avformat/vobsub: fix seeking.

(cherry picked from commit f8678dcef3c5b0ea82e898e1f419863409fa135f)
avformat/subtitles: check lower bound for duration overlap seeking.

(cherry picked from commit 1ca4bf930bab681a79fb591330043675c7cfd798)
Store the video bit_rate in the context when muxing mxf.

This will allow using rc_max_rate if no bit_rate is specified (on remuxing).

Reviewed-by: Matthieu Bouron
(cherry picked from commit 52cf08b4c8859f7cac010a7a59f7aa369384ad85)
Use rc_max_rate if no video bit_rate was specified when muxing mxf_d10.

Fixes ticket #2945.

Reviewed-by: Matthieu Bouron
(cherry picked from commit d73565d5ddf41d4b7805327cdb271c59d8c3fc59)
doc/encoders: reformat libmp3lame doc

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
(cherry picked from commit 40b8350b57adaa9aaf6731bac5130d4fec1639c3)

Conflicts:
	doc/encoders.texi
doc/encoders: reformat and add some clarification in libtwolame doc

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
(cherry picked from commit e45e72f5f89ef5a5791562cfcb935028b46ecd0a)

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
doc/encoders: Remove options that were not there when branch was cut from master

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
doc/encoders: improve libvo-aacenc doc

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
(cherry picked from commit 81bbe49a0e588aa899f37a567808ba8926d798d6)

Signed-off-by: Timothy Gu <timothygu99@gmail.com>