This will be useful in the following commit, after which the muxer
timebase is not always available when encoding.

This merges Libav commit 3e265ca5. It was previously skipped.

There are some changes with how/when the mux_timebase field is set,
because the Libav approach often causes a too imprecise time base
to be set. This is hard, because the muxer's write_header function
can readjust the timebase, at which point we might already have
encoded packets buffered. (It might be better to buffer them after
the encoder, instead of after all the timestamp handling logic
before muxing.)

The two FATE tests change because the output time base is raised
for subtitles. (Needed to avoid certain rounding issues in other
cases.)

Includes a minor merge fix by Mark Thompson, and

    avconv: Move rescale to stream timebase before monotonisation

also by Mark Thompson <sw@jkqxz.net>.
Signed-off-by: wm4 <nfxjfg@googlemail.com>

This will test properly CRLF with make fate, make fate-subtitles and any
make fate-sub-* test. Before this commit, the rawdiff was triggered only
by make fate-subtitles.

Also make sure fate-sub-* only match the tests relying on fmtstdout
command, to at least avoid failing on MingW. See
https://ffmpeg.org/pipermail/ffmpeg-devel/2015-April/172395.html

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Fix handling of timestamps which start  far away from 0
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

The sub-movtextenc ref file changes because the dimensions
(400×60) are stored by the format.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

This change introduces a basic encoder for 3GPP Timed Text subtitles,
also known as TX3G, Quicktime subtitles, or "movtext" in the existing
code.

This initial change doesn't attempt to write styling information,
and just writes the plain text of the subtitles. I intend to add
support for styles eventually, but it's challenging due to a lack
of existing players that support them.

Note that an additional change is required to the mov/mp4 muxer to
write empty subtitle packets to indicate subtitle duration.
Signed-off-by: Philip Langdale <philipl@overt.org>