Issue with FFMPEG connection

[jsossa117]

Hello
I was using the rastervis package following chapter 12 tutorial in the book "Displaying Time Series, Spatial, and Space-Time Data with R" but am having problems with the line
movieCMD <- "ffmpeg -r 6 -b 300k -i Rplot%02d.png output.mp4"

After running this line I try

system(movieCMD)

and then I get

system(movieCMD)
ffmpeg version 3.2.4 Copyright (c) 2000-2017 the FFmpeg developers
built with Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.2.4 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --disable-lzma --enable-vda
libavutil 55. 34.101 / 55. 34.101
libavcodec 57. 64.101 / 57. 64.101
libavformat 57. 56.101 / 57. 56.101
libavdevice 57. 1.100 / 57. 1.100
libavfilter 6. 65.100 / 6. 65.100
libavresample 3. 1. 0 / 3. 1. 0
libswscale 4. 2.100 / 4. 2.100
libswresample 2. 3.100 / 2. 3.100
libpostproc 54. 1.100 / 54. 1.100
Option b (video bitrate (please use -b:v)) cannot be applied to input url Rplot%02d.png -- you are trying to apply an input option to an output file or vice versa. Move this option before the file it belongs to.
Error parsing options for input file Rplot%02d.png.
Error opening input files: Invalid argument

I tried changing movieCMD to
movieCMD <- "ffmpeg -r 6 -b:v 300k -i Rplot%02d.png output.mp4"
movieCMD <- "ffmpeg -r 6 -b 300k -i Rplot%02d.png -b:v output.mp4"​

but none of these solved the problem.

Any idea how to solve this?