ffmpeg: sub2video: set resample size.

Necessary after 04a530f.
fate: merge mapchan and options into ffmpeg.

They were two very short files that cover ffmpeg-specific features.
lavf: move force_codec_ids() up

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavf: Fix codec id forcing with probed codecs

Fixes Ticket2088

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
h264: check SPS entries directly to detect pixel format changes

Comparing AVCodecContext.pix_fmt against the get_pixel_format() return
value has the side effect of calling the get_format() callback on each
slice. Users of the callback will probably handle hardware accelerator
initialization in the callback.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
rawdec: fix NV12

Fixes Ticket646

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavf/vobsub: do not count trailing NUL char in extradata.

See 36e61e24.
lavf: remove generic index flag from text subtitles.

This flag is not necessary.
doc/muxers: fix typos in the segment chapter
doc/muxers: add a dedicated section for segment examples
doc/muxers: adopt new -codec:SPEC syntax in segment example
lavfi/avfiltergraph: check pick_format return code.
examples/muxing: improve error messages.

Illustrate the use of return values, av_err2str and
avcodec_get_name.
fate: add sub2video test.
fate: add missing bitexact flag to scale filter

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
fate/sub2video: move sws flags globally in the filtergraph.

The flags are necessary for the auto inserted scaler (because the
overlay filter needs an alpha channel for the overlay surface).
lavf: move stream==-1 handling from ff_subtitles_queue_seek() to avformat_seek_file()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavu/eval: handle div by zero in mod().

Similarly to 03f5043f5, we use the FTRAPV config setting.
lavu/base64: extend/clarify doxy for the base64 API

Also improve overall consistency.
doc/faq: add -start_number example

Also add example showing cat piping images to ffmpeg.

Signed-off-by: Stefano Sabatini <stefasab@gmail.com>