Feature/346 add bf option

src/main/java/net/bramp/ffmpeg/builder/AbstractFFmpegOutputBuilder.java

@@ -67,7 +67,13 @@ public abstract class AbstractFFmpegOutputBuilder<T extends AbstractFFmpegOutput
   @Deprecated
   public String video_bit_stream_filter;
 
-  protected String  complexFilter;
+  /**
+   * Specifies the number of b-frames ffmpeg is allowed to use.
+   * 0 will disable b-frames, null will let ffmpeg decide.
+   */
+  protected Integer bFrames;
+
+  protected String complexFilter;
 
   public AbstractFFmpegOutputBuilder() {
     super();
@@ -120,6 +126,18 @@ public T setVideoPreset(String preset) {
     return (T) this;
   }
 
+  /**
+   * Sets the number of b-frames ffmpeg is allowed to use.
+   * 0 means: Do not use b-frames at all
+   *
+   * @param bFrames number of b-frames
+   * @return this
+   */
+  public T setBFrames(int bFrames) {
+    this.bFrames = bFrames;
+    return (T) this;
+  }
+
   /**
    * Sets Video Filter
    *
@@ -365,6 +383,10 @@ protected void addVideoFlags(FFmpegBuilder parent, ImmutableList.Builder<String>
     if (!Strings.isNullOrEmpty(video_bit_stream_filter)) {
       args.add("-bsf:v", video_bit_stream_filter);
     }
+
+    if (bFrames != null) {
+      args.add("-bf", Integer.toString(bFrames));
+    }
   }
 
   @Override

src/test/java/net/bramp/ffmpeg/builder/AbstractFFmpegOutputBuilderTest.java

@@ -111,4 +111,13 @@ public void testSetComplexFilter() {
 
         assertThat(removeCommon(command), is(ImmutableList.of("-filter_complex", "complex-filter")));
     }
+
+    @Test
+    public void testSetBFrames() {
+        List<String> command = getBuilder()
+                .setBFrames(2)
+                .build(0);
+
+        assertThat(removeCommon(command), is(ImmutableList.of("-bf", "2")));
+    }
 }