code: function rewriteDuration() {
                  var
                      buffer = new ArrayBufferDataStream(8),
                      oldPos = blobBuffer.pos;
                  
                  // Rewrite the data payload (don't need to update the id or size)
                  buffer.writeDoubleBE(clusterStartTime);
                  
                  // And write that through to the file
                  blobBuffer.seek(segmentDuration.dataOffset);
                  blobBuffer.write(buffer.getAsDataArray());
          
                  blobBuffer.seek(oldPos);
              }
docs: Rewrite the Duration field of the Segment with the newly-discovered video duration.