MPEG2 seems to be one of the best implemented ones. Try XDCAM 1280x720. What frame rate is your project and source?

I've tried most of the possible settings I can think of. The computer handles 100+ audio tracks + the mp4 video with ease, it's just when I switch to surround sound mixing that I end up in trouble and get contast audio dropouts etc. Check for details here on that issue: http://www.sonycreativesoftware.com/forums/showmessage.asp?messageid=937734

Choosing the correct video format is just one step to making it easier for Vegas to run the material. We also need to cut down the number of tracks and effects by doing prerenders if need be before doing 5.1 mix.

The original material is 25fps Prores 422 HQ. Unfortunately it is edited on a mac based system with Premiere Pro so I'm uncertain if it can render XDCAM, hence my suggestion of DNxHD.

XDCAM-ex.MXF in 1080 or 720 will have the least overhead. Alternatives to try would be Cineform-low profile in .AVI, or even rendering a "PAL widescreen" DV bump using a custom profile where you specify progressive 25P. DV is also under the .AVI format selections.

"Alternatives to try would be Cineform-low profile in .AVI,"

Does Cineform handle more than two audio channels these days?

I would agree with others in this thread that XDCAM in MXF (Sony MXF) or MP4 (XDCAM EX) is about as low overhead as it gets. XDCAM is mpeg-2 video.

"Does Cineform handle more than two audio channels these days?"

I was assuming that the user only really needs picture, or picture with 2 channels of audio since he is mixing sound.

I've done several 5.1 mixes with DV AVI back on my old AMD XP 1800. Ran great with multiple audio & video tracks.

DV AVI is the lest intense format out there for the most part.

ESPECIALLY if you are doing 5.1 you need to render a file to play back on a reference player.
NO accurate preview is possible because the audio bus mapper on the timeline and ENCODED COMPRESSED 5.1 are completely different.
It's trial and error, not a one-step product.

+1 TheHappyFriar

DV AVI is intraframe, so there is no temporal compression to decompress. And the Sony DV codec is basically unchanged for over a decade, and played smoothly even on mediocre hardware back then, so it's demands are tiny for modern PCs. It can do widescreen too.

ESPECIALLY if you are doing 5.1 you need to render a file to play back on a reference player.

Accurate preview is possible, you just need to compensate for any delay with the decoder. I was under the impression that the player auto compensates though (at least one DVD player I had let you adjust 5.1 mix settings). When I've done 5.1 mixes & exported to DVD I never recall ANY playback issues and I did nothing fancy with my mixes or encodes.

No, accurate preview of 5.1 to be ENCODED is not possible on the timeline.

Sync, volume, frequency response, noise figures, channel separation, dynamic range, loudness contour, THD, bass response and timbre are all quite different in the ENCODED 5.1 as opposed to mapped pcm at the bus level. That assumes the editor is not tone-deaf.

Every 5.1 encoder setting (Dialog Norm, Dynamic Range Control, Bitrate, highpass and lowpass filters, phase shift) affect the parameters above. These settings are in addition to the expected compression losses from the encoding itself.

None of these factors can be backported to the timeline because there is no realtime 5.1 encoder at the editing stage (I don't think this has changed). Even at its most transparent settings, the influence of the encoder is still most obvious to the ear and measurement..

That said, for speech (no music), the timeline preview might be just fine.
The HF rolloff and limiting in the encode might actually help it a bit.

But for ANY music or dynamic audio fx, the differences should literally jump out of the speakers if one has even marginal listening skills.

So for any surround project that is to be encoded to 5.1 (excluding mapped PCM), the encode IS the preview.

So you're saying if I take a 5.1 project, render out to DVD mpeg/ac3, encode to DVD, then re-import the DVD to Vegas it won't be the same?

I said that if I preview (or render 6 ch discrete pcm) from the 5.1 project timeline, then render the timeline to ac3 surround, the playback will sound remarkably different over the same audio system.

My goodness. Have you actually tried this?

Whoa.

I've done a dozen or so DolbyDigital2/2 surround-sound documentaries over the years. Never noticed any hint of difference in the final DVD versus what I previewed using Vegas7 back then. None of the various parameters seemed to color the encode in any way. Setting DialogNorm to -31 set the output gain to unity.

Am I missing something in this conversation? Wouldn't be the first time.

Regarding the OP topic, it would seem to me that doing a video render to DVavi and then using just that single video track while working on the audio would dedicate 99.9% of the CPU to just audio. But the issue must be something else--I can't imagine 5.1 bogging down ANY system, let alone a powerful one.