saveVideo: Convert a sequence of images to a video by FFmpeg

Description

This function opens a graphics device to record the images produced in the code expr, then uses FFmpeg to convert these images to a video.

Usage

saveVideo(expr, video.name = "animation.mp4", img.name = "Rplot",  ffmpeg = ani.options("ffmpeg"), other.opts = if (grepl("[.]mp4$",  video.name)) "-pix_fmt yuv420p", ...)

Arguments

expr

the R code to draw (several) plots

video.name

the file name of the output video (e.g. ‘animation.mp4’ or ‘animation.avi’)

img.name

the file name of the sequence of images to be generated

ffmpeg

the command to call FFmpeg (e.g. 'C:/Software/ffmpeg/bin/ffmpeg.exe' under Windows or 'avconv' on some linux machines); note the full path of FFmpeg can be pre-specified in ani.options('ffmpeg')

other.opts

other options to be passed to ffmpeg, e.g. we can specify the bitrate as other.opts = '-b 400k' (The default "-pix_fmt yuv420p" is a work-around for a bug in some versions of ffmpeg.)

...

other arguments to be passed to ani.options

Value

An integer indicating failure (-1) or success (0) of the converting (refer to system).

Details

This function uses system to call FFmpeg to convert the images to a single video. The command line used in this function is:

ffmpeg
-y -r <1 interval=""> -i %d. other.opts video.name

where interval comes from ani.options('interval'), and ani.type is from ani.options('ani.type'). For more details on the numerous options of FFmpeg, please see the reference.

Some linux systems may use the alternate software 'avconv' instead of 'ffmpeg'. The package will attempt to determine which command is present and set ani.options('ffmpeg') to an appropriate default value. This can be overridden by passing in the ffmpeg argument.

References

http://ffmpeg.org/documentation.html

Examples

Run this code

oopts = if (.Platform$OS.type == "windows") {
    ani.options(ffmpeg = "D:/Installer/ffmpeg/bin/ffmpeg.exe")
}
## usually Linux users do not need to worry about the ffmpeg path as long as
## FFmpeg or avconv has been installed

saveVideo({
    par(mar = c(3, 3, 1, 0.5), mgp = c(2, 0.5, 0), tcl = -0.3, cex.axis = 0.8, 
        cex.lab = 0.8, cex.main = 1)
    ani.options(interval = 0.05, nmax = 300)
    brownian.motion(pch = 21, cex = 5, col = "red", bg = "yellow")
}, video.name = "BM.mp4", other.opts = "-pix_fmt yuv420p -b 300k")
# higher bitrate, better quality

ani.options(oopts)

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