[MPlayer-G2-dev] Re: Question for Arpi :)

[Andriy N. Gritsenko]

    Hi, Arpi!

Sometime (on Thursday, July 24 at 19:37) I've received something...
[.......]
>Differences in video filters:
>=============================
>By default, everything works the same way as in G1, except that put_image
>won't call next filter's put_image directly, but return the dmpi.
>So, instead of 'return vf_next_put_image(vf,dmpi);' you have to write
>'return dmpi;' now. And, isntead of 'return 0;' you write 'return NULL;'.

>Additionally, filters also have a 'drop' parameter, to allow frame
>dropping at filters. By default you can ignore this flag, your put_image()
>won't be called when drop!=0.

>Let's see the non-default case now:
>Your filters may set 2 special flags to control frame dropping:

>// filter wants process_image() to be called with mpi=NULL for dropped frames
>#define VFCAP_NOTIFY_DROPPED_FRAMES 0x2000

>// filter wants to see all frames, even if we want to drop them...
>// (so you can't drop frame above this filter)
>#define VFCAP_WANTS_DROPPED_FRAMES 0x4000

>As you can see, the 'drop' flag has effect only with VFCAP_WANTS_DROPPED_FRAMES.
>These flags will allow filters to be notified about dropped frames, it's
>required for pattern-matching (like inverse telecine) filters and temporal
>postprocessing filters.

    Hmm, I've analyzed the sources and didn't get it at all. If we call
vf_process_image(vf_last,0) for bottom filter (vo or muxer) then any
filter could not get parameter drop as 1. If we call vf_process_image
with drop=1 (well, we are about to drop this frame) then again, we never
can let filter with VFCAP_WANTS_DROPPED_FRAMES get frame if we dropped it
above, because if some filter above drop frame it will return mpi==NULL.
So I can see how flag VFCAP_NOTIFY_DROPPED_FRAMES works but flag
VFCAP_WANTS_DROPPED_FRAMES will work only if no filter above could drop
frames. But if there is no filter above which could drop frames then that
flag has no sence - filter with VFCAP_WANTS_DROPPED_FRAMES will _always_
get _all_ frames already. :)

    So, example: we have demuxer->filter1->filter2->muxer chain. Filter1
may drop frames, filter2 has both flags VFCAP_WANTS_DROPPED_FRAMES and
VFCAP_NOTIFY_DROPPED_FRAMES. Then we have next choises:

1) muxer wants to drop that frame: drop==1. Filter2 may get the frame or
NULL (if filter1 has VFCAP_NOTIFY_DROPPED_FRAMES too).
2) muxer doesn't force to drop that frame: drop==0. Filter1 wants that
frame be dropped. Filter2 will get NULL as mpi.
3) drop==0, filter1 doesn't drop the frame. Filter2 will get the frame.

    So as you can see, VFCAP_WANTS_DROPPED_FRAMES has no effect at all.
May be you have to modify vf.c:vf_process_image() function and get that
behavior you mentioned above?
    Moreover, no filter with VFCAP_NOTIFY_DROPPED_FRAMES will be notified
about dropped frames when drop==1 and no VFCAP_WANTS_DROPPED_FRAMES for
that filter or below, see your source.

    With best wishes.
    Andriy.