ffmpeg: fix small warning on output.
ffmpeg: fix small warning on output.

tschmidt23/Pangolin,stevenlovegrove/Pangolin,randi120/Pangolin,wxdzju/Pangolin,tschmidt23/Pangolin,wxdzju/Pangolin,stevenlovegrove/Pangolin,stevenlovegrove/Pangolin,renzodenardi/Pangolin,randi120/Pangolin,renzodenardi/Pangolin,mp3guy/Pangolin,tschmidt23/Pangolin,mp3guy/Pangolin,mp3guy/Pangolin