Adds a Letterbox cropper, and fixes cover images for the anime converter

Adds a new letterbox cropper, which will use 10 samples at 30 points in a video in order to find the correct crop to remove letter-boxing.
Makes sure to always copy codec of cover images, as ffmpeg treats them as video streams.

src/main/java/net/knarcraft/ffmpegconverter/utility/FFMpegHelper.java

@@ -33,40 +33,6 @@ public final class FFMpegHelper {
     private FFMpegHelper() {
 
     }
-    
-    /*
-    Developer notes:
-      Setting the default track:
-        -disposition:s:0 +default
-        Where s,a,v is the type specifier, and the number is the relative index
-        
-        To unset default:
-        -disposition:s:0 -default
-    
-      -map command for reordering:
-          First number is the index of the input file, which is 0, unless more files are given as input
-          Optionally, a,v,s can be used to select the type of stream to map
-          Lastly, the number is either the global index of the stream, or the relative, if a type has been specified
-          If only the first number is given, all streams from that file are selected
-          The output file will contain all mapped streams in the order they are mapped
-          
-          Plan: Sort all streams by set criteria. Map all selected streams by looping using their relative index for
-          selection.
-       
-      Streams should probably have an input index, so it's easier to treat extra subtitles more seamlessly. So, by
-      including any external subtitle files as input, there would be no need to fiddle more with storing input files.
-      
-      Instead of storing the ffmpeg command as a list of strings, it should be stored as an object with different list
-      for input arguments and output arguments. That way, it would be much easier to add input-related arguments later
-      in the process.
-      
-      ffmpeg -codecs:
-        Used for checking which codecs are available.
-      
-      ffmpeg -h encoder=h264_nvenc:
-        Used to see available encoder presets/profiles/info
-      
-     */
 
     /**
      * Gets streams from a file
@@ -280,6 +246,29 @@ public final class FFMpegHelper {
         return StringUtil.stringBetween(result.output(), "[STREAM]", "[/STREAM]");
     }
 
+    /**
+     * Gets the duration, in seconds, of the given file
+     *
+     * @param ffprobePath <p>The path to the ffprobe executable</p>
+     * @param file        <p>The file to get the duration of</p>
+     * @return <p>The duration</p>
+     * @throws IOException           <p>If unable to probe the file</p>
+     * @throws NumberFormatException <p>If ffmpeg returns a non-number</p>
+     */
+    public static double getDuration(@NotNull String ffprobePath, @NotNull File file) throws IOException, NumberFormatException {
+        FFMpegCommand probeCommand = new FFMpegCommand(ffprobePath);
+        probeCommand.addGlobalOption("-v", "error", "-show_entries", "format=duration", "-of",
+                "default=noprint_wrappers=1:nokey=1");
+        probeCommand.addInputFile(file.toString());
+
+        ProcessBuilder processBuilder = new ProcessBuilder(probeCommand.getResult());
+        ProcessResult result = runProcess(processBuilder, file.getParentFile(), "", false);
+        if (result.exitCode() != 0) {
+            throw new IllegalArgumentException("File probe failed with code " + result.exitCode());
+        }
+        return Double.parseDouble(result.output().trim());
+    }
+
     /**
      * Takes a list of all streams and parses each stream into one of three objects
      *
@@ -294,7 +283,8 @@ public final class FFMpegHelper {
     private static StreamProbeResult parseStreams(@NotNull String ffprobePath, @NotNull List<String> streams,
                                                   @NotNull File file, @NotNull List<String> subtitleFormats,
                                                   @NotNull List<String> audioFormats) throws IOException {
-        StreamProbeResult probeResult = new StreamProbeResult(new ArrayList<>(List.of(file)), parseStreamObjects(streams));
+        StreamProbeResult probeResult = new StreamProbeResult(new ArrayList<>(List.of(file)),
+                parseStreamObjects(streams));
         getExternalStreams(probeResult, ffprobePath, file.getParentFile(), file.getName(), subtitleFormats);
         getExternalStreams(probeResult, ffprobePath, file.getParentFile(), file.getName(), audioFormats);
         return probeResult;
@@ -319,18 +309,11 @@ public final class FFMpegHelper {
             StreamType streamType = getStreamType(streamInfo);
 
             switch (streamType) {
-                case VIDEO:
-                    parsedStreams.add(new VideoStream(streamInfo, 0, relativeVideoIndex++));
-                    break;
-                case AUDIO:
-                    parsedStreams.add(new AudioStream(streamInfo, 0, relativeAudioIndex++));
-                    break;
-                case SUBTITLE:
-                    parsedStreams.add(new SubtitleStream(streamInfo, 0, relativeSubtitleIndex++));
-                    break;
-                case OTHER:
-                    parsedStreams.add(new OtherStream(streamInfo, 0));
-                    break;
+                case VIDEO -> parsedStreams.add(new VideoStream(streamInfo, 0, relativeVideoIndex++));
+                case AUDIO -> parsedStreams.add(new AudioStream(streamInfo, 0, relativeAudioIndex++));
+                case SUBTITLE -> parsedStreams.add(new SubtitleStream(streamInfo, 0, relativeSubtitleIndex++));
+                case OTHER -> parsedStreams.add(new OtherStream(streamInfo, 0, false));
+                case COVER_IMAGE -> parsedStreams.add(new OtherStream(streamInfo, 0, true));
             }
         }
         return parsedStreams;
@@ -347,11 +330,13 @@ public final class FFMpegHelper {
         String codecType = ValueParsingHelper.parseString(streamInfo.get(StreamTag.CODEC_TYPE), "");
         switch (codecType) {
             case "video":
+                String mime = ValueParsingHelper.parseString(streamInfo.get(StreamTag.TAG_MIME_TYPE), "");
                 // Some attached covers are marked as video streams
-                if (ValueParsingHelper.parseInt(streamInfo.get(StreamTag.DISPOSITION_ATTACHED_PIC), 0) != 1) {
+                if (ValueParsingHelper.parseInt(streamInfo.get(StreamTag.DISPOSITION_ATTACHED_PIC), 0) != 1 &&
+                        !mime.startsWith("image/") && !mime.endsWith("-font")) {
                     return StreamType.VIDEO;
                 } else {
-                    return StreamType.OTHER;
+                    return StreamType.COVER_IMAGE;
                 }
             case "audio":
                 return StreamType.AUDIO;

src/main/java/net/knarcraft/ffmpegconverter/utility/StringUtil.java

@@ -8,7 +8,7 @@ import java.util.List;
 /**
  * A class which helps with operations on strings
  */
-final class StringUtil {
+public final class StringUtil {
 
     private StringUtil() {