encoding

[helvete]

Hi

Im using virtualdub. When i try to encode in multipass i get an error message. Tried several codecs, works with single pass, How can this be?

what is the advantage of multipass? less filesize?

[Guest]

What was the exact error message that you received?

[helvete]

For xvid it saids "statsfile not found" then:

Cannot start video compression.
The operation is not supported.
(Error code -1)

For a different codec I use it saids (Error code -100)


About how much does multipass reduce filesize?

[mod]

For xvid it saids "statsfile not found"
In the codec settings for 2nd pass, you have to select the same .pass file generated during the 1st pass.

[Mug Funky]

About how much does multipass reduce filesize?

it's not so much a matter of reducing filesize - 2-pass or multipass allow you to hit an exact filesize or bitrate of your choosing while keeping maximum quality.

the first pass checks the video out to see which parts need more bitrate, etc, and the second pass does the encode. i don't fully understand why 3 or more passes is used in some codecs, but they work like a refinement process.

1-pass VBR can be quite good, but the encoder never knows what's coming up, so it could be wasting too much bitrate on easy scenes, and consequently over-compressing the hard scenes when they come to keep to the target bitrate.

[pelmen]

in multipass encoding the codec needs to save a log file of some sort. often there is a setting in the codec settings where you can turn the log on/off. make sure to look for such a setting and turn it on. on the first pass of a multipass encode you wont get an avi file you can play yet, its only after the second pass that the file can now be played. you can usually keep on running more and more passes to refine the avi even further.

as a result you do usually get a smaller filesize but its not by much. the benefit is the quality of the video itself, each refinement can help the final avi get closer and closer to quality of the original. of course there is always a limit of how good the image will look but i've tested a number codecs extensively with several video quality tools and for 4 passes the improvement amount is around the same each pass.

if you are not impatient its worth doing at least a 2pass encode. even a 2pass "good" divx setting gives a much better avi than a 1pass "insane" setting for the same encoding time. i do all mine in batch lists, doing 3 and 4 pass encoding. also remember that you can save a little time but disabling audio for all passes in the batch and then turn it on for the final pass. audio is currently just single pass, the multipass only applies to video so save the CPU cycles by not touching audio until the last pass.