HDV Capture - MPEG Video Quality

Kimberly wrote on 8/11/2011, 9:10 PM
For HDV capture, who is leaving the MPEG video quality in the Capture Preferences General Tab at at the default setting of 20? Have you noticed an appreciable change in quality if you increase it to the max of 31?

The Vegas 10 help says you can play around with this setting to see what works best, but I was wondering what people are really doing in their daily processes.

Thanks.

Comments

ushere wrote on 8/11/2011, 10:12 PM
have always left at default - interesting question though.

i suppose if you changed it though you'd be re-encoding?

PeterDuke wrote on 8/12/2011, 12:36 AM
Perhaps a simple capture test of the same material with slider settings of 0, 20 and 31 would show whether it actually did anything.

I always use HDVSplit for HDV, which I presume does a straight digital copy of what is on the tape.
NickHope wrote on 8/12/2011, 3:03 AM
For capture I doubt it affects anything, with the faintly possible exception of incomplete GOPs at the beginning and end of the capture, which would be half a second max.

I also always use HDVSplit.
Chienworks wrote on 8/12/2011, 4:48 AM
Right. If the capture program is doing ANYTHING to the incoming stream except correcting the partial beginning & ending GOPs then that would be a Very Bad Thing.

Seems rather odd that the option even exists.
bigrock wrote on 11/16/2011, 11:50 PM
What exactly is this setting changing? It's default was 25 in 11. That would seem to correspond to the HDV bitrate. Maybe it's the bitrate?
Grazie wrote on 11/17/2011, 12:08 AM
OK, I film in 1440x1080i 35mbs PAL UFF, that is HDV format. Yes? However, all my footage goes directly into MXF files on CF cards. From there it is a straight copy into the Canon Utilty and from there a lightening search using Vegas Media Manager into the Vegas workflow. So no tape, just the HDV format.

I'm assuming that when I've been going out to MPG for DVDs, I'm getting ALL the reso? Yes?

Cheers

- g

PLS wrote on 11/17/2011, 4:01 AM
The HDV standard specifies a compressed bitrate of 25Mbps. The HDV capture referred to here is refering to capture from tape.
PeterWright wrote on 11/17/2011, 5:40 AM
By coincidence I got my Z1 out today for the first time this year, and have been reminding myself how it works - I'm using it this weekend as Fixed Whole Stage Camera for a dance show whilst I do close ups with the EX1. I'm recording via Firewire onto a Sony DR60 HD unit mounted on the camera - and today I did a test shoot for four and a half hours to see that all was well.

After importing the files into Vegas I found that where the DR60 created "continuous" new files there were gaps of between 3 and 12 frames, according to the timecode, from one clip to the next, which I don't remember happening last time I used it .... ages ago.

Interestingly it was always a multiple of 3 frames - either 3, 6 9 or 12. It's not critical, because the chances of not having a usable EX1 shot during those missing frames are slight, and even if it happened there are always workarounds - but I wondered if any other DR60 users had experienced this.

(Incidentally I also came across the receipt for the DR60 (60 Gb), which I bought in 2007 for ... about A$2500. Times have soon changed - recently two 32Gb cards cost A$92 .)
ushere wrote on 11/17/2011, 6:00 AM
peter, how did you bring the files in? (i use a cf on my z5 and use device import or the cf utility which gives me 'clean' joints (there's a pun somewhere there;-)), but i used to get 'dirty' joints (there too) if i simply dragged and dropped.
PeterWright wrote on 11/17/2011, 6:06 AM
Through the Vegas Import / Media function Leslie. I did this directly from the DR60 thru firewire- maybe I should copy to HD first. As I said, it doesn't matter for this job, but could be a problem elsewhere.
johnmeyer wrote on 11/17/2011, 12:19 PM
I just did a little research. This option (the MPEG Video Quality slider) did not exist on Vegas 7 & 8, the first two versions that permitted capturing HDV. I think it first appeared in Vegas 9.

I then found this Sony "white paper:"

SDI to MXF Compressed Capture

Note the name of the paper. You will find in this paper the description of the feature, which also appears in the Vegas help and has already been quoted above. However, in the context of this white paper, it appears pretty clear that this setting was added in order to support analog capture to the MPEG format. If your hardware (computer) isn't fast enough to encode the incoming stream, you can reduce the quality until you quit dropping frames.

For "capture" of HDV (I put that word in quotes because, just like using that word to describe DV tape-to-computer, it is a misnomer), all that happens is a transfer (file copy) of the already-digitized bits, so the quality slider has no effect. One post I read said that you can't even move it from the max setting when capturing HDV, but I didn't test it.

If you want more information, you might search on JohnnyRoy's handle (or on his real name). Apparently he wrote something about this over in the Creative Cow forums, although once I figured out what is going on, I wasn't motivated to actually try to find his posts.