Transcoding: empty encoder buffer at the end of the process
OutputFile: add getter for format context
Transcoder: compute progress duration from output format context
Transcoder: use av_q2d to compute progress duration
clean into AvInputVideo: remove selected stream attribute and set packet size directly from frame size
Merge pull request #132 from valnoel/fix_frame_skipped_at_transcode

Transcoding: empty encoder buffer at the end of the process
Transcoder: switch progress duration computing members (for using automatic cast to double)
Merge pull request #133 from valnoel/fix_progress_bar_length

Fix progress bar length