1280x720 mpeg-2 to xvid bitrate suggestion

[graysky]

What is a standard bitrate people use when encoding 720p to xvid? I'm assuming a Qf of 0.25 would be good?

bitrate = vertical res x horizontal res x fps x Qf x 1/1000
bitrate = 720x1280x60x0.25
bitrate = ~8,400 kbps ??? <-- seems kinda high

Problem is that 60 fps factor... how are people handling this?

[jagabo]

Single pass constant quantizer. Set the quantizer to whatever quality you want. Try 3 to start (the higher the Q, the lower the quality and the smaller the file). Encode.

[graysky]

I thought 2-pass encoding gave better results? Bitrate is bitrate and is independent of method isn't it? In other words, what does a setting of 3 equate to in terms of kbps?

[jagabo]

Two pass VBR encoding gives better results than single pass CBR encoding. Target (aka constant) Quantizer encoding gives whatever quality you ask for.

With two pass encoding you know how big the file will turn out but you don't really know what the quality will be. All you know is that the quality will be the best the encoder can do with that bitrate.

With Target Quantizer encoding you know what the quality will be but you don't know how big the file will turn out. You select the quality and the encoder uses whatever bitrate is necessary (at each frame) to maintain that quality.

If you create files of the same size using both methods the quality will be about the same.

[manono]

Hi-

bitrate = ~8,400 kbps ??? <-- seems kinda high

Probably, but maybe not. Depends on the compressiblity of the source. And also on whether or not you bring it back down to 23.976fps (or 29.97fps if from a video source) from its capture framerate of 59.94fps.

You might look at it this way. A "normal" widescreen AVI might be:
624x352=219648 pixels
1280x720=921600 pixels
921600/219648=4.1958.

The same show encoded for 1280x720 needs over 4 times the bitrate to encode for the same quality as the same show reduced to 624x352. If a 50 minute show at 624x352 normally is done for 350 MB, then you'll need 1400 MB or more to do it for the same quality at the higher resolution. And that quality might not be very high.

And if size isn't really a concern, and quality is a concern, then following jagabo's suggestion will get you the best results. And if quality is the main concern, size be damned, then a combo of 1-pass encoding for a low Q, combined with the use of a high quality quantisation matrix (Didee's SixOfNine, or Fox Home Entertainment, for example), will leave you astounded at the quality. Be careful, though, as it's easy to fill a full DVDR doing that.

[jman98]

I'm getting really good results by using bit rates of 3000-3500 on 720p encodes of high def TV captures. I use Dr. Divx, do 2 pass encoding, and Dr. Divx automatically converts the fps to 29.97. I'm not seeing any motion problems. I have no interest at all in trying to IVTC to 24 fps, if appropriate. It's a super big deal to some people, but it's just not worth the effort to me. I'm kind of skeptical that converting 60 fps to 24, if applicable, is a very good idea, but if you or others disagree, that's fine.