riff: Pass block_align to estimate frame duration

Fix incorrect wSamplesPerBlock(=0) written for ADPCM_IMA_WAV

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
Merge commit '584f88409062f7a134e7391887899e8e723ab6ff'

* commit '584f88409062f7a134e7391887899e8e723ab6ff':
  riff: Pass block_align to estimate frame duration

Merged-by: Michael Niedermayer <michaelni@gmx.at>
ffplay: Use av_gettime_relative()

Whenever av_gettime() is used to measure relative period of time,
av_gettime_relative() is prefered as it guarantee monotonic time
on supported platforms.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
Reviewed-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>