Video Plays but No Sound: A Three-Layer Troubleshooting Chain
The video plays fine but silence — before re-encoding anything, locate the layer: truly no audio track, a track the player cannot decode, or playback that is simply muted. Most cases resolve in one minute.
Layer one: rule out the fake-outs
Try another player or device — sound appearing means the original player lacks the decoder or is muted. Check system volume and the browser tab mute (muted tabs are the classic). Headphones on — some devices fail on external speakers or split volume zones. A third of "no sound" cases die here.
Second confirmation: scrub the timeline — silent everywhere or silent in spots? Local silence means the source was recorded or exported without that audio; that is not a playback problem.
Layer two: does the file contain a track at all
Inspect the stream structure with a track tool: an audio stream present means the file has sound — jump to layer three. No audio stream means the file is genuinely silent; walk back the source: screen recording without system-audio capture, an export that stripped the track, a conversion that dropped it — all common accidents.
A truly silent file is not "repaired" but "re-filled": re-export from the original material, or add a replacement track (music, narration) — a picture-only file plus one audio track is a complete deliverable.
Layer three: a track exists but will not decode
Audio stream present, player silent — usually codec compatibility: AC3, DTS and some high-profile AAC variants lack decoders on certain devices and web players. Confirm the codec, then two paths: re-encode to AAC for universality, or switch to a player that handles the codec.
Prevention: ship everything as AAC-in-MP4 — the all-device common denominator. And before sending files to others, play them once on a second device; audio problems caught before sending cost nothing.