Two pass encode question

Khannie

Ok...let's say I want to xvid a file that I already have in mpeg format and I want good quality for equivalent file size, so I go with a two pass encode.....My question is this:

Does the first pass ignore sound?

I mean....if I'm ditching any possible video output from the first pass (just to get the stats file for pass 2) does re-encoding the sound to the final format affect the output stats file?

For those familiar with mencoder, should I do this:

mencoder file.mpg -ovc xvid -xvidencopts pass=1:bitrate=1000 -ovc mp3lame -lameopts vol=0:mode=0:cbr:br=128 -o /dev/null (NULL on windows)

or this:

mencoder file.mpg -ovc xvid -xvidencopts pass=1:bitrate=1000 -ovc copy -o /dev/null (NULL on windows)

if my 2nd pass will use -ovc mp3lame -lameopts vol=0:mode=0:cbr:br=128 for sound encoding. The 2nd option would save a fair bit of processing.

Is the answer to the above codec specific?

Thanks for reading.

ricey

If i was you id use gordian knot and virtual dub its by far the
best way. here is a easy step by step guide...
http://www.gigasize.com/get.php/66081/DVD.Ripping._.XviD.Encoding.Tutorial.PACK-DEZTiNi.rar

Follow that and you cant go wrong. The guide is for dvd vobs
but works the same for mpeg files.

Khannie

It's more of a general question. (I don't use windows. ) I don't actually have an mpeg that I want to transcode, but I am interested in saving time on 2 pass encodes in general (I encode a lot of stuff for my psp to wile away the hours on the train).

I was only using mencoder as an example, though it is what I use.

ricey

Dont really see how you can save time on encodes its all down to
your pc power.

Khannie

Normally that's true, but not in this case (or that's the question).

The first pass could be sped up substantially by just copying the audio stream (effectively ignoring it) instead of encoding it to mp3 (_IF_ this has no effect on the first pass' stats file), since it would be encoded to mp3 in the second pass and stored there. It's a question of whether or not the audio needs to be encoded twice (the video clearly does need 2 encodes).

Khannie

So I just ran some tests...

Short story: If you're encoding the audio to something other than the source files type, you need to encode it twice with a two pass encode.

Here's what I did:

encode 1st pass with mp3, save log file
encode 1st pass with mp3, compare against previous log file (no difference, so it's consistent at least)
encode 1st pass but copy audio stream instead of encoding it, log files differ.