I'm programming using mlt framework (#include <mlt/framework/mlt.h>),
and I'm having a segfault after my program runs for long periods (2
times happened after 10 hours run, 1 after 5 hours run). I believe this
might be related to synchronization issues between mlt threads, as I
modify the running playlists and the composite transitions I've planted
on the field while the system is running.
My program setups 5 tracks, track #0 holds a full 768x576 video looping
(10000 times for a 13 secs video), while tracks 1 to 4 holds other
smaller videos that I stop and start all the time. I use composite
transitions so that videos that start or stop do a fade in or fade out
and also set its boundaries.
Something like:
------------------
| ------ ------ |
| | t1 | | t2 | |
| ------ ------ |
| ------ ------ |
| | t3 | | t4 | |
| ------ ------ |
------------------
The program randomly chooses one track from 1 to 4, and switches the
video status of it: if it is running, the video is stopped. If it is
stopped, the video is started. This is done every 1 second, and the
program seems to run fine for the first couple of hours, but never
reached 12 hours of running.
I've managed to start gdb with a core dump, with ubuntu 13.10 version of
mlt (0.8.8-2) with debugging package (libmlt-dbg), and found that the
segfault is in producer_get_frame in mlt_producer.c:616, line is:
if ( self->get_frame == NULL || ( !strcmp( eof, "continue" ) &&
mlt_producer_position( self ) > mlt_producer_get_out( self ) ) )
gdb states self is not NULL, self->get_frame is not NULL, but eof is:
(gdb) info locals
properties = 0x128b3e0
eof = 0x0
speed = 1
clone = 0x128b3e0
result = 1
self = 0x128b3e0
(gdb) print self->get_frame
$10 = (int (*)(mlt_producer, mlt_frame_ptr, int)) 0x7f322005cb80
<producer_get_frame>
Now, on the thread i'm switching the videos on and off, I'm trying to
add a video to the playlist with mlt_playlist_append_io, and the
segfault stopped this thread in the process of setting the property
"eof" to value "continue", so I believe the rendering process is trying
to access eof property which is NULL while another thread is actually
setting this value to "continue".
While messing up with the playlist, I surrounded all the code with:
mlt_service_lock(MLT_PLAYLIST_SERVICE(*_plist));
mlt_service_unlock(MLT_PLAYLIST_SERVICE(*_plist));
hoping that would stop the rendering thread from using the playlist
while I'm modifying it, but maybe I should lock not the playlist but the
tracktor? Any other idea on what could be causing this error? I've
searched the entire mlt-devel mailing list, but couldn't find any
related post.
Can I send the code as an attachment to this list?
Sorry for the long mail :(
Ignacio Jaureguiberry.
--- pieces of the on() / off() video (C++) ------
void on()
{
if (_playing)
return;
// add video to playlist
mlt_producer vid = mlt_factory_producer(profile, NULL, _video);
int original =
mlt_producer_position(mlt_multitrack_producer(multitrack));
mlt_service_lock(MLT_PLAYLIST_SERVICE(*_plist));
mlt_playlist_clear(*_plist);
mlt_playlist_blank(*_plist, original);
mlt_playlist_append_io(*_plist, vid, 0, -1);
// transition for fade video in:
// builds a string like:
"X=32/52:320x180:0;X+25=32/52:320x180:100" for simulating a fade in.
std::string txs = transition_string(original, _x, 0) + ";" +
transition_string(original + 25, _x, 100);
mlt_properties_set(mlt_transition_properties(*_trans), "geometry",
txs.c_str());
mlt_service_unlock(MLT_PLAYLIST_SERVICE(*_plist));
mlt_producer_close(vid);
_playing = true;
}
void off()
{
if (!_playing)
return;
mlt_service_lock(MLT_PLAYLIST_SERVICE(*_plist));
// transition to fade video out:
int original =
mlt_producer_position(mlt_multitrack_producer(multitrack));
// builds a string like:
"X=32/52:320x180:100;X+25=32/52:320x180:0" for simulating a fade out.
std::string txs = transition_string(original - 1, _x, 100) +";"
+transition_string(original + 25, _x, 0);
mlt_properties_set(mlt_transition_properties(*_trans),"geometry",txs.c_str());
mlt_service_unlock(MLT_PLAYLIST_SERVICE(*_plist));
// wait for the fade out the hide the video...
usleep(1000000);
// clear the playlist.
mlt_producer producer = MLT_PLAYLIST_PRODUCER(*_plist);
mlt_service_lock(MLT_PLAYLIST_SERVICE(*_plist));
mlt_playlist_clear(*_plist);
mlt_producer_seek(producer, 0);
mlt_service_unlock(MLT_PLAYLIST_SERVICE(*_plist));
_playing = false;
}
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