Converted MP4 Has No Sound? Here's Why
Your converted MP4 plays but the sound is gone. Usually the track survived and the player cannot decode it — here is how to tell before converting again.
Most silent MP4s are not missing their audio. The track is usually still inside the file in a codec the player refuses to decode — AC-3, E-AC-3 or DTS, all legal in an MP4 container and all unsupported by browsers, most web upload previews and a lot of TV apps — and the fix is to re-encode that track to AAC, not to convert the file again the same way. The second most common cause is the opposite: the converter dropped the audio stream entirely, in which case there is nothing to decode and no setting will bring it back.
On a phone, Convertlix for Android (8.0 or later) does that re-encode on the device: the video is opened through Android's own file picker, the work runs on the phone's own processor, and the result is written to Downloads. Nothing is uploaded, so there is no server copy to retain — its network calls carry sign-in, licence, quota and payment traffic, never media. Sign-in is required once and there is no guest mode; after that the tools run with the network off. Free-tier videos are capped at 100 MB per file, Premium at 2 GB, and the monthly conversion allowance is server-set and shown in the app.
Silence is a symptom with five different causes
You are not imagining the confusion here: the same black-and-quiet result comes from causes that need opposite fixes, and every generic "convert it again" answer picks one at random. Sorted by how often they turn out to be the culprit:
- An audio codec the player cannot decode. The file is intact. A Blu-ray rip, a broadcast recording or an MKV converted to MP4 by a container-only remux keeps its AC-3, E-AC-3 (Dolby Digital Plus) or DTS track. Chrome, Firefox and Safari ship no AC-3 or DTS decoder, and neither do many browser-based upload previews. The picture plays because H.264 is decoded fine; the audio silently fails.
- The audio stream was dropped during conversion. Some converters and trimmers write video only, either by default or because the source audio codec was not supported as an input. The output has one track where the source had two.
- The source was video-only. Screen recorders started without a mic or audio-capture permission, GIF-derived clips, drone footage, security-camera exports and time-lapses often carry no audio track at all. Nothing downstream can invent one.
- The track is there and playing, at zero. A per-app volume, a muted media stream, a Bluetooth device still holding the audio route, or a source recorded with the mic covered. Cheap to rule out, and worth ruling out first.
- The audio is on a second track the player ignores. MKVs commonly carry two or three audio tracks — a commentary, a dub, a stereo downmix. A conversion that keeps only the first track can keep the wrong one, and some players default to track 1 regardless of the default flag.
What you can fix is 1, 2 and 5: those are codec and stream problems, and re-encoding the audio to AAC solves all three. What no tool fixes is 3. If the source genuinely has no audio track, every converter, app and website will hand back a silent file, and a page telling you otherwise is wrong.
Diagnose it before you convert again
The whole point of this step is that converting again with the same settings reproduces the same silence. Three checks, in order, and each one eliminates a cause:
Play the source, not the output. Open the original file in your gallery, with the volume up and Bluetooth off. If the source is silent too, you have cause 3 or 4 and the conversion is innocent.
Play the output in two different players. This is the single most informative test on this page. VLC for Android bundles its own decoders, including AC-3, E-AC-3 and DTS; Chrome and the stock Android player do not. If VLC plays the sound and Chrome does not, the audio track exists and the codec is the problem — cause 1, and AAC is the answer. If both are silent, the stream is probably gone — cause 2 or 3.
Read the file size difference. Audio is small next to video but not invisible: an AAC track at 128 kbps is about 1 MB per minute. A ten-minute output that came back 10 MB smaller than a source with the same picture settings lost its audio stream, not its bitrate.
If the source is an MKV, check the track count. VLC's Audio then Audio Track menu lists them. Two or three entries means cause 5 is live.
| Symptom | Likely cause | Fix | What you lose |
|---|---|---|---|
| Silent in a browser, fine in VLC | AC-3, E-AC-3 or DTS track | Re-encode the audio to AAC | One encoding generation; surround is downmixed to stereo |
| Silent in every player, source has sound | Audio stream dropped in conversion | Convert again with a tool that writes an audio track | Time |
| Source is silent too | No audio track was ever recorded | Nothing to recover — re-record if you can | The audio, permanently |
| Wrong language or a commentary track | Multi-track MKV, wrong track kept | Pick the track deliberately on a desktop tool | Time, and the other tracks |
| Plays loud on the phone, silent on the TV | The TV app's decoder, or its own audio route | Re-encode to AAC stereo; check the TV's audio output setting | Surround channels |
Why AAC is the target
AAC at 128 to 256 kbps stereo inside an MP4 is the combination with the broadest decoder support of anything you can produce on a phone: every mainstream browser, Android and iOS, cast receivers, and essentially every web upload form. That is a compatibility argument, not a quality one — AC-3 is not a worse codec, it is a less widely licensed one, and re-encoding it costs you a generation of quality plus the surround channels, which get downmixed to two.
