Does save trimmed clip (DV/AVI) reduce the video quality?

[backert1]

In a previous thread Ken indicated that I could split a DV AVI file in the VS11+ editor and save sections of it to new avi files. After seeing many posts cautioning about redering reducing video quality, I'm a bit confused. When you use multi rim or any other tool in teh editor to create clips and then chose to save the individual clips, a message box appears with a "rendering" progress bar during the save.

Is the "save trimmed clip" operation just saving a portion of the original avi clip with unchanged video quality or is it actually rendering (processing) the video and producing a negative impact on the video quality of the new trimmed avi file?

What I really want is a collection of avi clips rather than the library clips - all for the reason of simplying the assembly of a larger project at a later date. Also it seems like creating DVD at a later date would take less rendering time using the trimmed AVI files, rather than having to extract the library clips from the full length avi's.EOEO

[Black Lab]

If you use Save Trimmed Video it will actually make a new copy of your trimmed video. Look in your working folder. Your original clip will be named something like uvs020508.avi. The new clip will be uvs020508-1.avi.

As long as you are trimming avi clips you will not lose any quality.

[Ken Berry]

DV/AVI is largely regarded as a lossless format. As Black Lab has just said, you can re-render it quite a few times before you would notice any minor degradation in quality. Moreover, SmartRender (which you can use when doing re-renders of DV > DV or mpeg-2 > mpeg-2) means that only the video in the immediate area of an edit will in fact be rendered. So if you cut a long DV clip then 'saved trimmed video', only the area of the cut would be rendered and the rest, not. That is why the 'save trimmed video' process is normally quite fast.

To correct one misconception you appear to have, a final video DVD requires a video to be in mpeg-2 format. So at some stage, your DV (trimmed or untrimmed) is going to have to be converted to DVD-compliant mpeg-2. We recommend you do that as a separate step *after* you have finished all your editing. If you don't do that and insert DV (or your project file) into the burning module, then the conversion will still take place during the burning process. But processing errors can creep in this way, and in fact you don't save any time at all. The DV > mpeg-2 conversion will still take the same amount of time whether done separately or in the burning process.

Too many mpeg-2 > mpeg-2 re-renders, unlike DV, *can* result in noticeable loss of quality. But if the original mpeg-2 is high quality, then you can probably re-encode it 2 or 3 times without seeing any drop in quality (though in fact there will be some minute losses since that is the nature of the algorithms used in mpeg-2 compression -- data is lost each time... )

[backert1]

Hello Ken,

Thanks for the confirmation that AVI file editing and resaving in AVI format is not a quality issue. Just was wondering as VS displays the same "rendering" message bar as during an actual conversion. No misconception - I do understand that standard DVDs need to have Mpeg2 format applied to the avi file at some point. I understand that you are recommending that the conversion be done as a separate step using Share/create video file/dvd/mpeg2 790x480 to make the conversion. Then step 2 using the burn module to produce the DVD. Seems like I need some more drive storage space to the tune of ~4G/ hour of video to hold the mpeg2s prior to burning. Good thing I work for Seagate. I just ordered a 1T firewire drive to handle all this video work. Keep on driving the need for data storage!

Thanks,

Todd

[Black Lab]

You got it, as long as the 790x480 is a typo. Did you mean 720x480?

[Trevor Andrew]

Hi Todd

Dv-Avi files are about 13 Gb per hour.

Dv- Avi-----when you Save Trimmed Clip, you are using 13 Gb per hour.

As recommended the final project should be rendered to DVD-Ntsc/Pal (Mpeg2)
The size of this file is dependent on the length of the video and the bit rate used.

As a guide a bit rate of 8000 kbps will produce a file of 4.3 Gb over one hour.
6000 kbps will allow 90 minutes of video
4000 kbps will allow 120 minutes of video

These should produce a file no larger than 4.3 Gb
This is the capacity of a single layer DVD-R disc. Your video will fit the disc.