[MPlayer-users] disagreement between mplayer displayed timecode and -ss flag

[Loren Merritt]

On Mon, 30 Aug 2004, Dean S. Messing wrote:

> I'm trying to extract a small swath of frames from the _Titanic_ DVD
> in order to test some video processing algorithms.  I find the
> approximate beginning of where I want to extract by viewig the DVD and
> watching the "V: xxx.x" timecodes go by on the text output of the
> commandline:
>
>      mplayer dvd://1  -nosound  -monitoraspect 16:9
>
> I find that what I want starts at about "V: 265.0"
>
> But when I then do
>
> mplayer dvd://1  -nosound  -ss 265 -frames 200 -monitoraspect 16:9
>
> what gets played is somewhere around 435 seconds.

That's just the way DVD timecodes work: It's not possible to seek
to a specified position (other than chapter breaks) without scanning the
entire stream up to the target position. That would be very slow, so
MPlayer's default is to guess a byte offset based on the DVD's nominal
average bitrate.

Note: Binary search or other iterative methods would work in some cases,
but the timecodes are not guaranteed to be unique or increasing, (or even
to represent much of anything about the video). Even if most DVDs are
sane, there are plenty where times reset to 0 between episodes, or
occasionally even at random points in the middle of a movie.

Maybe there should be a "trust the timestamps" option, but I'm not
volunteering to write it.

--Loren Merritt