[FFmpeg-devel] [RFC] How to fix DR+lavfi+vflip crash

[Michael Niedermayer]

On Sat, Nov 27, 2010 at 04:53:51PM +0100, Stefano Sabatini wrote:
> On date Saturday 2010-11-06 18:21:55 +0100, Stefano Sabatini encoded:
> > On date Saturday 2010-11-06 18:10:04 +0100, Stefano Sabatini encoded:
> > > Hi,
> > > 
> > > as you may know the command:
> > > ffplay INPUT -vf vflip
> > > 
> > > crashes with many video codecs. This is a regression introduced by the
> > > direct rendering feature, since the codec request the frame to use for
> > > putting the decoded frame, it gets a frame with negative linesizes and
> > > crash
> > > 
> > > (BTW the smacker regression also seems to depend on diect
> > > rendering, and precisely with the way the palette is initialized in
> > > avfilter_default_get_buffer, which doesn't use ff_systematic_pal()).
> > > 
> > > A possible first step would be to define a CODEC_CAP_NEG_LINESIZES
> > > capability (suggest a better name), and set it in all the codecs which
> > > currently support this feature (I have no idea which of them, do
> > > you?).
> > > 
> > > At this point I see two solutions. One solution would be to change
> > > get_video_buffer(), and make it invert the buffer when it detects the
> > > negative linesizes && the NEG_LINESIZES capability is not
> > > supported, *or* auto-add another filter just before the ffplay source.
> > > 
> > > Such a filter (vflipfix - suggest better name) would work as a null
> > > filter if the frame is not inverted, and would readjust the frame if
> > > the linesizes are inverted.
> > > 
> > > The second solution seems simpler and cleaner.
> > 
> > To make it even more useful, we may add a capability to the filters,
> > and auto-add the vflip-fix filter when building the filterchain, and
> > fix all the filters which doesn't support negative linesizes.
> 
> Patchset attached.
> -- 
> FFmpeg = Frenzy and Fiendish Magic Plastic Ermetic Game

>  avcodec.h |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 634953e7072d997016e9be769086497234f7ec8c  0001-Add-CODEC_CAP_NEG_LINESIZES.patch
> From da3bf16f9054f619966ddec6fb27a8aa375ad423 Mon Sep 17 00:00:00 2001
> From: Stefano Sabatini <stefano.sabatini-lala at poste.it>
> Date: Sat, 6 Nov 2010 17:05:02 +0100
> Subject: [PATCH] Add CODEC_CAP_NEG_LINESIZES.

lgtm



[...]
>  Makefile      |    1 
>  allfilters.c  |    1 
>  vf_vflipfix.c |  132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 134 insertions(+)
> 7cbd3ac2ed85f675c6a14bdeaec9af60fd0e5d89  0003-Add-vflipfix-filter.patch
> From 4ef5f32725492b2ea4149e6f4aba497fad544739 Mon Sep 17 00:00:00 2001
> From: Stefano Sabatini <stefano.sabatini-lala at poste.it>
> Date: Sat, 6 Nov 2010 20:45:38 +0100
> Subject: [PATCH] Add vflipfix filter.

isnt it easier to handle (lack) of neg linesize support by using the premission
system?
like "i need a readable buffer" vs. "i need a buffer with positive linesize"

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20101203/c6346bf1/attachment.pgp>