This works through something called auto-profile. melt opens the producer
once and passes it to mlt_profile_from_producer()
https://www.mltframework.org/doxygen/structmlt__profile__s.html#adf600692f0381afa77a2d23fafbb692d
Then, it re-opens the producer and creates the consumer based on that
profile. Your producer simply needs to report the media width and height
and related properties to facilitate this.
On Wed, Jun 8, 2016 at 1:21 PM Paweł Goliński <golp...@gmail.com> wrote:
> Hello all,
>
> As this is my first mail, I’ll do a short introduction. My name is Pawel
> Golinski and I’m one of the
> students involved in VLMC development as part of GSoC 2016. My current
> objective is to implement
> a libvlc producer and it requires a through understanding of MLT
> internals. The documentation and framework
> are great, but as these are my first steps, I’m having problems with the
> simplest things…
>
> My current problem is that I would like somehow to control consumer’s
> width and height from my producer.
> I’ve noticed that this is somehow being done by the avformat producer,
> which somehow tells sdl consumer
> to resize its window to match the video size. My first guess was, that it
> could be done through width and height
> pointers passed to get_image() function of mlt_frame, but changing these
> don’t cause sdl to resize itself - my
> testing ground is color producer - I’m changing *width and *height to some
> random values at the beginning of
> the function, but this doesn’t cause sdl to resize itself. I’ve also
> searched in some other places, but to no avail.
>
> So, is there a simple explanation of how avformat is doing its magic? To
> be more exact, why calling
> melt avformat:file causes sdl window to be the same size, as the video
> file is pointing to? I suppose it
> cannot be through profile mechanism, as avformat pretty much uses profile
> just to determine fps it has
> to output (right?). Any hints?
>
> Best regards,
> Paweł
>
> ------------------------------------------------------------------------------
>
>
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