[Libav-user] libswscale mystery (assertion desc failed)

Sampsa Riikonen sampsa.riikonen at iki.fi
Sat Jun 25 15:32:22 CEST 2016


I am passing decoded H264 frames to


If I use (A) the ffmpeg api as installed from ubuntu repositories (i.e. 
header files and .so files), everything works ok (it's a version from 

However, if I (B) install and compile ffmpeg myself (from the latest git 
version) and use my program with this version, then I get:

Assertion desc failed at libswscale/swscale_internal.h:679

I added some logging into the function ..

pixdesc.c: const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum 
AVPixelFormat pix_fmt)

.. to see the "pix_fmt" numerical the function is receiving, and got 
some absurd numbers like 0, 3 (i.e. corresponding to uv420p and RGBA, as 
expected), but also quite randomly
other numbers and finally a large 700+ number.  After this the program 

This is a bit obscure, but in any case, any insight is highly appreciated..

Does this look like a memory overflow?
Why is the other library version prone to this error, while the other 
one is not? (the two library versions have different configure parameters)



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