Some H.264 stream in MKV container is already iPhone or iPad playable. In such case, we only need to convert the audio format and remux the video stream with converted audio stream into MP4 container in order to let iPhone or iPad play it. This can save us significant amount of time for transcoding.

现在很多网上下载的MKV文件的视频流已经是可以直接被iPhone或者iPad解码的，在这种情况下要把文件转换为iPhone或者iPad可以播放的MP4文件就没有必要转换视频部分，只要将音频部分转码，然后和原始的视频流混合成iPhone/iPad支持的MP4格式即可。