[FFmpeg-user] -qcomp 0.8 with no effect

[Hugo Wau]

Hello Carl Eugen,
On 23.09.2012 18:16, Carl Eugen Hoyos wrote:
> Hugo Wau<hugowau<at>  gmx.net>  writes:
>
>    
>>> then you should remove -sameq and add -b:v to set the bitrate.
>>>
>>> from my experience with mencoder, -qcomp is used to balance how bitrate
>>> will be used between high motion and still image, and extremely usefull
>>> with two pass encoding. -qcomp doesn't have effect on resulting size, but
>>> resulting quality.
>>>
>>>        
>> Well, nevertheless it works for me now, I just reduced the size of the
>> video, which with -sameq (CARL, WHAT DOES THIS REALLY MEAN - IF IT IS
>> NOT SAME QUALITY?)
>>      
> Please do not shout;-)
> It means same quantiser (which in your case is
> definitely not same quality).
>
> As correctly explained, -qcomp should be used to affect
> the rate control in two-pass mode. That it also affects
> one-pass encoding is probably not unintended, but i'd
> say you abuse the option (to your disadvantage).
>
> The correct way for you to achieve what you want is to
> calculate a video bit-rate (you know the length of the
> video and the audio size), and use two-pass encoding to
> reach the desired file size.
> (If you are not completely happy with the result, you
> can use -qcomp to change the quality distribution.)
>
> Carl Eugen
>    
Thank you for your explanation. This sounds like an intelligent 
solution. My image size is 720 x 576, the fps rate is 25, so, I should 
have 10,368,000 pixels per second. Yet I don't know the number of bits 
to use for the color.
And even if, what would the ffmpeg command-line look like for this 
two-pass method?
With kind regards,
Hugo