Why do downloaded videos have no sound?

Streams are stored separately now

A decade ago a video file was one file: picture and sound muxed together. Modern streaming platforms split them. The player in your browser requests a video stream and an audio stream separately and plays them in sync — which lets the platform switch video quality mid-playback without touching the audio. Great for streaming; a trap for downloading. If a tool grabs only the video stream — the obvious one — the saved file is silent, because the sound was never in it.

Reddit is the classic case

Reddit-hosted video is the place almost everyone meets this problem: the video lives at one URL and the audio at another, and the “copy video address” trick gets you the silent half. YouTube does the same at resolutions above 720p (its combined format tops out there — every higher resolution is video-only plus a separate audio stream). Instagram, TikTok and X mostly serve combined files, which is why the silent-download problem feels platform-specific.

The proper fix: server-side merging

The correct solution is to download both streams and mux them — combine them into one container — using ffmpeg. Muxing is lossless and fast (no re-encoding; the streams are copied into one MP4). That is exactly what Simple Video Downloader’s processing server does on every download that needs it: fetch video, fetch audio, merge, deliver one normal MP4 with sound. It is the whole reason the Reddit downloader leads with “videos with sound” — and the same server-side merge is what the YouTube downloader uses for anything above 720p.

If you already have a silent file

Work through it in order. Downloaded video has no audio covers the same checks as a step-by-step troubleshooter.

1. Re-download with a merging tool

   One that fetches both streams and muxes them — that is the reliable fix, and it hands you one MP4 with sound.

2. Captured the video and audio as two separate files yourself?

   Join them losslessly with ffmpeg: ffmpeg -i video.mp4 -i audio.m4a -c copy output.mp4

3. Silent only on a TV or older device?

   That is usually a codec issue rather than a missing track (more below), so keep the file as MP4 with AAC audio.

4. If the original post genuinely has no audio

   Some do — and no tool can add sound that was never recorded.

One more silent-video culprit

Avoiding it next time

Use a downloader that merges streams server-side and hands you MP4 with AAC audio, and choose that MP4 output rather than a video-only stream. That is the default here — which is why downloads arrive with sound and play on any device, with no ffmpeg and no second step.