[Kdenlive-devel] kthumb crash? (was Re: [PATCH mlt] Clear audio and video context to NULL)

[Dan Dennedy]

On Sun, Oct 23, 2011 at 3:38 PM, jb <jb at kdenlive.org> wrote:
> On Friday 14 October 2011 13:31:24 Dan Dennedy wrote:
>
>> I was thinking to do something like that in mlt_multitrack where I am
>> currenty setting that value, but I had not yet decided on whether to
>> add a constant or use double the track count or other.
>>
>> > Mikko, I would be interested to know if these changes have an influence
>> > on the crashes you experienced.
>>
>> I was really curious about that huge stack of invalid clip dialogs.
>> What do you think is going on there?
>
> Using MLT in debug mode, I discovered several cases where FFmpeg did show a
> warning about insufficient thread locking around avcodec open / close.

I have seen these messages before as well, but there are global mutex
locks around all calls to avcodec_open/close.

> After several of this warnings, the avformat producer became corrupted and
> unable to load any clip, or simply crashed, which might be the reason for
> those clips becoming invalid.
>
> These problems were caused by concurrent uses of producers in Kdenlive, and
> also by a "weakness" in the sdl preview consumer that caused such corruption
> when doing the following steps very fast several times:
>
> stop the consumer
> delete the producer
> connect a new producer to the consumer
> start the consumer
>
> Looks like when looping, sometimes the consumer was stopped while starting,

Were you calling consumer.is_stopped() before trying to start it? I do
not criticize you if you were not; it is not exactly obvious you
should need to, but I am wondering if that would help.

> which caused avformat locking issues. I now inserted an event wait to make
> sure the consumer is correctly started before attempting a stop which fixed
> the issue.

Did you learn about an improvement that can be made in mlt in the
process of this?

> I managed to fix almost all cases that showed up on my 4 cores CPU, so
> Kdenlive should hopefully be more stable than ever now.
>
> regards
> jb