[MEncoder-users] Compressibility test

Guillaume POIRIER poirierg at gmail.com
Wed Apr 27 16:21:46 CEST 2005


On 4/27/05, Jean Hoderd <jhoderd at yahoo.com> wrote:
> Hi everybody!
> My question is the following: is a pre-pass with
> vqscale=2 a good indicator of the compressibility
> of a file?
> I have a collection of episodes 13 that I want to
> backup to a DVD+R.  Obviously, I could simply
> calculate 4.38GB / 13, and have each episode
> use the same bitrate.  However, I expect that
> some will require a higher bitrate than others.
> Hence the need for some sort of "compressibility
> measure":  I could just do a pre-pass with
> vqscale=2, and use the resulting file size
> to calculate the proportion of the available
> space which should be given to the episode.

My advice would be to encode 10 equally long (e.g. 0.5% of the movie)
sequences distributed at 10 different moments of your movie, all at
quant 2. You want those sequences to add up to around 5 % of the movie
Then, you smash those together and look at their size, which would be
a good enough indicator of its compressibility.

In short: you don't need a full pre-pass, just snippets, to get an
idea of how much each episode needs.


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