命令适用于终端，但不适用于 Kotlin

Question

I'm trying to use an FFMPEG command for concatenating different videos. The command is

ffmpeg -i video.mp4 -i video-2.mp4 -filter_complex "[0:v:0] [0:a:0] [1:v:0] [1:a:0] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4

This command works good when I run on Windows PowerShell. But when I try to run with Kotlin code it doesn't work.

val firstVideo = "D:\\Videos\\ffmpeg\\video.mp4"
val secondVideo = "D:\\Videos\\ffmpeg\\video-2.mp4"
val resultPath = "D:\\Videos\\ffmpeg\\result-2.mp4"

val cmd = "ffmpeg -i $firstVideo -i $secondVideo -filter_complex \"[0:v:0] [0:a:0] [1:v:0] [1:a:0] concat=n=2:v=1:a=1 [v] [a]\" -map \"[v]\" -map \"[a]\" $resultPath"
.split(" ").toTypedArray()

Runtime.getRuntime().exec(cmd)

I'm not taking any error messages since I'm using FFMPEG cli.

Also, this piece of Kotlin works perfect when I'm trying to run other FFMPEG operations.

Answer 1

Turns out the actual issue was within the Runtime.getRuntime().exec() function. I tried to call waitFor() method but it got stuck. I was waiting forever. I did some research and read the docs.

Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, or even deadlock.

This code was works just fine:

fun main(){

   val path1 = "video-1.mp4"
   val path2 = "video-2.mp4"
   val resultPath = "output.mp4"

   val cmd = arrayOf("ffmpeg",
    "-i", path1, "-i", path2,
    "-filter_complex", "[0:v:0][0:a:0][1:v:0][1:a:0]concat=n=2:v=1:a=1[v][a]",
    "-map", "[v]", "-map", "[a]", resultPath)

    executeCommand(cmd)
}

fun executeCommand(cmd: Array<String>){
    try {
       val runtime = Runtime.getRuntime()
       val process = runtime.exec(cmd)
       val errorStream = process.errorStream
       val input = InputStreamReader(errorStream)
       val reader = BufferedReader(input)
       reader.forEachLine {
          println(it);
       }
       process.waitFor()
   } catch (e: Exception) {
       e.printStackTrace();
   }
}

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https://www.javaworld.com/article/2071275/when-runtime-exec---won-t.html

https://docs.oracle.com/javase/8/docs/api/java/lang/Process.html