Rendering DV

yirm wrote on 6/17/2001, 12:36 AM

FIrst of all, I just spent some time reviewing this forum board. Lots of great info - thanks.

My question is if you have captured DV via 1394, and you maybe split it into various events and move things around, or make some cuts, what happens when you render to DV format? Is it recompressed? That is, is it lossy compression over lossy compression?

TIA.

-Jeremy

Comments

SonyEPM wrote on 6/18/2001, 8:57 AM

If it is straight cuts, no other changes to the frames (filters etc), and you save back to avi DV, no recompression will occur.

yirm wrote on 6/18/2001, 9:06 AM

Thanks.

If that's the case then

1) If you open a DV file and render it back to DV (having done nothing to it), it should be the same file size?

2) This would be a good way to conserve disk space on projects. You can first do all your straight cuts, render to DV format, then open your chopped files and add text etc. to them as you want.

One other question (out of curiosity). If you make changes to the audio and then render to DV, does the video portion get recompressed?

Thanks for your help.

-Jeremy

yirm wrote on 6/18/2001, 9:08 AM

Oh, and one more question. If there are changes to portions of the video, are only those portions recompressed or the whole thing?

-Jeremy

SonyEPM wrote on 6/18/2001, 10:33 AM

any change within an event forces recompress for the entire event.

SonyEPM wrote on 6/18/2001, 10:34 AM

audio changes do not force recompress of video.

yirm wrote on 6/18/2001, 6:27 PM

Okay. I just brought over a 356,254 KB clip from my camcorder via 1394 and the SF capture utility 2.0e. I brought it into VideoFactory, and saved as AVI/NTSC DV. The file size of the saved file is 376,951, slightly larger than previously. What is the extra 20 MB?

-Jeremy

SonyEPM wrote on 6/19/2001, 9:32 AM

most of this additional size is due to the audio resampling that is done (in VideoFactory) to compensate for audio sync-drift (as found in DV data from Canon and some Panasonic DV cameras or if you shoot 32k audio). There is zero degradation of the video or audio quality...and the audio will play in sync no matter how long the DV clip. A small amount of header and metadata info is also added to the avi file structure itself during render.

yirm wrote on 6/19/2001, 2:25 PM

Thank you for your replies. I feel better with this understanding.

-Jeremy

FrankM wrote on 6/23/2001, 7:48 PM

Thanks to the previous reply, I finally know why VF does not suffer audio/video sync problems! I initially switched to VF from BlanketyBlank-Wave because of the sync unsolvable sync problems in their DV.