Added --remux-video option

Fixes #6996

- Supported formats declared: mp4, mkv
- Added FFmpegVideoRemuxerPP as postprocessor
- Added option to README and shell-completion scripts

youtube_dl/options.py

@@ -790,6 +790,10 @@ def parseOpts(overrideArguments=None):
         '--audio-quality', metavar='QUALITY',
         dest='audioquality', default='5',
         help='Specify ffmpeg/avconv audio quality, insert a value between 0 (better) and 9 (worse) for VBR or a specific bitrate like 128K (default %default)')
+    postproc.add_option(
+        '--remux-video',
+        metavar='FORMAT', dest='remuxvideo', default=None,
+        help='Remux the video to another container format if necessary (currently supported: mp4|mkv, target container format must support video / audio encoding, remuxing may fail)')
     postproc.add_option(
         '--recode-video',
         metavar='FORMAT', dest='recodevideo', default=None,