[FFmpeg-devel] [PATCH] ffplay: fix a crash caused by aborting the video queue

Marton Balint cus at passwd.hu
Sat Aug 27 18:40:27 CEST 2011

On Sat, 27 Aug 2011, avcoder wrote:

> On Sat, Aug 27, 2011 at 6:09 PM, Marton Balint <cus at passwd.hu> wrote:
>> Yes, the patch description is probably not entirely correct, sorry, my
>> mistake. The thought of changing w_index somehow remained in my mind from
>> the time I debugged this.
>> The main problem with the code is that multiple ALLOC events may occur at
>> the same time if we don't pop them from the event queue on abort. If these
>> alloc events tries to allocate the same vp, vp->bmp changes (free-d, and the
>> then allocated again), I typically got the crash when
>> SDL_LockYUVOverlay(vp->bmp) was called from the video thread, after
>> SDL_FreeYUVOverlay(vp->bmp) was called from the main thread.
> Why do you get multiple ALLOC envents?
> I checked the ALLOC events, FF_ALLOC_EVENT is only pushed in
> "queue_picture()" which is called by "video_thread()", it is
> impossible to have MULTIPLE FF_ALLOC_EVENT.

When you abort the video queue, an ALLOC event may be in the event queue. 
When another video_thread() is stared (e.g. when changing the video 
stream) the event from the first video_thread may still be in the queue.


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