Fix filter graph memory leak#274

Merged

cchampet merged 3 commits intoavTranscoder:developfrom

valnoel:fix_filtergraph_memory_leak

Jul 27, 2016

Commits on Jul 25, 2016

StreamTranscoder: unref the filtergraph output AVFrame after it has been converted
Valentin Noel
committed

Commits on Jul 26, 2016

FilterGraph: adds a warning into the process() method documentation
Valentin Noel
committed
StreamTranscoder: calls the Frame clear() method instead of calling directly the av_frame_unref function
Valentin Noel
committed