swfdec: do better validation of tag length

Avoids trying to read a packet with 0 or negative size.
Avoids a potential infinite loop due to seeking backwards.

Partially based on a patch by Michael Niedermayer.
swfdec: cosmetics: fix indentation
mxfdec: drop unneeded extradata padding

Found-by: Tomas Härdin <tomas.hardin@codemill.se>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavfi/fps: add shorthand.
doc/filters: extend fps documentation.
lavfi/fps: remove parse opt error message.

See cc650cf0 for more info.
lavr: clarify documentation for avresample_get/set_matrix()
lavr: temporarily store custom matrix in AVAudioResampleContext

This allows AudioMix to be treated the same way as other conversion contexts
and removes the requirement to allocate it at the same time as the
AVAudioResampleContext.

The current matrix get/set functions are split between the public interface
and AudioMix private functions.
doc/filters: fix grammar mistake in setfield documentation

Spotted-by: Tim Nicholson <nichot20@yahoo.com>
lavc/utils: Do not require dimensions for PNG.

pngenc doesnt need them and mplayer doesnt set them.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: Add API to make resample engine selectable.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: make realloc_audio() available outside swresample.c

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: move flush into Resampler

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: add a lowpass default so that each Resampler can have its own default.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
swr: Add SOX resampler support

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/ffmpeg: fix/extend documentation for -copyts
Changelog: update for soxr

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
bfi: fix division by 0

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
cafdec: Check duration before use.

Fix division by 0

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ac3dec: fix out of array read

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>