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)
avformat/srtdec: skip initial random line breaks.

I found a bunch of (recent) SRT files in the wild with 3 to 10 line
breaks at the beginning.

(cherry picked from commit cfcd55db164e0acc0c30b2cf084e6eebe9741d34)

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
avformat/subtitles: add a next line jumper and use it.

This fixes a bunch of possible overread in avformat with the idiom p +=
strcspn(p, "\n") + 1 (strcspn() can focus on the trailing '\0' if no
'\n' is found, so the +1 leads to an overread).

Note on lavf/matroskaenc: no extra subtitles.o Makefile dependency is
added because only the header is required for ff_subtitles_next_line().

Note on lavf/mpsubdec: code gets slightly complex to avoid an infinite
loop in the probing since there is no more forced increment.

NOTE:
Code of function ff_subtitles_next_line fixed by Alexander Strasser.

The original code from master did test the wrong character, but was
corrected by a subsequent commit. That commit however is not backported,
so it had to be fixed in this commit for the backport.

Conflicts:
	libavformat/mpl2dec.c

(cherry picked from commit 90fc00a623de44e137fe1601b91356e8cd8bdd54)

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
avcodec/srtdec: fix potential overread.

(cherry picked from commit 3a54c221d574ec944db1eddf9df895808f32bf9e)

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
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/ffmpeg-formats: Add documentation for 3 parameters that have been missing

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit b7dd4598630fb1f890ae060f21a9ec92a103f22d)

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

Conflicts:
	doc/formats.texi