Re: buffer underflow, any fix?

Le 24 avr. 06 à 17:50, ffmpeg-user-request@xxxxxxxxxxxx a écrit :

> ------------------------------
>
> Message: 6
> Date: Mon, 24 Apr 2006 11:43:09 -0400
> From: T <mlist4suntong@xxxxxxxxx>
> Subject: [Ffmpeg-user] Re: buffer underflow, any fix?
> To: ffmpeg-user@xxxxxxxxxxxx
> Message-ID: <pan.2006.04.24.15.43.08.448760@xxxxxxxxx>
> Content-Type: text/plain; charset=ISO-8859-1
>
> On Sat, 22 Apr 2006 23:05:59 -0400, T wrote:
>
> > What's the reason and is there any fix for the buffer underflow  
> > problem?
> >
> > Ie. when converting video, I get a lot of such errors:
> >
> >   [mpeg @ 0xb7fc9860]buffer underflow
>
> I notice the converted video paused here and there when played back  
> with
> VLC. The sound still continuing, but the picture freezes, sometimes  
> 2 or 3
> seconds, sometimes even nearly 10 seconds. It happened 3 or 4 times  
> in the
> 3-minute clip that I tested.
>
> Is the pausing related with the buffer underflow, or it is a separate
> issue entirely.
>
> > I'm already using VBR, like the following, why I still get buffer
> > underflow?
> >
> > ffmpeg -i "VTS_06_1.VOB" -acodec ac3 -ab 224 -ar 48000 -ac 2 -vcodec
> > mpeg2video -b 3600 -maxrate 4500 -bufsize 224 -sameq -ss 0:6:50 - 
> > vframes
> > 3000 "VTS_06_1.mpg"
>
> thanks a lot.
>
> tong

a buffer underflow (I'm not sure, it just my observation) occurs when  
there is too much information for a specified bitrate

if I specified an encoding in MPEG2 (-bitrate 9000) and the source  
has too much details (like contrasts, lines or ... artefacts),
the number of informations from the source cannot be written in the  
specified bitrate (=range) then the bitrate goes "out of  
range" (higher) and there is a buffer underflow.

Then the buffer underflow is just a non-respect of the specified  
bitrate.

But if the buffer underflow (=non respect of the bitrate) give a too  
high bitrate (theorically 9,8Mbits/s  for audio+video bitrate for  
DVD, in fact 13-15MBits/s with tolerance of DVDPlayer), the buffer in  
the dvd player cannot read your dvd as a stream, and there is a  
freeze (just for info, I read once in an MPEG2, that have a buffer  
underflow during encoding, that its bitrate was more than 60Mbits/s   
during one GOP ;-)).

Hope that someone could explain it with a more technical explanation  
(or with more accuracy, or just not wrong if I mislead)

Then buffer underflow is a real pb for me too, the "-trell" option  
corrected half (and more!) of the buffer underflow, but this option  
seems to be depreciated.
Parameter "-target dvd" doesn't avoid buffer underflow too, I have no  
idea to avoid them (I'm not programmer), may be with a two pass  
encoding?

bye

herve