Fix nonmonotonic DTS when stitching vfr content

Calculate i_bframe_delay_time from the maximum framerate for the
level instead of the observed framerate when b_stitchable and
b_vfr_input params are enabled. This prevents nonmonotonic DTS
values when stitching high frame rate vfr too low frame rate vfr.
17 jobs for stitchable_vfr in 3 minutes and 26 seconds (queued for 4 seconds)
latest
Name Stage Failure
failed
build-debian-aarch64 Build
+++ pwd
++ LOCAL_INSTALL_DIR=/builds/szatmary/x264/local_install
++ export PKG_CONFIG_LIBDIR=/builds/szatmary/x264/local_install/lib/pkgconfig
++ PKG_CONFIG_LIBDIR=/builds/szatmary/x264/local_install/lib/pkgconfig
++ git clone --depth 1 --branch master https://git.ffmpeg.org/ffmpeg.git ffmpeg
Cloning into 'ffmpeg'...
fatal: unable to access 'https://git.ffmpeg.org/ffmpeg.git/': server certificate verification failed. CAfile: none CRLfile: none
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1

failed
build-debian-amd64 Build
$ set -x # collapsed multi-line command
+++ pwd
++ LOCAL_INSTALL_DIR=/builds/szatmary/x264/local_install
++ export PKG_CONFIG_LIBDIR=/builds/szatmary/x264/local_install/lib/pkgconfig
++ PKG_CONFIG_LIBDIR=/builds/szatmary/x264/local_install/lib/pkgconfig
++ git clone --depth 1 --branch master https://git.ffmpeg.org/ffmpeg.git ffmpeg
Cloning into 'ffmpeg'...
fatal: unable to access 'https://git.ffmpeg.org/ffmpeg.git/': server certificate verification failed. CAfile: none CRLfile: none
Cleaning up file based variables
ERROR: Job failed: exit code 1