lavu/rational: add syntactic sugar.

Add a function to create a rational
and macros for common values.
lavfi/af_amerge: use av_make_q.
lavfi/avf_concat: use av_make_q.
lavfi/vf_tile: use av_make_q.
lavfi/dualinput: fix shortest option.

Fix trac ticket #3315.
avcodec/mjpegdec: Dont skip picture allocation if theres no picture allocated

Fixes Ticket 3245
Merge remote-tracking branch 'cigaes/master'

* cigaes/master:
  lavfi/dualinput: fix shortest option.
  lavfi/vf_tile: use av_make_q.
  lavfi/avf_concat: use av_make_q.
  lavfi/af_amerge: use av_make_q.
  lavu/rational: add syntactic sugar.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avformat/matroskadec: support SVQ3 as generated by mkvtoolnix-6.6.0

Fixes part of Ticket3256

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/matroskadec: support QDM2 as generated by mkvtoolnix-6.7.0

Fixes part of Ticket3256

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ac3: set default matrix encoding modes in parse_frame_header.

Deduplicates some code.
(e)ac3: parse and store the Lt/Rt and LFE mix levels.
(e)ac3: clip surround mix level indexes.

Values 0-2 are reserved, 3 (-1.5dB) should be used instead.
eac3: cosmetics, re-indent.
avformat/matroskadec: identify SMI as SVQ3

Fixes part of Ticket3256

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '1f604f96ea70503caa642f68a85be6074a5b3f46'

* commit '1f604f96ea70503caa642f68a85be6074a5b3f46':
  ac3: set default matrix encoding modes in parse_frame_header.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'c229f571fd3c7d7b567c27c87b2bbcdaee1b0e9f'

* commit 'c229f571fd3c7d7b567c27c87b2bbcdaee1b0e9f':
  (e)ac3: parse and store the Lt/Rt and LFE mix levels.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'ade75fb811500f3e3f284737f123938d83be728f'

* commit 'ade75fb811500f3e3f284737f123938d83be728f':
  (e)ac3: clip surround mix level indexes.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge remote-tracking branch 'qatar/master'

* qatar/master:
  eac3: cosmetics, re-indent.

Merged-by: Michael Niedermayer <michaelni@gmx.at>
lavf: add avformat_get_mov_video_tags() and avformat_get_mov_audio_tags()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vp8: remove redundant "equals 1" test

mb_layout is either zero or non-zero.

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>