[FFmpeg-devel] [PATCH 2/2] avcodec/h264_slice: Never call get_format() for just checking if the format matches

[wm4]

On Sun, 11 Oct 2015 23:00:07 +0200
Hendrik Leppkes <h.leppkes at gmail.com> wrote:

> On Sun, Oct 11, 2015 at 10:43 PM, wm4 <nfxjfg at googlemail.com> wrote:
> > On Sun, 11 Oct 2015 21:55:12 +0200
> > Michael Niedermayer <michael at niedermayer.cc> wrote:
> >
> >> On Sun, Oct 11, 2015 at 09:39:32PM +0200, wm4 wrote:
> >> > On Sun, 11 Oct 2015 21:16:27 +0200
> >> > Michael Niedermayer <michaelni at gmx.at> wrote:
> >> >
> >> > > From: Michael Niedermayer <michael at niedermayer.cc>
> >> > >
> >> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> >> > > ---
> >> > >  libavcodec/h264_slice.c |    4 ++++
> >> > >  1 file changed, 4 insertions(+)
> >> > >
> >> > > diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
> >> > > index cce97d9..daa3737 100644
> >> > > --- a/libavcodec/h264_slice.c
> >> > > +++ b/libavcodec/h264_slice.c
> >> > > @@ -985,6 +985,10 @@ static enum AVPixelFormat get_pixel_format(H264Context *h, int force_callback)
> >> > >      for (i=0; choices[i] != AV_PIX_FMT_NONE; i++)
> >> > >          if (non_j_pixfmt(choices[i]) == non_j_pixfmt(h->avctx->pix_fmt) && !force_callback)
> >> > >              return choices[i];
> >> > > +
> >> > > +    if (!force_callback)
> >> > > +        return AV_PIX_FMT_NONE;
> >> > > +
> >> > >      return ff_thread_get_format(h->avctx, choices);
> >> > >  }
> >> > >
> >> >
> >> > So if I can see this right, the whole purpose of this is to check
> >> > whether the h264 parameters map to a lavc pixfmt, and bail out or
> >> > reinitialize if it doesn't. Why can't this be delayed later? What
> >> > actually needs it sooner than the first "real" get_format? For dealing
> >>
> >> > with paramater changes, why can't it check the raw parameters instead?
> >>
> >> The raw parameters are checked as well but iam not sure these checks
> >> are complete, they are more complex.
> >>
> >
> > I've checked again. 3 parameters influence the pixfmt:
> > bit_depth_luma, chroma_format_idc, and colorspace. Maybe add
> > color_range because of the J formats.  The first two are already
> > checked (lazily, if the SPS changes). A colorspace change also triggers
> > reinit, although the check for it is buried somewhat deeper in the
> > code. (Also I see a potential bug there: are colorspace and other
> > fields not reset correctly if the SPS changes, and the new SPS doesn't
> > have these fields set anymore?) A changing color_range does not force
> > reinit; this must be fixed (although I'd prefer dropping the J hack
> > completely).
> >
> > So do you agree that checks for colorspace and color_range should be
> > added, and that they should trigger reinit, and that this combined with
> > my patch would fix all the potential issues the patch could introduce?
> 
>  Color Range and Color Space should not trigger a re-init, its
> pointless and may disrupt playback if a HWAccel re-inits.
> The in-memory representaiton, and as such the surface format, do not
> change when only these two change, so re-initing makes no sense to me.
> I have specifically hacked my local fork to avoid this because it can
> disrupt playback.

What kind of stream did you deal with that changed color range/space so
often, and was it one of those single-sample-fixes?