[MPlayer-users] Bitrates and File Size

[Joonas Koivunen]

On Monday 25 August 2003 22:37, Ethan John wrote:
> ???
> How were you aware that I did this? In my original email, there was
> nothing to indicate that I did this -- I had a unique subject, deleted
> the quoted text... I'm very confused.
In mails, when replied, an field like this is added: (this is from your mail 
which to I'm currently answering)
In-Reply-To: <200308252233.18693.rzei at mbnet.fi>
Which is used by end-user programs to organize stuff into threads etc. I don't 
know more about this subject though :).

> > AFAIK this is explained in encoding-tips.txt, check it again.
>
> Please, I'm not stupid. I read the doc. It's mentioned briefly at the
> end, but not to my satisifaction. 
Well I meant this part: 

"From time to time there's a question like 'hey,
mencoder creates files that are too small! I specified this bitrate and
the resulting file is 50megs short of the target file size!'. The
reason is probably that the codec already uses the minimum quantizer
for nearly all frames so it simply does not need more bits. A quick
glance at the distribution of the quantizers can be enlightening."

> >> But in practice, this number is too small -- it yields files in the
> >> 600-650 MB range.
> >
> > IMHO  you should target 700MB.
>
> I'm not sure you even read what I was saying -- I didn't mention a
> specific target file size. The formula I think should be correct,
> should be correct for _any_ target file size given a constant bit rate.
If you can't hit the target size, the ratecontrol has decided that this 
quality is enough :) -> "let's not waste anymore bits".

> > Hint: use 3 pass technique. mencoder will tell you a suggested bitrate.
>
> MEncoder's bitrate suggestions are LUDICRIOUSLY small compared to the
> actual bitrates you can get. I used to use these values, but my movies
> came out to be around 500 MB. Those suggested bitrates are bogus.
See above. That quote. If you cannot hit target sizes, your video material is 
too easy for the codec. Those numbers have worked for me almost always, 
though I haven't been encoding for few versions..

> I'll check the file. This may be in the docs, but if it is, it's not
> easy to find and not well explained. Like I said, i've read the docs
> inside and out. The video resolution is usually 640x304 or whatever the
> aspect of the movie is (I calculate it based on the crop information,
> automatically). No matter what, it's weird that a movie will have
> noticeable visual artifacts, still not get up to the bitrate I
> originally suggested, and the file size will be smaller than the
> bitrate.
Could you post your command line? As in all the lavcopts? There might be a bug 
introduced lately, I haven't ever had such expreciences.. (but i've used only 
a bit older versions).

> Besides, my question wasn't about target file size, it was about why
> the bitrate of a movie doesn't accurately determine it's file size.
> Very simple question if you know the answer, I would guess.
I'd guess too. Maybe I haven't got a clue :). Just that I've never had such 
problems.. It seems that Vladimir Mosgalin has got a clean answer for you :) 
Another reply.. Well I keep posting to this thread if I run into same kind of 
problems..

> ethan john
-rzei