Codec Checker
Identify the real codec inside a file by parsing its container structure, not by trusting the file extension.
Convert with this tool
or choose a file from your device — it is processed in this tab and never uploaded
Accepted: MP4, MOV, MKV, WebM, WAV, MP3, FLAC, M4A
Files stay on your device. There is no upload, no queue and no watermark, so a conversion works even with the network switched off after the page has loaded.
Supported formats & processing
| Accepted input | MP4, MOV, MKV, WebM, WAV, MP3, FLAC, M4A |
|---|---|
| Produced output | An inspection report with a downloadable JSON file |
| Processing | Web Audio API + canvas + native JavaScript encoders |
| Upload required | No — the file is read locally and never transmitted |
How to use this tool
- Add the media fileThe container type is identified from its magic bytes, not its extension.
- Read the codec rowFour-character identifiers are translated into codec names.
- Check the container rowIt tells you whether you have MP4, QuickTime, Matroska or something else.
- Note the resolution or sample rateUseful context for judging whether the codec is appropriate.
- Download the JSON reportEverything found is exported.
About this tool
File extensions lie. An .mp4 can contain H.264, HEVC, AV1 or ProRes video; a .m4a can hold AAC or ALAC; an .ogg can carry Vorbis or Opus. The extension describes the container, and the codec inside it is a separate decision that the container records in its own metadata.
This checker reads that metadata directly. For MP4 and MOV it walks the box tree to the stsd sample description entries and reports the four-character codec identifiers. For Matroska and WebM it parses the EBML tree for CodecID elements. For WAV it reads the RIFF format tag, and for MP3 it parses the MPEG frame header for the version and layer.
Features
- MP4 and MOV box walking to the stsd sample entries
- Matroska and WebM EBML parsing for CodecID values
- RIFF format tag decoding for WAV
- MPEG frame header parsing for MP3 version and layer
- Codec identifiers translated into readable names
- Magic-byte container detection that ignores the file extension
Frequently asked questions
What do the four-character codes mean?
avc1 and avc3 are H.264, hvc1 and hev1 are H.265/HEVC, av01 is AV1, vp09 is VP9, mp4a is AAC, alac is Apple Lossless, ac-3 is Dolby AC-3. These are the standard sample entry types defined by the MP4 specification.
Why does my file show two codecs?
A video file has a video stream and an audio stream, each with its own codec. The checker reports both, joined with a plus sign.
Does the codec determine whether a device will play the file?
The codec and the container both matter. An MP4 with H.264 and AAC plays almost anywhere; the same container with HEVC may not play on older hardware, and with ProRes it will not play on consumer devices at all.
How do I convert to a more compatible codec?
Use the video format converter or the MP4 converter, which re-encode to H.264 with AAC audio — the combination with the widest support.