Backend MP4 conversion (#23)

* ADD conversion queue

* ADD RemuxService for MP4 conversion

* REMOVE unused conversion queue

* REORGANISE Job-related classes

* ADD Job stages

* REVERT to old commit, using Spring Async instead

* ADD asynchronous processing for video tasks

* PATCH and streamline progress tracking

* ADD asynchronous video processing and job restructuring

* REFACTOR job service method

* ADD job remux functionality

* ADD remuxing endpoint

* PATCH complete flag not updating in API response

* ADD progress type in frontend

* ADD reset functionality for job status

* PATCH missing progress bar for subsequent exports

* REDESIGN settings box

* ADD tracking video file conversion in frontend

* PATCH extension bug

* REMOVE autowired decorator

src/main/java/com/ddf/vodsystem/services/media/RemuxService.java

@@ -0,0 +1,46 @@
+package com.ddf.vodsystem.services.media;
+
+import com.ddf.vodsystem.dto.CommandOutput;
+import com.ddf.vodsystem.dto.ProgressTracker;
+import org.springframework.scheduling.annotation.Async;
+import org.springframework.stereotype.Service;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+@Service
+public class RemuxService {
+    private final Pattern timePattern = Pattern.compile("out_time_ms=(\\d+)");
+
+    @Async("ffmpegTaskExecutor")
+    public CompletableFuture<CommandOutput> remux(File inputFile,
+                                                  File outputFile,
+                                                  ProgressTracker remuxProgress,
+                                                  float length
+    ) throws IOException, InterruptedException {
+        List<String> command = List.of(
+                "ffmpeg",
+                "-progress", "pipe:1",
+                "-y",
+                "-i", inputFile.getAbsolutePath(),
+                "-c:v", "h264",
+                "-c:a", "aac",
+                "-f", "mp4",
+                outputFile.getAbsolutePath()
+        );
+
+        return CompletableFuture.completedFuture(CommandRunner.run(command, line -> setProgress(line, remuxProgress, length)));
+    }
+
+    private void setProgress(String line, ProgressTracker progress, float length) {
+        Matcher matcher = timePattern.matcher(line);
+        if (matcher.find()) {
+            float timeInMs = Float.parseFloat(matcher.group(1)) / 1000000f;
+            progress.setProgress(timeInMs / length);
+        }
+    }
+}