aviocat: Check the argv array length before reading element i+1

Signed-off-by: Martin Storsjö <martin@martin.st>
aviocat: Add support for specifying the input duration

This avoids the caller having to calculate the byte rate if wanting
to push a file in a rate resembling realtime.

Signed-off-by: Martin Storsjö <martin@martin.st>
doxy: Add AVFrame to the structured modules
doxy: Document better the available AVFrame flags
mp3enc: add an option for disabling the Xing frame.
mp3enc: allow omitting the id3v2 header with -id3v2_version 0
avconv: print a warning when falling back to default 25fps
yuv4mpeg: set average frame rate
buffersrc: handle non-refcounted frames in av_buffersrc_add_frame() correctly
avisynth: fix setting packet properties

Reviewed-by: Stephen Hutchinson <qyot27@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Anton Khirnov <anton@khirnov.net>