MPEG seek crash (was: [Ffmpeg-devel] Re: Compiling FFmpeg using ISO/C89 compiler)

[Steve Lhomme]

Michael Niedermayer wrote:
> Hi
> 
> On Sat, Dec 09, 2006 at 05:47:55PM +0100, Reimar D?ffinger wrote:
>> Hello,
>> On Sat, Dec 09, 2006 at 05:09:50PM +0100, Michael Niedermayer wrote:
>>> On Sat, Dec 09, 2006 at 12:07:34PM +0100, Reimar D?ffinger wrote:
>>>> On Fri, Dec 08, 2006 at 05:28:57PM +0100, Baptiste Coudurier wrote:
>>>>> If my chems1.vob is the same one, and anyway it should not crash indeed.
>>>>> I confirm that ffplay_g crash with current svn.
>>>>>
>>>>> Log attached. Hope this helps.
>>>> Can you test attached patch? I guess it is a bit hackish, but I'd really
>>>> like to know what kind of effect it has *g*
>>>>
>>>> Greetings,
>>>> Reimar D?ffinger
>>>> Index: libavcodec/mpegvideo.c
>>>> ===================================================================
>>>> --- libavcodec/mpegvideo.c	(revision 7261)
>>>> +++ libavcodec/mpegvideo.c	(working copy)
>>>> @@ -3905,6 +3905,8 @@
>>>>          return;
>>>>      }
>>>>  #endif
>>>> +    if (!s->last_picture.data) s->mv_dir &= ~MV_DIR_FORWARD;
>>>> +    if (!s->next_picture.data) s->mv_dir &= ~MV_DIR_BACKWARD;
>>>>  
>>> IMHO if either reference frame of a b frame is unavailable then either
>>> A. drop it (easy and logic, and not terribly noticeable)
>>> B. for every MB
>>>     * if its bidir drop the vector for an unavailable frame
>>>     * if its forward or backward and the reference is unavailable
>>>       flip the motion vector (* -1 * difference in temporal distance)
>>>     * if neither reference is available drop the b frame
>>> C. some more complex temporal iterpolation based on available motion vectors
>>>
>>> and my guess would be that B would look bad for most mpeg2 files as most
>>> mpeg2 encoders are trash and select bad motion vectors ...
>> So just
>> if (s->mv_dir & MV_DIR_FORWARD && !s->last_picture.data) return;
>> if (s->mv_dir & MV_DIR_BACKWARD && !s->next_picture.data) return;
>>
>> Instead of the above?
> 
> iam more thinking of
> if(s->pict_type == B_TYPE){
>     if(!s->last_picture.data || !s->next_picture.data)
>         return -1;
> }
> after decoding the header, assumng we are on the right track at all ...
> 
> 
>> Either way, I do not yet even know if either one helps at all *g*
> 
> neither do i ...

None of these solution work here. The last one crashes less often (after 
more seeking), but I only tried a few times each.

Steve

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