Error initializing complex filters. Invalid argument error when running ffmpeg from Kotlin

Question

I'm creating a wrapper for ffmpeg, and it has the following methods:

fun executeCommand(args: Array<String>): AppRunner.AppResult {
    return appRunner.run(ffmpegPath, args)
}


class AppRunner {

    fun run(
        app: String,
        args: Array<String>,
        timeoutAmount: Long = 60000,
        timeoutUnit: TimeUnit = TimeUnit.SECONDS
    ): AppResult {
        val command = mutableListOf(app)
        command.addAll(args)

        val processResult = ProcessBuilder(command)
            .redirectOutput(ProcessBuilder.Redirect.PIPE)
            .redirectError(ProcessBuilder.Redirect.PIPE)
            .start()
            .apply {
                waitFor(timeoutAmount, timeoutUnit)
            }

        val exitCode = processResult.exitValue()
        val stdOut = processResult.inputStream.bufferedReader().readText()
        val stdErr = processResult.errorStream.bufferedReader().readText()

        return AppResult(exitCode, stdOut, stdErr)
    }

}

And:

fun concatenateAudioFiles(files: Collection<File>, outFile: File) {
    val args = mutableListOf<String>()

    files.forEach { file ->
        args.add("-i")
        args.add(file.absolutePath)
    }

    // Create filter
    val filterStringBuilder = StringBuilder()
    filterStringBuilder.append("'")
    files.forEachIndexed { index, _ ->
        filterStringBuilder.append("[$index:0]")
    }
    filterStringBuilder.append("concat=n=")
    filterStringBuilder.append(files.size)
    filterStringBuilder.append(":v=0:a=1[out]")
    filterStringBuilder.append("'")

    args.add("-filter_complex")
    args.add(filterStringBuilder.toString())
    args.add("-map")
    args.add("'[out]'")
    args.add(outFile.absolutePath)
    logger.info { "Filter: ${args.joinToString(" ")}" }
    val result = executeCommand(args.toTypedArray())
    if (!result.isSuccessful()) {
        throw FfmpegException(result.toString())
    }
}

Args generated by this method are OK:

-i silence-0.5.mp3 -i vo_1543189276830.mp3 -i silence-0.5.mp3 -filter_complex '[0:0][1:0][2:0]concat=n=3:v=0:a=1[out]' -map '[out]' vo_final_1543189276833.mp3

And if I run ffmpeg with this args from command line it works fine.

But when running within Kotlin app, it gives the following error:

[AVFilterGraph @ 0x7fd134071500] No such filter: '[0:0][1:0][2:0]concat=n=3:v=0:a=1[out]'
Error initializing complex filters.
Invalid argument

I've already tried to:

1. Check similar questions
2. Escape ' with \
3. Replace ' with "

Result is the same.

FFMPEG 4.1, Kotlin 1.3, Java 1.8, macOS 10.13.6

Answer 1

Well, the solution is to remove ' at all:

fun concatenateAudioFiles(files: Collection<File>, outFile: File) {
    val args = mutableListOf<String>()

    files.forEach { file ->
        args.add("-i")
        args.add(file.absolutePath)
    }

    // Create filter
    val filterStringBuilder = StringBuilder()
    files.forEachIndexed { index, _ ->
        filterStringBuilder.append("[$index:0]")
    }
    filterStringBuilder.append("concat=n=")
    filterStringBuilder.append(files.size)
    filterStringBuilder.append(":v=0:a=1[out]")

    args.add("-filter_complex")
    args.add(filterStringBuilder.toString())
    args.add("-map")
    args.add("[out]")
    args.add(outFile.absolutePath)
    logger.info { "Filter: ${args.joinToString(" ")}" }
    val result = executeCommand(args.toTypedArray())
    if (!result.isSuccessful()) {
        throw FfmpegException(result.toString())
    }
}

I'm sure that happens because ProcessBuilder escapes arguments with ", so they looked like "-filter_complex" "'[0:0][1:0][2:0]concat=n=3:v=0:a=1[out]'", and that's wrong.