R/ffmpeg_exec.R

In seankross/ari: Automated R Instructor

#' Get Path to ffmpeg Executable
#'
#' @return The path to the \code{ffmpeg} executable, or an error.
#' @note This looks using `Sys.getenv("ffmpeg")` and `Sys.which("ffmpeg")`
#' to find `ffmpeg`.  If `ffmpeg` is not in your PATH, then please set the
#' path to `ffmpeg` using `Sys.setenv(ffmpeg = "/path/to/ffmpeg")`
#' @param quote should \code{\link{shQuote}} be run before returning?
#' @export
#'
#' @examples
#' \dontrun{
#' if (have_ffmpeg_exec()) {
#'   ffmpeg_exec()
#' }
#' }
ffmpeg_exec <- function(quote = FALSE) {
  ffmpeg <- discard(c(
    Sys.getenv("ffmpeg"),
    Sys.which("ffmpeg")
  ), ~ nchar(.x) == 0)[1]

  if (is.na(ffmpeg)) {
    stop(paste(
      "Could not find ffmpeg. See the documentation ",
      "for ari_stitch() ",
      "for more details."
    ))
  }
  if (!ffmpeg %in% c("ffmpeg", "ffmpeg.exe")) {
    ffmpeg <- normalizePath(ffmpeg, winslash = "/")
  }
  if (quote) {
    ffmpeg <- shQuote(ffmpeg)
  }
  return(ffmpeg)
}

#' @export
#' @rdname ffmpeg_exec
have_ffmpeg_exec <- function() {
  exec <- try(
    {
      ari::ffmpeg_exec()
    },
    silent = TRUE
  )
  !inherits(exec, "try-error")
}

#' Check error output from individual video
#'
#' @return The output of the error log
#' @param file path to video
#' @param verbose print diagnostic messages
#' @export
#'
ffmpeg_error_log <- function(file, verbose = TRUE) {
  ffmpeg <- ffmpeg_exec(quote = TRUE)

  file <- normalizePath(file, winslash = "/", mustWork = TRUE)
  error_file <- tempfile(fileext = ".txt")
  command <- paste(
    ffmpeg, "-v error",
    "-i", shQuote(file),
    paste0("-f null - 2>", error_file)
  )

  if (verbose > 0) {
    message(command)
  }
  res <- system(command)
  if (!file.exists(error_file)) {
    stop("Error file not generated")
  }
  return(readLines(error_file))
}