wrote on 7/4/2006, 9:38 PM
Generally it isn't economical to edit m2t clips and the most recent discussion on this can be read at m2t
although DSE conceded that he does sometimes on very short projects when urgent. The time taken to generate the intermediates isn't significant relative to project time.
Stuart Robinson wrote on 7/5/2006, 12:29 PM
Thank you everyone for the helpful replies. I'm sorry I didn't mentioned the storage used as that could indeed be a bottleneck. I have an LSI MegaRaid 300-8X SATA raid controller which promises 3GB/s transfer rates and a pair of Hitachi Deskstar 7K500 set to SATA-II mode. I'm getting excellent benchmarks from this combination.

I realise Vegas isn't the best MPEG editing tool and everything has to be recompressed (why-oh-why!?) but do need to work with MPEG files at times so was hoping for smooth playback at least.

I can do trims and joins in VideoReDo without recompressing, but where the MPEG needs to be used as a project source, would it be best transferred to .AVI first? In which case, which CODEC would folks suggest, given that we're working with a lossy format to begin with?
Serena wrote on 7/5/2006, 3:51 PM
Well, Vegas 6 includes the Cineform codec, but my own preference is to get the full works ($199) from cineform with the extra facilities that provides. This produces lossless intermediates (or near enough using "medium") and very much more pleasant and productive editing experience. Of course you get a far superior end product compared to re-rendering m2t.
fldave wrote on 7/5/2006, 6:06 PM
Serena,

"Of course you get a far superior end product compared to re-rendering m2t"

Not to doubt your statement, but is this really true in your experience? I find it hard to believe that m2t-->cineform-->m2t is far superior to m2t-->m2t. Does the Cineform HD product add that much above the codec to account for the quality?

Sorry, I'm fairly low budget here:)
Stuart Robinson wrote on 7/5/2006, 7:03 PM
Just to be clear, I'm not working with high-definition video, just standard 720×576 (and sometimes 704×576) PAL.

So with that in mind, what is your workflow for creating intermediates?

Can you clarify one other thing; let's say we start with an MPEG-2 clip, perform a basic edit and then save it back to MPEG-2, are you saying that if you take the original clip, create an intermediate, edit that and save it back to MPEG-2 the results will be better?
fldave wrote on 7/5/2006, 7:15 PM
Stuart,
MPEG-2 SD to MPEG-2 SD will always result in quality loss, if it is re-encoded. HD m2t is not as noticeable due to the shear size, but there is a smal loss. Some editors can effectively seam together MPEG-2 without quality loss. Vegas re-encodes the timeline, so expect some loss.

Using vegas, your intermediate can be a 1-1 size ratio. Create an avi the same size and length as your original mpeg clip. Use that on the timeline for editing, it will be much more responsive on the timeline. Right before final rendering, right click the avi in the media pool, select Replace. Select the original mpeg-2 file for the replacement. Render/encode from there.

Serena wrote on 7/5/2006, 9:44 PM
>>m2t -> m2t? Does the Cineform HD product add that much above the codec to account for the quality?


OK, guess we're talking different scenarios. When someone talks about editing m2t files I just presume they mean HDV. However I can say from my first experience of DV (when I mistakenly thought that getting getting tapes captured to DVD would be the way to go) I very quickly discovered that re-rendering produced a much worse result. So I started again, hired a DV camera and captured the tapes afresh as avi. Now if you only copy m2t to m2t then no recompression is involved and the quality is the same. However if you apply any effects, colour correction etc then the stuff has to be rendered again. I haven't yet had a video project where I merely cut the material.
TheHappyFriar wrote on 7/5/2006, 10:15 PM
i've converted mpeg-2 to DV & then the DV to mpeg-2 (for DVD) and the loss was minimal. I normally raise the bitrate a little higher then the origional though, to (hopefully) keep it as "origional" as possible. I'd turn off the thumbnails in the options/prefences, then drop/drag all my mpeg2's to the timeline, setup regions & batch render them all. I'd skip the peak generation too.
farss wrote on 7/6/2006, 2:09 AM
Vegas will always re-encode mpeg-2, even if you do nothing to it.
The internal pipeline is uncompressed digital video, so the mpeg-2 stream is going to be decoded and encoded and possibly due to differences between how the encoder that encoded the file in the first place and the encoder used for the output work there may well be losses although I suspect they'd be pretty minor.

Your very best bet in my opinion is to render to the Sony YUV codec for editing. You have a large fast disk system so the file size and datarate should not be an issue. Assuming you're working with NTSC this would avoid the resampling of going from 4:2:0 to 4:1:1 and then back to 4:2:0. With my suggestion the flow is 4:2:0 to 4:2:2 to 4:2:0, hopefully less room for error.

Bob.