Input #0, matroska,webm, from 'input.mkv':
  Duration: 00:55:43.54, start: 0.000000, bitrate: 4008 kb/s
    Stream #0:0(eng): Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
    Stream #0:1(eng): Audio: ac3, 48000 Hz, 5.1(side), s16, 384 kb/s (default)
File 'output.mp4' already exists. Overwrite ? [y/N] y
track 1: codec frame size is not set
Output #0, mp4, to 'output.mp4':
  Metadata:
    encoder         : Lavf54.2.100
    Stream #0:0(eng): Video: h264 (![0][0][0] / 0x0021), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=2-31, 23.98 fps, 1k tbn, 1k tbc (default)
    Stream #0:1(eng): Audio: ac3 ([165][0][0][0] / 0x00A5), 48000 Hz, 5.1(side), 384 kb/s (default)
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Could not write header for output file #0 (incorrect codec parameters ?)
root@localhost:/media/c562c662-acad-4cd2-9a3a-e5b30fc367e9/downloads#