Leif Andersen Leif Andersen - 1 year ago 76
C Question

Inconsistant rendering in mlt XML and C interface and 'hold' producer and avformat consumer

I am trying to create a short video that is just a single image. (I know its a bit silly, but its a test for something bigger).

The code I have for rendering it is:

#include <framework/mlt.h>
#include <stdlib.h>
#include <unistd.h>

int main() {
if(mlt_factory_init(NULL)) {
mlt_profile p = mlt_profile_init(NULL);
mlt_consumer target = mlt_factory_consumer(p, "avformat",
mlt_producer source = mlt_factory_producer(p, "hold", "/Users/leif/logo.png");
mlt_producer_set_in_and_out(source, 0, 10);
mlt_consumer_connect(target, mlt_producer_service(source));


} else {

return 0;

is this file.

When I run this code and play
, the picture comes out all garbelled. There is a green line in the middle and the logo is superimposed on itself a lot.

On the other hand, if I change the consumer to be SDL, the image plays just fine.

And finally, if I change the consumer to be XML, and then use the melt command line application to render it:

melt -consumer avformat:xmlout.mp4 output.xml

and play the video, it also plays fine.

Is there something I am missing in the avformat consumer that I should be setting? Or something else that I am missing here?

Edit: For reference, the outputted xml file:

<?xml version="1.0" encoding="utf-8"?>
<mlt LC_NUMERIC="en_US.UTF-8" version="6.2.0" root="/Users/leif/src/video/private" title="Anonymous Submission" parent="producer0" in="0" out="10">
<profile description="DV/DVD PAL" width="720" height="576" progressive="0" sample_aspect_num="16" sample_aspect_den="15" display_aspect_num="4" display_aspect_den="3" frame_rate_num="25" frame_rate_den="1" colorspace="601"/>
<producer id="producer0" title="Anonymous Submission" in="0" out="10">
<property name="length">15000</property>
<property name="eof">pause</property>
<property name="resource">/Users/leif/logo.png</property>
<property name="aspect_ratio">1.06667</property>
<property name="frame">0</property>
<property name="method">onefield</property>
<property name="mlt_service">hold</property>
<property name="global_feed">1</property>

Answer Source

From the related bug report:

mlt_factory_profile() is actually a little tricky and unclear because the framework itself does not mandate agreements between producers and consumers. There is a MLT super-producer called "loader" that adds a bunch of normalization filters to facilitate agreement. And when you specify the service parameter to mlt_factory_producer() you are bypassing this producer. You see in the above linked code a reference to MLT_PRODUCER, which has a default of "loader" defined earlier in that file.

So, really, to make things work you should say mlt_factory_producer(p, NULL, "hold:/Users/leif/logo.png");

As for XML, see how producer_xml.c is doing exactly that.

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