c++mlt

Segmentation fault in default example of mlt++

I am compiling a default example of mlt++ using C++20, specifically the Playlist example (scroll down), but also tried the default Consumer + Producer example.

I compiled the example fine. Running with ./program file1 file2 ... outputs Segmentation fault (core dumped). Running with debugger lldb outputs some more details: issue appears to be in c.connect(p);, but I don't know what to do next.

Basic repro and debugging details:

* thread #1, name = 'SimplePodcastMa', stop reason = signal SIGSEGV: address not mapped to object (fault address: 0x38)
    frame #0: 0x00007ffff7bc0ec0 libmlt-7.so.7`mlt_service_connect_producer + 34
libmlt-7.so.7`mlt_service_connect_producer:
->  0x7ffff7bc0ec0 <+34>: movq   0x38(%rax), %rax
    0x7ffff7bc0ec4 <+38>: movq   %rax, -0x10(%rbp)
    0x7ffff7bc0ec8 <+42>: cmpl   $-0x1, -0x34(%rbp)
    0x7ffff7bc0ecc <+46>: jne    0x7ffff7bc0ed5 ; <+55>
(lldb) up
frame #1: 0x00007ffff7f8fc00 libmlt++-7.so.7`Mlt::Service::connect_producer(Mlt::Service&, int) + 92
libmlt++-7.so.7`Mlt::Service::connect_producer:
->  0x7ffff7f8fc00 <+92>: movq   -0x8(%rbp), %rbx
    0x7ffff7f8fc04 <+96>: leave
    0x7ffff7f8fc05 <+97>: retq

libmlt++-7.so.7`Mlt::Service::insert_producer:
    0x7ffff7f8fc06 <+0>:  endbr64
(lldb) up
frame #2: 0x00007ffff7f85cf6 libmlt++-7.so.7`Mlt::Consumer::connect(Mlt::Service&) + 44
libmlt++-7.so.7`Mlt::Consumer::connect:
->  0x7ffff7f85cf6 <+44>: leave
    0x7ffff7f85cf7 <+45>: retq

libmlt++-7.so.7`Mlt::Consumer::start:
    0x7ffff7f85cf8 <+0>:  endbr64
    0x7ffff7f85cfc <+4>:  pushq  %rbp
(lldb) up
frame #3: 0x0000555555555634 SimplePodcastMaker`main(argc=1, argv=0x00007fffffffdc78) at main.cpp:47:14
   44       Profile profile;
   45       Producer p( profile, "pango:", "Hello World" );
   46       Consumer c( profile, "sdl" );
-> 47       c.connect( p );
   48       c.run( );
   49       return 0;
   50   }

#include <mlt++/Mlt.h>

using namespace std;
using namespace Mlt;

int main(int argc, char **argv)
{
    Factory::init( );
    Profile profile;
    Producer p( profile, "pango:", "Hello World" );
    Consumer c( profile, "sdl" );
    c.connect( p );
    c.run( );
    return 0;
}

Repro at git repo https://gitlab.com/kaixoo/simple-video-podcast-maker, branch cpp-mlp-api

Solution

  • This usually happens because you do not actually have the producer or consumer you have requested. The simple example does not have error checking. For example, in mlt++ you use object.is_valid() to see if underlying C pointer is not null. Run melt -query producers and melt -query consumers to see what you have on your system. Then, adjust the example according to which you have. For example, you might have built with the modern, preferred sdl2 corresponding the SDL version 2 library.