So the trade is real and worth stating: you are giving up 5.1 to get sound at all. On a phone or a laptop with two speakers that costs you nothing you can hear. If the file is destined for a receiver that genuinely decodes Dolby Digital, do not convert it — fix the player instead.
Containers matter here too, because the audio track is only ever as reachable as the container's index makes it. The same anatomy is behind Downloaded Video Won't Seek on Your TV? The Fix, and if what you want is the sound on its own rather than a working video, Extract the Audio From a Video on Android is the shorter road.
How to fix an MP4 with no sound
- Rule out the boring causes. Volume up, media volume specifically, Bluetooth disconnected, headphones out. Then play the original file — if it is silent, stop here, because the conversion is not what broke it.
- Play the converted file in VLC and in Chrome. Sound in VLC but not Chrome means the track is present and the codec is unsupported. Silence in both means the stream is missing and you need a fresh conversion from the source.
- Check the file size. Long-press both files and compare. Over 100 MB is above the free per-video ceiling, so a long recording needs trimming first or Premium, which takes files up to 2 GB.
- Convert the video again from the original, not from the silent copy. In Convertlix that is Video Converter, which takes MP4, MKV, MOV or AVI, writes MP4, MKV, MOV or MP3, and can trim. It runs on the phone, so nothing is uploaded and the new file lands in Downloads beside the original.
- Test the result where it has to work. Not just in your gallery — in the browser, the upload form or the TV app that was silent. Play the middle of the file, not the first two seconds.
- If you need a specific audio track from a multi-track MKV, use a desktop tool. ffmpeg's
-maplets you name the exact stream; a phone tool takes the file as a whole.
When this will not work
A source with no audio track is not recoverable, and that includes most screen recordings made without audio permission and most drone and dashcam footage. DRM-protected downloads from a streaming service are encrypted end to end, so nothing here opens them. Videos over 100 MB are refused on the free tier, and the cap applies to the file you hand over, so a 45-minute 4K recording will not convert on a free account at all — trim it elsewhere first or move to Premium. If you need a particular track out of a three-track MKV, or you want to keep 5.1 while changing only the container, a computer running ffmpeg or HandBrake is genuinely the better tool. And if the audio was recorded badly — clipped, or from across a room — a conversion returns exactly what was captured.
FAQ
Why does my video play but have no sound after converting?
In most cases the audio track is still inside the file, in a codec the player will not decode: AC-3, E-AC-3 (Dolby Digital Plus) and DTS are all valid in an MP4 but have no decoder in Chrome, Firefox, Safari or many TV and upload-preview players. The video decodes fine because H.264 is universally supported, so you get picture and silence. Re-encoding just the audio to AAC fixes it.
How do I tell whether the audio track is missing or just undecodable?
Play the file in VLC for Android, which ships its own AC-3 and DTS decoders, and then in Chrome, which does not. Sound in VLC and silence in Chrome means the track exists and the codec is unsupported. Silence in both, with a source that has sound, means the conversion dropped the audio stream and you should convert again from the original.
What audio format should I convert to?
AAC at 128 to 256 kbps in stereo, inside an MP4. It has the widest decoder support of anything a phone can produce — browsers, Android, iOS, cast receivers and web upload forms all take it. The cost is one encoding generation and the loss of surround channels, which get downmixed to two, so do not do it to a file that a working 5.1 receiver already plays.
Can a converter add sound to a video that has none?
No. If the source has no audio track — a screen recording made without audio permission, drone footage, a time-lapse — there is nothing to decode, and every app and website will return a silent file. What remains is re-recording, or adding a separate audio file in a video editor, which is a different job from conversion.
Does Convertlix upload my video?
No. The video is opened through Android's own file picker, decoded and re-encoded by the phone itself, and the result is written to Downloads, so no copy is sent anywhere and there is nothing on a server to delete. The app's network calls carry sign-in, licence, quota, configuration and payment data only, and it asks for no storage permission. Sign in once, switch on airplane mode, and the conversion still completes.
Can I fix this on a computer instead?
Yes, and for a large file a computer is faster and more precise. ffmpeg re-encodes only the audio and copies the picture untouched in one line — ffmpeg -i in.mp4 -c:v copy -c:a aac -b:a 192k out.mp4 — which avoids a second video generation entirely. HandBrake exposes the same choice in its Audio tab, with a per-track codec picker that a phone tool does not have.
If VLC plays the sound and your browser does not, the track is fine and only its codec is wrong — Video Converter re-encodes it to AAC on the phone and leaves the original file where it is.