R/concat.R

In compost: Video Compositing via 'FFmpeg'

#' Concatenate Video Segments
#'
#' Join multiple video files sequentially using FFmpeg's concat demuxer.
#' All inputs should have compatible codecs and dimensions.
#'
#' @param inputs Character vector of paths to input video files.
#' @param output Path for output video file.
#' @param overwrite If TRUE (default), overwrite output file.
#' @param dry_run If TRUE, return the FFmpeg command without executing.
#'
#' @return Invisibly returns the output path. If dry_run, returns command string.
#'
#' @examples
#' \dontrun{
#' concat(c("part1.mp4", "part2.mp4", "part3.mp4"), "full.mp4")
#' }
#'
#' @export
concat <- function(inputs, output, overwrite = TRUE, dry_run = FALSE) {
    if (length(inputs) < 2) {
        stop("concat() requires at least 2 inputs", call. = FALSE)
    }

    inputs <- normalizePath(inputs, mustWork = TRUE)
    output <- normalizePath(output, mustWork = FALSE)

    # Write concat list to temp file. Forward-slash the paths: the concat demuxer
    # treats backslash as an escape character inside a quoted path, so a Windows
    # path like C:\Users\... would be mangled. ffmpeg accepts / on Windows.
    concat_list <- tempfile(fileext = ".txt")
    on.exit(unlink(concat_list), add = TRUE)
    writeLines(paste0("file '", gsub("\\\\", "/", inputs), "'"), concat_list)

    args <- c(if (overwrite) "-y", "-f", "concat", "-safe", "0", "-i",
              concat_list, "-c", "copy", output)

    if (dry_run) {
        return(.run_ffmpeg(args, dry_run = TRUE))
    }
    .run_ffmpeg(args)
    invisible(output)
}