Choppy HD preview, even with decent hardware

[Theo Van laar]

There are several options:

select the region you like to have a perfect preview and

Press Ctrl M

or Shift B

or Ctrl Shift M

or Shift M

Theo

[Bob Peterson]

I am struck by your statement that your “disk” is a particular type. That suggests that the machine has one disk. Vegas works much better if the video is on a large, fast HD which is not shared by the OS or other computer programs. IOW, a separate, well organized drive with lots of free space and a fast speed. That would be a good starting point.

[Maurice Calvert]

Thanks for the quick reply.

I’ve indeed tried rendering to RAM. I set aside 10Gb and it took 3 minutes to fill it with 1 minute of video.

The suprising part was that viewing from the rendered RAM was just as choppy (I was of course careful not to change the preview window size). I conclude that the chopiness is not due to rendering, but what could if be?

I’m sure something’s glaring me in the face, but I can’t see it >;-)

Any ideas?

[Maurice Calvert]

Thanks.

I didn’t want bore with all my hardware. I use an 80Gb SSD (it’s not a disk, it’s memory that behaves like a disk, with a seek time of 0 and a huge data rate), as a work drive dedicated to the source videos. The render output is directed to a separate WD Caviar 15’000 rpm SATA drive. The operating system is yet elsewhere, and with 16Gb, I’ve disabled all paging, no need.

In a nutshell, I’m praying it’s not the disks, as there’s little else I can do to improve things >;-)

[Jeremy Rasnic]

You said above that you set aside 10gigs of ram for previewing. That may very well be your issue. Change your ram settings in Vegas to something like 16megs or 32 megs or 512megs and see if your previewing smoothness increases.

Don’t ask me why this works… but it has been known to address choppy previews.

j razz

https://www.jrazzcreations.com

[Chris Young]

Any of the AVCHD files generated by today’s small HD cameras are virtually unplayable in their native form. They are extremely difficult to decode highly compressed long GOP files and even on powerful PCs will cause stuttering playback and in some cases hang the PC. The sooner we all realise that AVCHD is an acquisition format and NOT an editing format the better off we will all be. We run into AVCHD files every week from onboard racecar cameras on a TV show we do and found the following workflow the best solution in Vegas 9.0.

The first thing we do is drop all the files into Cineform’s NeoScene which quickly batch encodes them all to Cineform HD ‘I’ frame based files that play as smooth as butter in Vegas and use less CPU power than regular DV. Editing them then is a snap. When you have finished your edit then export back to AVCHD if you have to. Though in my wildest dreams I can’t see why one would go back to AVCHD unless you want to put them back onto a memory card in a camera for some reason or other.

Chris Young
CYV Productions
Sydney

[Maurice Calvert]

I don’t know how to thank you enough, I was getting to the end of my tether.

The mistake I made was not thinking about the amount of data. A quick calculation led me to this, which I hope others may find useful:

The video I am working on is 102 minutes, which from the above means that the raw data shot was 338Gbytes if it were truly uncompressed.

I converted my 19Gbytes of source with Neoscene, which produced 123Gbytes of (still quite compressed) data. This confirms Neoscene’s estimate of better than 3-1 compression ratio. On my 8-core machine, it took 75 minutes, with about 6 of the 8 cores busy on average.

Let us assume that 60% of the work was decoding AVCHD, 30% encoding Neoscene (it’s suppposed to be relatively simple) and 10% overhead for I/O.

60% of 75 minutes = 45 minutes to decode 102 minutes = 26 seconds of CPU per minute decoded.
6 cores at 2.5Ghz = 15Ghz. 15Ghz * 26 / 60 = 6.5Ghz to decode in real-time.

Because of its structure, AVCHD cannot be decoded in parallel in real-time (see P.S. below), thus to preview AVCHD in real time, you need a processor with 6.5Ghz cores, which AFAIK is currently impossible due to the laws of physics.

All this goes to confirm what many have discovered the hard way, and despite fanciful advertising by the software makers, it just can’t be done.

P.S. I appear to contradict myself, as Cineform decodes in parallel. It does so by cutting the video into pieces (of X seconds), decoding the pieces in parallel, and re-assembling them afterwards. Obviously, you can’t do this for real-time preview.

Needless to say, I stand to be corrected…

HTH and many thanks again!

[Mike Mint]

“I converted my 19Gbytes of source with Neoscene, which produced 123Gbytes of (still quite compressed) data.”

does that mean the Neoscene uncompresses the data, processes it, then re-compresses it?

[Chris Young]

Basically you are correct. The AVCHD files are decoded and re-encoded to the Cineform codec, which can be best described as an intermediate ‘lossless’ high quality codec. There are preset options in Neoscene where you can choose the HD quality that you want Neoscene to use.

Once Neoscence is installed the Cineform codec is now available under the Vegas Render as, Uncompressed AVI, ‘Custom’ menu button where there are a host of coding options for rendering out if you wish to convert using Vegas. Cineform in Vegas gives us the workflow equivalent of ProRes in FCP and DNxHD in Avid. Short of going totally ‘uncompressed’ Cineform is going to give you about the best picture quality from AVCHD you will ever get.

Certain Cineform software packages can go up to Cineform ‘Raw’ coding as was used on the movie Slumdog Millionaire. To get a better understanding of how Cineform works try listening to:

https://odeo.com/episodes/24170637-Filmmaking-Central-Podcast-Ep-5-2009-Cineform%E2%80%99s-David-Taylor

Chris Young
CYV Productions
Sydney

[Mike Mint]

awesome response!

thank you so much for the podcast! that really helped!