1. Option name should explicitly reflect a dependency on ffmpeg in its name.
2. Description should explicitly emphasize it will only work with ffmpeg downloader.
3. -O should be removed.
4. It should be ignored completely when ffmpeg is not used as external downloader.
So therefore
Various:
. outputformat -> ffmpeg_format (and --ffmpeg-format cmdline)
YoutubeDL.py:
. xxx: prepare_filename() is run before we know the downloader. How do we address this?
downloader/external.py:
. Use temp. var force_mpegts to avoid code duplication
. Don't add -bsf:a if force_mpegts is True (oops! error from last rev)
. re-indent complex if
Allow specifying an output format when using an external downloader,
either through --output-format or -O, in preference to the extractor's
default. This is particularly helpful as -O mkv, to allow Matroska
output from ffmpeg in cases where .mp4 isn't a great answer, such as
while trying to play during the download.