[MPlayer-users] accurate VBR info, and more ... with midentify ?

[Nico Sabbi]

Il Thursday 03 April 2008 23:41:25 Juri Mianovich ha scritto:
> 
> Hello,
> 
> 
> --- Nico Sabbi <Nicola.Sabbi at poste.it> wrote:
> 
> > > When I run 'midentify' against a VBR clip (mpeg,
> > or
> > > h.264) I often see either an incorrect number, or
> > a
> > > "0" in the video bitrate.
> > > 
> > > Why is this ?
> > > 
> > > I would like to know three things about a
> > particular
> > > VBR video file:
> > > 
> > > - average bitrate
> > > - peak bitrate
> > > - low/minimum bitrate
> > > 
> > > I realize that midentify does not show me the
> > average
> > > (not sure what it is showing me, when it shows
> > > something >0) and I know that I will need to,
> > > essentially, play the entire clip through in order
> > to
> > > get the peak/minimum bitrates (and probably to get
> > the
> > > average as well).
> > > 
> > > Is there a command line that will tell my system
> > to
> > > play the clip as fast as the CPU will allow it,
> > > without any actual video playback (like midentify)
> > so
> > > that I can get those three numbers as fast as
> > possible
> > > ?
> > > 
> > > Also, out of curiousity, when midentify shows me a
> > VBR
> > > birate of >0, what is it showing me, exactly ?
> > > 
> > > Finally, a lot of clips are giving me either
> > > drastically wrong, or "0.00" for the:
> > > 
> > > ID_LENGTH
> > > 
> > > field in midentify ... is there any mplayer
> > command
> > > line that will show me an accurate length reading
> > for
> > > _all_ video clips?
> > > 
> > > thanks.
> > > 
> > 
> > mencoder -ovc copy -oac copy -o /dev/null file.mpg
> 
> 
> Thank you.  When I run this, I get this at the
> beginning:
> 
> VIDEO:  MPEG2  1280x720  (aspect 3)  59.940 fps 
> 19000.0 kbps (2375.0 kbyte/s)
> 
> So the 19000.0 kbps is just the wrong number I get out
> of midentify ... but I wonder, where does that 19000.0
> kbps come from ?

from meaningless headers in the video bitstream

> 
> When your command finishes, I get:
> 
> Video stream: 17164.721 kbit/s  (2145590 B/s)  size:
> 5733057996 bytes  2672.019 secs  160135 frames
> 
> So is the 17164.721 number the average bitrate ?

yes

> 
> If so, how can I get the peak and minimum bitrate
> numbers ?

eh, unfortunately there's no way to get them with mencoder
or mplayer

> 
> Finally, why does midentify show:
> 
> ID_LENGTH=2573.38

extrapolated => totally invented

> 
> but your command shows:
> 
> 2672.019 secs
> 
> Why two different lengths ?
> 
> Thanks.
> 

the latter one is real