Why Won’t My Video Play? Simple Fixes That Work
A video that plays perfectly on one device can refuse to open on another. It is rarely broken. Usually the device simply does not understand the way the video was saved. Here is how to work out what is wrong and fix it.
Containers and codecs, explained simply
Think of a video file as a lunchbox. The box is the container: MP4, MOV, MKV, AVI or WEBM, which is the part you see at the end of the file name. Inside are the foods: the picture and the sound, each packed in a particular way called a codec, such as H.264, HEVC or VP9 for pictures and AAC or MP3 for sound.
A device needs to open the box and understand every food inside. A TV might open an MKV box but not understand the HEVC picture inside it. That is why the same file type can play one day and fail the next.
Problem: “Format not supported” or the file will not open
The device does not understand the container or the codec. The most reliable fix is to change the video to MP4 with H.264 picture and AAC sound, the combination nearly every device supports. Our Video to MP4 tool does this for you, on your own device.
Problem: sound but no picture (black screen)
The device understands the sound but not the picture codec. This often happens with iPhone videos recorded in HEVC played on older Windows computers. Converting to MP4 usually fixes it. For future recordings, set your iPhone to Settings → Camera → Formats → Most Compatible.
Problem: picture but no sound
- Check the obvious first: volume, mute switch, and that the right speakers or headphones are selected.
- The sound may use a codec the device does not support, common with MKV files from films. Converting to MP4 changes the sound to AAC.
- Some screen recordings never had sound. If you recorded your screen, check that microphone or system audio was switched on.
Problem: the website will not accept my upload
- Check the file type: most websites prefer MP4.
- Check the size limit: email usually allows about 20–25 MB, and many forms allow even less.
- Check the length: some platforms limit how many minutes a video can be.
- Try a different browser, or upload over Wi-Fi instead of mobile data.
Problem: it plays, but stutters or freezes
Very high quality videos, such as 4K at 60 frames per second, need a powerful device to play smoothly. Older laptops and phones struggle. Playing the video in a different app, closing other programs, or using a smaller version of the video usually helps.
Only need the sound?
If you only care about what was said or played, for example a lecture or a voice message, turning the video into an MP3 avoids all of these problems. MP3 files are small and play on every device. Our Video to MP3 tool does it in a few seconds.