Four video formats your browser can't play properly. With the extension installed, each one plays with sound.
Install: Chrome Web Store or build from source
Compare: flip the toolbar toggle and refresh to see the browser's own playback. The first video loads the FFmpeg engine (~32 MB, cached afterwards).
Silent without it. The most common broken MKV: DVD and Blu-ray rips. Video is copied untouched, only the audio converted.
Silent without it. The other big "plays, no sound" codec. Same treatment: DTS converted to AAC as it plays.
Silent without it. "DDP 5.1" in release names. The six-channel track becomes 5.1 AAC, surround preserved.
Nothing plays without it. The classic 2000s rip: Chromium can't open AVI at all. Both streams are transcoded live.
With the extension on, these open in the full-page player instead of downloading. You can also right-click one → "Play link with AbsolutePlayer".