feat: 음성파일 병합 및 병합 시 파일 간 간격 지정에 사용되는 Ffmpeg 사용 기능 구현

src/main/kotlin/com/sangdol/text_to_speech/FfmpegUtils.kt

@@ -0,0 +1,94 @@
+package com.sangdol.text_to_speech
+
+import net.bramp.ffmpeg.FFmpeg
+import net.bramp.ffmpeg.FFmpegExecutor
+import net.bramp.ffmpeg.builder.FFmpegBuilder
+import org.springframework.stereotype.Component
+import java.io.File
+
+private const val FFMPEG_PATH: String = "/opt/homebrew/bin/ffmpeg"
+private const val SILENCE_AUDIO_PATH: String = "library/silences"
+
+private fun convertSilenceAudioFilePath(durationMs: Long) = "$SILENCE_AUDIO_PATH/silence-${durationMs}ms.mp3"
+
+@Component
+class FfmpegUtils(
+    private val ffmpegExecutor: FFmpegExecutor = FFmpegExecutor(FFmpeg(FFMPEG_PATH))
+) {
+
+    fun createSilenceAudio(durationMs: Long) {
+        val durationSeconds = durationMs / 1000.0
+        val outputFile = convertSilenceAudioFilePath(durationMs)
+
+        val command = listOf(
+            FFMPEG_PATH,
+            "-y",
+            "-f", "lavfi",
+            "-i", "anullsrc=r=44100:cl=stereo",
+            "-t", durationSeconds.toString(),
+            "-acodec", "mp3",
+            outputFile
+        )
+
+        val process = ProcessBuilder(command)
+            .redirectErrorStream(true)
+            .start()
+
+        process.inputStream.bufferedReader().forEachLine { println(it) }
+        process.waitFor()
+            .takeUnless { exitCode -> exitCode == 0 }
+            ?: throw RuntimeException("FFmpeg failed with exit code ${process.exitValue()}")
+    }
+
+    fun mergeAudioWithInterval(intervalMs: Long, targetDirectory: String, saveDirectory: String, fileName: String) {
+        val targetDir = File(targetDirectory).also { validateIsValidFileDirectory(it) }
+        val fileNameRegex = """(\d+)(.*)""".toRegex()
+
+        if (intervalMs > 0 && !File(convertSilenceAudioFilePath(intervalMs)).exists()) {
+            createSilenceAudio(intervalMs)
+        }
+
+        val files = targetDir.listFiles().sortedBy { it ->
+            val matchResult: MatchResult = fileNameRegex.find(it.name)
+                ?: throw IllegalStateException("Invalid filename-convention")
+            matchResult.groups[1]!!.value.toInt()
+        }.map { "$it" }
+
+        val inputs = mutableListOf<String>()
+        files.forEachIndexed { idx, file ->
+            inputs.add(file)
+            if (intervalMs > 0L && (idx != files.lastIndex)) {
+                inputs.add("library/silences/silence-${intervalMs}ms.mp3")
+            }
+        }
+
+        val builder = FFmpegBuilder()
+
+        inputs.forEach { filePath -> builder.addInput(filePath) }
+
+        val filterInputs = inputs.indices.joinToString("") { idx -> "[$idx:a]" }
+        val filterComplex = "$filterInputs concat=n=${inputs.size}:v=0:a=1[out]"
+
+        builder.setComplexFilter(filterComplex)
+            .addOutput("$saveDirectory/$fileName")
+            .setAudioCodec("mp3")
+            .addExtraArgs("-map", "[out]")
+            .done()
+
+        ffmpegExecutor.createJob(builder).run()
+    }
+
+    private fun validateIsValidFileDirectory(dir: File) {
+        if (!dir.exists()) {
+            throw IllegalArgumentException("Directory not found: $dir")
+        }
+        if (!dir.isDirectory) {
+            throw IllegalArgumentException("Path is not a directory: $dir")
+        }
+        val fileList = dir.listFiles()
+
+        if (fileList == null || fileList.isEmpty()) {
+            throw IllegalArgumentException("Directory is null or empty: $dir")
+        }
+    }
+}