doc/encoders: add libvorbis doc

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
doc/codecs: update skip_alpha documentation

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
lavc/libmp3lame: fix alignment and capitalization in AVOptions

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
lavc/libmp3lame: add comments about CBR/VBR modes

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
lavd/x11grab: Support AV_PIX_FMT_PAL8.

Fixes ticket #3068.