Bitrate Question (WMV to DVD Conversion)

[acid_burn]

Hello,

I'm a huge video newbie, but I'm a software developer (Java, C# mostly) so I'm pretty competent in general.

My question is about converting some WMV files to DVD.

The source files are as follows:

Format: WMV
Audio: 910kbps
Audio Sample Size: 16bit
Channels: 2
Audio Sample Rate: 48hz

Video Data Rate: 772kbps
Video Sample Size: 24 bit

I'm converting them using Nero Vision 2, which I've done successfully for about 10 of these files using Neros highest video quality setting, which is:

NTSC
Bit Rate: 8000kbps
Resolution: 720x480 (CCIR-601 D1)
2-Pass VBR

Audio: LPCM


This is the highest quality settings. My better judgement tells me I'm wasting space and time because the destination settings are of a higher quality than the source file.

My question is about the actual conversion process, though. Since I'm transcoding these files, do I need to transcode into the highest settings as I've done for the first 10 videos?

My thinking is that, say, I chose 7200 kbit/s (just for easy math). That's a 10% reduction from the max of 8000 kbit/s. So will the video I produce at 7200 kbit/s be 10% lower quality than the 8000kbit/s version, or will they be of identical quality since both settings are better than the source video, which is, just to remind you, 772kbps.

In addition to this "percentage of quality" question in my mind, I'm also wondering if all bit rates are created equal. In my mind, perhaps 772kps for WMV is equal to a higher bit rate in DVD/AVI.

So.... in summary, is there reason to convert to a higher bitrate than my source files in this situation? Or, for these purposes, is coverting to 1000 kbit/s the same as 8000 kbit/s since my source file is 772kbps?

Sorry for being such a dufus about this.

[jagabo]

MPEG 2 isn't as efficient as WMV (or Divx/Xvid etc.). You'll need 2 to 4 times as much bitrate when you convert to MPEG 2. You're probably also enlarging the frame size so that will need more bitrate too. 772 kbps WMV to 8000 kbps MPEG2 is probably overkill.

[KBeee]

As jagabo said, 2-4 X the original bitrate seems to keep comparable quality when converting from WMV/AVI to MPEG2. If your WMV files are short enough to go from 1000kbps to 8000kbps VBR, and still fit onto a DVD, then you could try encoding at 4000kbps VBR, and fitting 2 onto your DVD, and veiwing on your TV to see if you can actually see any difference in the quality. You could save some disk space by encoding the audio to AC3 instead of LPCM too, to leave more space for video.

[jagabo]

Nero doesn't support it but many MPEG encoders have a constant quality mode. You pick the quality you want and encode in a single pass. The video comes out with whatever bitrate is necessary to achieve the requested quality at each frame. I usually use this mode when converting 22.5 or 45 minute TV series to DVD. After encoding I put as many episodes as will fit on each DVD.

CCE and TMPGEnc Plus support constant quality encoding.

[acid_burn]

You guys have been a ton of help. These are, as someone mentioned ~22 minute TV shows and, in some cases, segments of TV shows.

On my PC (2ghz, 2gb ram) it takes nearly 3 hours to transcode. With that sort of lead time, it makes trial and error very difficult and frustrating.

The first disk, which, as I said, I defaulted to highest quality, is 8000kbps. The one I'm converting right now, per your suggestions, is 5x the source bitrate, (772 x 5 = 3860) and since the source is 640x480 and the destination is 720x480, I'm taking the 3860x1.5 = 5790.

Long story short, I'm trying this one at 6000kbps.

Also, per your suggestions, I switched to AC3 audio. I was amazed at how much more room I had from this switch alone.

All in all, it looks like I'll be able to fit almost 1.5x as much video on this second disk as I was able to fit on the first disk burned at the HQ. This is the difference between 6 DVDs and 10.

Thanks a million!!