[MPlayer-dev-eng] dwStart (stream delay in AVI files)

[Michael Niedermayer]

Hi

On Wed, Feb 01, 2006 at 01:44:55PM -0800, Corey Hickey wrote:
> Michael Niedermayer wrote:
> > Hi
> > 
> > On Tue, Jan 31, 2006 at 12:51:49AM -0800, Corey Hickey wrote:
> > 
> >>Michael Niedermayer wrote:
> >>
> >>>>>>I _think_ mplayer doesn't properly use the dwStart field in the stream
> >>>>>>header of AVI files. To reproduce, create a file with 10-second audio delay:
> >>>>>>
> >>>>>>mencoder file.avi -ovc copy -oac copy -audio-delay 10 -o delay10.avi
> >>>>>>
> >>>>>>MEncoder writes the audio delay in the dwStart field of the audio
> >>>>>>stream. You can check it with a hex editor or with 'mplayer -v delay10.avi'.
> >>>>>
> >>>>>
> >>>>>MEncoder supports -delay now anyway, you should use that... -audio-delay is 
> >>>>>a hack..
> >>>>
> >>>>Are you sure? That seems to be the intended purpose of dwStart,
> >>>>especially considering that Microsoft's player appears to use it that
> >>>>way and -audio-delay is the documented way to adjust A-V sync with
> >>>>mencoder.
> >>>>
> >>>>Up to this moment I was thinking of using dwStart to compensate for
> >>>>video decoding delay (with B-frames), but then I realized it could be
> >>>>detrimental to remuxing to other containers.
> >>>
> >>>
> >>>which? avi supports dwStart, nut can start at any timestamp too, mpeg-ps/ts
> >>>is fine too, basically a container which requires that the first packet of
> >>>every stream has the absolutly identical pts is quite limited
> >>
> >>Right, but the approach I was considering was to use dwStart to make a
> >>video player play the audio stream with a slight delay, thus matching it
> >>up to the slightly-delayed video frames. Remuxing to a container that
> >>uses pts would result in the video frames being played back without
> >>delay and the dwStart-induced audio delay would be erroneous.
> >>
> >>Here are simplified playback timing tables of what I'm thinking will
> >>happen from using dwStart like that. The numbers
> >>
> >>original   decoding   dwStart-   remuxed
> >>file       delay      adjusted   with PTS
> >>-----------------------------------------
> >>A1  V1     A1                        V1
> >>A2  V2     A2  V1     A1  V1     A1  V2
> >>A3  V3     A3  V2     A2  V2     A2  V3
> >>A4  V4     A4  V3     A3  V3     A3  V4
> >>               V4     A4  V4     A4
> > 
> > 
> > wrong!
> > {A|V}<id><PTS><DTS>
> > original: (lets say its raw)
> > A000 A111 A222 A333
> > V000 V111 V222 V333
> > 
> > decoding delay: (this cannot be stored without either skiping a frame or 
> >                  dwStart in AVI due to the -1 DTS)
> > A000  A111 A222 A333
> > V00-1 V110 V221 V332
> > 
> > decoding delay + skip frame: (stored in AVI)
> > A000 A111 A222 A333
> > V110 V221 V332
> > 
> > ignoring decoding delay: (stored in AVI, 1 frame delay wrong)
> > A000 A111 A222 A333
> > V010 V121 V232 V343
> > 
> > dwStart style:
> > A011 A122 A233 A344
> > V010 V121 V232 V343
> > 
> > all of these remuxed: they stay the same, why in hell should anything change?
> > you find the pts from the dts by using a AVParser and the dts are known from
> > avi
> 
> I guess I was assuming that the remuxing program wouldn't know about the
> decoding delay and would assign video PTS starting at 0 rather than at 1.
> dwStart style, remuxed (incorrect; how I thought it was):
> A011  A122 A233 A344
> V00-1 V110 V221 V332

well that makes absolutely no sense, there can be no -1 dts in AVI its not
possible

[...]
-- 
Michael