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

[Michael Niedermayer]

Hi

On Thu, Feb 02, 2006 at 11:38:01AM -0800, Corey Hickey wrote:
> Michael Niedermayer wrote:
> > 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
> 
> I meant for other containers. Remuxing to avi should just copy the
> original dwStart values into the new file, I think.

what pts and dts does a frame you demux from avi have? it cannot have -1
never its impossible, so there is no way that you could end up with a -1
dts when muxing unless you do something very strange

if you are speaking about foobar->avi well you have to do something about
negative timestamps in that case anyway if foobar allows them thats
independant of any delay stuff

[...]
-- 
Michael