[Kdenlive-devel] Color correction tools: How and where to implement them?

[Dan Dennedy]

On Thu, Jul 29, 2010 at 1:29 PM, jb <jb at kdenlive.org> wrote:
> On Thursday 22 July 2010 19:06:22 Dan Dennedy wrote:
>
>>
>> Yeah, this is bad. First of all, the mlt consumer-frame-show event
>> supplies a frame reference, which gets lost in the Kdenlive
>> rendererPosition signal that its frame-show event handler emits. It
>> appears that kdenlive signal was intended purely for position-oriented
>> thing like updating a timecode label, but now you could say it is
>> being abused. Interestingly, when I trace your logic for updating the
>> vectorscope, that frame position is not used. Instead it is a trigger
>> to get the position of the mlt producer for the active monitor. Using
>> the producer's position is the second bad thing. It is not the same
>> position as that in the monitor (the mlt consumer). The producer may
>> read ahead for some parallelism. While we currently keep this low for
>> better latency handling, it is going to go up a little when additional
>> parallelism is introduced. The third bad thing is that to get a frame
>> object, it asks the producer to seek backwards when it may have
>> already moved ahead! This might not be too bad right now due to some
>> frame caching in MLT, but again, with increased parallelism coming, it
>> may become worse. In summary, the scopes should be using the frame
>> object from the mlt frame-show event and avoid jumping through so many
>> hoops.
>
> Hi all.
>
> I had a look at this stuff and tried to use the frame object from the mlt-
> frame-show event, using exactly the same code that is used to get a QImage
> to display on the QGLWidget.
>
> Added code in the consumer_frame_show event looks like this:
>
>    mlt_image_format format = mlt_image_rgb24a;
>    int width = 0;
>    int height = 0;
>    const uchar* image = frame.get_image(format, width, height);
>    QImage qimage(width, height, QImage::Format_ARGB32);
>    memcpy(qimage.bits(), image, width * height * 4);
>    self->gotFrame(qimage);  // send the image for analysis
>
> It works fine when seeking, but if I try to play the clip, it crashes with the
> backtrace copied at the end of the mail.

I will take a closer look this weekend.

> So I am wondering if it is possible to use the frame from the consumer event
> or if something in MLT's design makes it impossible...

I am thinking of 2 possible things. One is that a reference needs to
be added to prevent a premature free on the mlt_frame object. Another
thing is that this callback is initiated from a separate thread and
sometimes painting from a separate thread does not play well with a
toolkit's main thread.

> Any hints welcome.
>
> jb
>
>
> backtrace:
>
>
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0xabb86b70 (LWP 10659)]
> __memcpy_ssse3 () at ../sysdeps/i386/i686/multiarch/memcpy-ssse3.S:1248
> 1248    ../sysdeps/i386/i686/multiarch/memcpy-ssse3.S: No such file or
> directory.
>        in ../sysdeps/i386/i686/multiarch/memcpy-ssse3.S
> (gdb) thread apply all bt
>
> Thread 19 (Thread 0xabb86b70 (LWP 10659)):
> #0  __memcpy_ssse3 () at ../sysdeps/i386/i686/multiarch/memcpy-ssse3.S:1248
> #1  0xabb85ea8 in ?? ()
> #2  0x00143f56 in mlt_consumer_frame_show (listener=0xacf8afc8,
> owner=0x88c7fe0, this=0x88c8560,
>    args=0xabb85ff4) at mlt_consumer.c:276
> #3  0x0013ce2c in mlt_events_fire (this=0x88c8d78, id=0x609c084 "consumer-
> frame-show") at mlt_events.c:215
> #4  0x06098dfd in consumer_frame_show_cb (sdl=0x88d5258, parent=0x88c8d78,
> frame=0x8babb68)
>    at consumer_sdl_preview.c:118
> #5  0x00143f56 in mlt_consumer_frame_show (listener=0xacf8afc8,
> owner=0x88d5258, this=0x88c8d78,
>    args=0xabb86144) at mlt_consumer.c:276
> #6  0x0013ce2c in mlt_events_fire (this=0x88cace8, id=0x609c084 "consumer-
> frame-show") at mlt_events.c:215
> #7  0x06096715 in consumer_play_video (arg=0x88cace8) at consumer_sdl.c:465
> #8  video_thread (arg=0x88cace8) at consumer_sdl.c:698
> #9  0x0097696e in start_thread (arg=0xabb86b70) at pthread_create.c:300
> #10 0x02181a4e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130
>
>
>
>
>
> ------------------------------------------------------------------------------
> The Palm PDK Hot Apps Program offers developers who use the
> Plug-In Development Kit to bring their C/C++ apps to Palm for a share
> of $1 Million in cash or HP Products. Visit us here for more details:
> http://p.sf.net/sfu/dev2dev-palm
> _______________________________________________
> Kdenlive-devel mailing list
> Kdenlive-devel at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/kdenlive-devel
>



-- 
+-DRD-+