Macos Sierra QuickTime no video just sound Hi, I found that QuickTime player doesn't play mp4 videos after I updated macOS Sierra. I can hear only sound. Codec of video is h.264 and sound AAC. Does anybody have the same problem or have any ideas how to fix it? I have the same problem on MacBook Air HD5000. VLC player can play the MP4 file but QT doesn't. Even my iMac with Sierra can play it ...