[FFmpeg-devel] [PATCH] fix H.264 crash (issue 706)

[Reimar Döffinger]

On Thu, Apr 09, 2009 at 07:24:19PM +0200, Michael Niedermayer wrote:
> On Thu, Apr 09, 2009 at 12:17:43PM +0200, Reimar D?ffinger wrote:
> > Hello,
> > it is quite possible this just hides the real issue, but on the other hand it
> > looks like a simple and not too ugly fix to me.
> > Comments?
> 
> the fix is definitly not correct
> a correct fix very likely would be in the error concealment code,
> basically it should throw away motion vectors to non existing frames
> or make sure they exist

Is attached patch what you had in mind? I am not sure if the B-frames
case is so good, I guess it might be a bit asymmetric if only one of
the reference frames is missing.
There is one more case that sets mv_dir, in the lower part of guess_mv,
but since there already is an
> assert(s->last_picture_ptr && s->last_picture_ptr->data[0]);
I assumed that one will not need any changes, I did not actually verify
that though...
-------------- next part --------------
Index: libavcodec/error_resilience.c
===================================================================
--- libavcodec/error_resilience.c	(revision 18389)
+++ libavcodec/error_resilience.c	(working copy)
@@ -343,6 +343,7 @@
 
                 if(IS_INTRA(s->current_picture.mb_type[mb_xy]))  continue;
                 if(!(s->error_status_table[mb_xy]&MV_ERROR)) continue;
+                if(!s->last_picture.data[0]) continue;
 
                 s->mv_dir = MV_DIR_FORWARD;
                 s->mb_intra=0;
@@ -870,6 +871,7 @@
             if(IS_INTRA(mb_type)) continue; //intra
             if(error&MV_ERROR) continue;              //inter with damaged MV
             if(!(error&AC_ERROR)) continue;           //undamaged inter
+            if(!s->last_picture.data[0]) continue;
 
             s->mv_dir = MV_DIR_FORWARD;
             s->mb_intra=0;
@@ -908,8 +910,11 @@
                 if(IS_INTRA(mb_type)) continue;
                 if(!(error&MV_ERROR)) continue;           //inter with undamaged MV
                 if(!(error&AC_ERROR)) continue;           //undamaged inter
+                if(!s->last_picture.data[0] && !s->next_picture.data[0]) continue;
 
                 s->mv_dir = MV_DIR_FORWARD|MV_DIR_BACKWARD;
+                if(!s->last_picture.data[0]) s->mv_dir &= ~MV_DIR_FORWARD;
+                if(!s->next_picture.data[0]) s->mv_dir &= ~MV_DIR_BACKWARD;
                 s->mb_intra=0;
                 s->mv_type = MV_TYPE_16X16;
                 s->mb_skipped=0;