Video File Won't Play: Fix No Sound in MKV, MOV & Other Formats
Why your video file won't play or has no sound
When a video file opens but plays without sound, or refuses to play altogether, the cause is almost always a missing or incompatible codec. Video files like MKV and MOV are container formats—they wrap video and audio streams that were encoded with specific codecs, and your media player needs the matching decoder to unwrap them. If your player recognizes the video codec but not the audio codec, you see picture without sound. If it recognizes neither, the file won't open.
A secondary cause is file corruption during download or transfer, which can damage the header information or stream data. Less commonly, your player software may be outdated or configured to mute certain tracks.
Check which codec your file actually uses
Before trying fixes, identify what you're dealing with. Right-click the file in Windows and choose Properties > Details, or use a tool like MediaInfo (free, cross-platform). Look for:
- Video codec: H.264, H.265/HEVC, VP9, etc.
- Audio codec: AAC, MP3, AC3, DTS, FLAC, Opus, etc.
MKV files often use FLAC or DTS audio, which many default players don't support. MOV files from iPhones recorded in HEVC mode pair H.265 video with AAC audio—older Windows installations lack HEVC decoders.
Fix: Install the missing codec or use a different player
For Windows 10/11 users with MKV or MOV files that have no sound:
- Install VLC media player (videolan.org)—it includes nearly every common codec and handles MKV, MOV, MP4, and AVI without additional downloads.
- Alternatively, install the K-Lite Codec Pack (codecguide.com) to add codec support system-wide, enabling Windows Media Player and other apps to play the files.
- For HEVC/H.265 video specifically, purchase the official HEVC Video Extensions from the Microsoft Store (£0.99 / $0.99), or install the free community build from GitHub (search "HEVC Video Extensions from Device Manufacturer").
For macOS users:
MOV files should play natively in QuickTime, but MKV files require VLC or IINA (free alternative). If a MOV file recorded on another device won't play, the audio codec may be unsupported—VLC will handle it.
For Android/iOS:
Install VLC for Mobile from the app store. Default gallery apps support limited codecs.
Fix: Repair or re-download corrupted files
If VLC shows an error like "main stream error: no suitable demux module" or the file plays with glitches, the file itself may be damaged. Try:
- Re-download the file from the original source.
- In VLC, go to Tools > Preferences > Input/Codecs and change "Damaged or incomplete AVI file" to Always fix. This sometimes recovers playable video from broken containers.
- Use a repair tool like Stellar Repair for Video (paid) or Treasured (free, limited) for serious corruption.
This is a workaround, not a cure—if the data is genuinely lost, no tool will restore it.
Fix: Update your media player and system
Outdated software often lacks modern codec support. Update:
- VLC: Check Help > Check for Updates.
- Windows Media Player: Run Windows Update to get the latest codecs.
- macOS QuickTime: Update macOS itself, as QuickTime updates come bundled.
On Windows, older versions (7, 8.1) may never support HEVC natively—you'll need third-party software or codec packs.
Workaround: Convert the file to a widely supported format
If you cannot install codecs (e.g., on a locked work computer), converting the file to MP4 with H.264 video and AAC audio ensures compatibility with nearly every device and player. Use HandBrake (free, open-source) or FFmpeg for local conversion without uploading your file anywhere.
This doesn't fix the root problem—it creates a new file your system can decode. The original remains unplayable until you install the correct codec.
FAQ
Why does the video play on my phone but not my computer?
Mobile players like VLC for Android include more codecs by default than Windows Media Player or QuickTime. Your phone can decode the audio stream; your computer cannot. Install VLC on the computer or convert the file.
Can I fix "codec not supported" errors without downloading anything?
No. The error means your system lacks the decoder library needed to interpret the file's data. You must either install the codec, use a player that bundles it, or convert the file to a format your existing software supports.
Will renaming the file extension from MKV to MP4 make it play?
No. Changing the extension does not change the internal encoding. Your player will either reject the file or fail to read it correctly. The container format and codec must actually match what the player expects.
When to convert instead of troubleshooting
If you need the file to work across multiple devices—phones, smart TVs, older laptops—converting once to a universal format saves repeated codec hunts. A service like OmniDesk handles conversions in the browser and supports a wide range of video and audio formats, which is faster than diagnosing codec issues on every device. For files you only play on one machine, installing VLC is simpler.