Re: [Mlt-devel] question on usage of MLT Producer

[Dan D. <da...@de...>]

Sorry to take so long,

On Wed, Feb 27, 2008 at 11:15 PM, jaromil <ja...@dy...> wrote:
>  On Wed, Feb 27, 2008 at 11:43:55AM -0800, Dan Dennedy wrote:
>  > On Tue, Feb 26, 2008 at 8:02 AM, jaromil <ja...@dy...> wrote:
>
>  > >  i am  trying to  instantiate a producer  for direct usage  in the
>  > >  simpliest way possible, proceeding as follows:
>  >
>  I need to  have a yuv422 buffer for every  frame, whenever my callback
>  is called in the application. as i mentioned, the threading is handled
>  in freej, it cannot be handled by an mlt_consumer. in case you believe

OK, this should not be a problem.

>  this  is accomplishable by  using an  higher level  of the  API please
>  point me out the way, i'll try that.
>
>  so far my  progresses lead to something that seems  to work better (at
>  least no hard crashes), below a simplified flow:
>
>  init() {
>
>   mlt_factory_init( NULL );
>
>   real_producer = mlt_factory_producer( "fezzik", file );

As we resolved before, "fezzik" could be NULL to use the default,
which is fezzik. If you had used "avformat" you might have noticed
that it works as expected (at least, I think so in most versions, but
not certain), and that might or might not be what you want. The fezzik
producer does two things. First, it is a loader that uses a
fezzik.dict file that contains a mapping of file name extension to a
list of producers to try, and if all fails, then it tries avformat.
Secondly, and this is the important part for you, it automatically
applies a set of filters defined in fezzik.ini. For each line in the
file, it tries each filter in the list until one is successfully
created. The purpose is to "normalise" or "conform" all of the inputs
to some common resolution, color space, aspect ratio, and progressive
scan if needed. You might not want the automatic filters if you just
want to get the pure decoded image.

>
>   mlt_producer_optimise( real_producer );

The mlt_producer_optimise is not necessary for your simple case.

>   service = mlt_producer_service( producer );
>
>  }
>
>
>  feed_every_frame() {
>
>
>   mlt_image_format format = mlt_image_yuv422;
>   mlt_frame frame;
>   uint8_t **image;
>
>   mlt_service_get_frame( service, &frame, 1 );
>
>   mlt_frame_get_image( frame, image, &format, &width, &height, 0 );

There are 2 problems here. First, image should be a single pointer
passed as &image. The function needs to be able to tell you the caller
where the image will be. Here you are passing the pointer by value,
and the address to the image will be lost on return.

Secondly, width and height should be set to what you desire. That is
the purpose of format as well. You express what you desire, but the
producer may not always be able to comply. In the case of fezzik
producer, it applies a filter called "resize." The purpose of this
filter is to pad the image with black in order keeping the original
aspect ratio. This filter currently *requires* that you tell it the
desired width and height. However, it should be able to infer this
from the current profile (defaults to PAL). I am going to commit a
change to fix this now. However, in the meantime, you can either
specify the width and height you want, and fezzik will automatically
add filters that scale and pad, or you should just use the "avformat"
producer.

-- 
+-DRD-+