Using the same 1st pass for successive 2nd passes

[Wam7]

I am encoding for a smartphone and need to test out various bit-rates. Is it OK to save the 1st pass and then have successive 2nd passes with the ONLY difference being the bit-rate. Rather than doing a 1st pass on each bit-rate I am trying.

[Kopernikus]

Yes, that works

[foxyshadis]

You can actually change a lot of different options without needing a rerun first pass. Something to keep in mind when encoding to low bitrate is to do the first pass at a higher quant. It should match your average fairly closely - a q2 first pass with a ~q16 second pass is going to have quality problems from rate-control errors.

Because of the way xvid's config was designed, the only way to do this in vfw is in quantizer restrictions; remember to loosen them again for the second pass.

[Wam7]

You can actually change a lot of different options without needing a rerun first pass. Something to keep in mind when encoding to low bitrate is to do the first pass at a higher quant. It should match your average fairly closely - a q2 first pass with a ~q16 second pass is going to have quality problems from rate-control errors.

Thanks for the tip. The bit rates I use depending on source are from 175kbps up to 350kbps. In the screen shot below would I be better off changing rate control from 'Weight' to 'Quantizer' say, '3' for first pass and '5' for second? Is this what you mean?

http://www.wam77.pwp.blueyonder.co.uk/Quant.PNG

[foxyshadis]

If your second pass average (for P frames) is around q5, change it to that, if it's more like q3, use that. You can find out by checking out the blue bars on the encoding status window at the end of an encode. q5 should be sufficient for a wide range of low-bitrate encoding though. But switch it back to weight=1.0 for the second pass, or it'll skip the whole point of the second pass. ;)