[Libav-user] FFmpeg + OpenAL - playback streaming sound from video won't work

Carl Eugen Hoyos cehoyos at ag.or.at
Tue Jan 28 13:22:03 CET 2014

Jan Drabner <jan at ...> writes:

> But I never asked for support. I reported what is in my 
> opinion bug.

Let's see.

> swr_convert crashes under some circumstances, 


> without telling any reason. 

Yes and no.
If you had provided a backtrace as requested on 
http://ffmpeg.org/bugreports.html I suspect one would 
have been able to see what's wrong.
(Everybody was able to guess what's wrong but it is 
often a bad idea to rely on guessing when answering 
questions here.)

The relevant functions take a pointer to input data 
structures and a pointer to output data structures 
as parameters. In your case, you initialised the 
conversion functions saying "I want to convert to 
a planar format", so the actual conversion function 
expected you to pass a pointer to pointers. But 
instead you passed a pointer to allocated memory 
(it may have been different but this is what 
generally happens). Do you really think there is a 
possibility for the conversion function to know 
(in advance) that dereferencing the pointer you 
passed will lead to a segfault? And do you agree 
that it is impossible to "tell a reason" in this 

> If that is not a bug, or a severely lacking feature or 
> documentation, I don't know what is.

It may be missing documentation (it possibly is) but 
then you should not write "crash" but instead send 
a documentation update (now) to ffmpeg-devel.

> I still have no idea why it should not be possible 
> to convert from any format to any other.

That is exactly what it does.

> sws_scale can do that just fine.

But it will of course also (immediately) crash 
if you pass a pointer to RGB24 after initialising 
for GBRP.

Carl Eugen

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