These terms are often mixed up. Understanding the difference makes everything else about audio and video much easier.
Codec: compression
Container: file packaging
Standard: rules or certification
A codec is the technology that encodes and decodes audio or video. It decides how the sound or picture is compressed, stored, and reconstructed for playback.
Examples: H.264, H.265 / HEVC, AV1, AAC, MP3, FLAC, and Opus.
A container format is the file structure that holds one or more streams together. It can package video, audio, subtitles, chapters, artwork, and metadata.
Examples: MP4, MKV, MOV, WebM, WAV, and M4A.
A standard describes how something should be made, decoded, delivered, certified, or played back. Some standards are technical specifications; others are playback or quality systems.
Examples: MPEG-4, ISO Base Media File Format, Dolby Atmos, DTS:X, and THX.
Examples: H.264 video, AV1 video, AAC audio, FLAC audio
Examples: MP4, MKV, MOV, WebM, M4A, WAV
Examples: Dolby Atmos, DTS:X, THX, MPEG standards, device compatibility rules
The codec decides how the ingredients are prepared. For video, that means how frames are predicted and compressed. For audio, that means how sound is represented and reduced in size.
The container holds everything together. A movie file might contain video, multiple audio tracks, subtitles, chapters, cover art, and timing information.
The standard says what equipment should expect and how playback should behave. A theater, TV, streaming app, or soundbar may support some standards but not others.
| Label you see | What it usually is | What it means |
|---|---|---|
| MP4 | Container format | A file package that often holds H.264 or H.265 video plus AAC audio. |
| MKV | Container format | A flexible package often used for movies, subtitles, chapters, and multiple audio tracks. |
| WebM | Container format | A web-friendly container that commonly holds VP9 or AV1 video and Opus audio. |
| H.264 | Video codec / standard | A very common video compression system used in MP4, MOV, and streaming video. |
| AAC | Audio codec | A lossy audio compression format often used in MP4, M4A, streaming, and phones. |
| WAV | Audio file format | A file structure that usually contains uncompressed PCM audio. |
| Dolby Atmos | Immersive audio format / playback standard | A way to describe and play object-based surround sound, usually carried by another audio codec. |
| THX | Certification / quality standard | A playback and quality-control system, not a codec and not a normal media file format. |
A single file extension rarely tells the whole story. A video file is usually a stack of several different things working together.
The outer file package, such as MP4, MKV, MOV, or WebM. This controls how the pieces are stored together.
The moving picture, usually compressed with a video codec such as H.264, H.265, AV1, VP9, or ProRes.
The sound, usually compressed or stored with an audio codec such as AAC, Opus, MP3, FLAC, PCM, Dolby Digital, or DTS.
Subtitles, captions, alternate languages, commentary tracks, chapters, thumbnails, and metadata may also be included.
Your device may support the container but not the codec inside it. For example, a TV might open MP4 files but fail on an MP4 that uses a newer video codec or an unsupported audio codec.
Changing the container is different from changing the codec. Remuxing changes the package without re-encoding. Transcoding re-encodes the media and may reduce quality.
Export menus often mix all three ideas together. You may choose MP4 as the container, H.264 as the video codec, AAC as the audio codec, and a streaming platform standard as the target.
| Example label | Container | Video codec | Audio codec |
|---|---|---|---|
| movie.mp4, H.264, AAC | MP4 | H.264 | AAC |
| movie.mkv, H.265, DTS-HD | MKV | H.265 / HEVC | DTS-HD |
| clip.webm, AV1, Opus | WebM | AV1 | Opus |
| song.m4a, AAC | M4A / MP4-family audio container | None | AAC |
| recording.wav, PCM | WAV | None | PCM audio |
MP4 files often contain H.264 video, but they do not have to. MP4 can also contain H.265 / HEVC, AV1, MPEG-4 Visual, AAC, ALAC, subtitles, and other supported streams.
The container does not automatically decide quality. A high-quality MP4 can look better than a low-quality MKV. Quality mostly depends on the source, codec, bitrate, settings, and number of conversions.
Renaming .mkv to .mp4 does not change the structure inside. Real conversion requires remuxing or transcoding with compatible tools.
Atmos is not a simple file extension. It is an immersive audio system that needs compatible content, a delivery codec, playback software, and hardware that understands it.
| If you are asking... | You are probably talking about... | Example answer |
|---|---|---|
| Why is the file so large? | Codec, bitrate, resolution, duration, or lossless storage | ProRes, WAV, and high-bitrate video make large files because they preserve more data. |
| Why will it not open on my TV? | Container and codec compatibility | The TV may accept MP4 but not the specific video or audio codec inside it. |
| Can I change MKV to MP4 without losing quality? | Remuxing vs transcoding | Sometimes yes, if the streams inside are compatible with MP4. |
| Which setting should I export with? | Container, video codec, audio codec, and target standard | For broad compatibility, MP4 with H.264 video and AAC audio is often the safe choice. |
| Why does it sound or look bad? | Compression settings and source quality | The codec and bitrate matter, but a bad source or repeated conversions can also cause artifacts. |
No. A codec compresses or decompresses the audio or video stream. A format or container packages streams together into a file such as MP4, MKV, MOV, or WebM.
MP4 is a container format, not a codec. An MP4 file usually contains compressed video such as H.264 or H.265 and audio such as AAC.
MKV is a container format. It can hold video, audio, subtitles, chapters, and metadata, but the video inside might use codecs such as H.264, H.265, AV1, or VP9.
WAV is a file format or container for audio. It usually contains uncompressed PCM audio, but WAV itself is not the same thing as the audio data inside.
Dolby Atmos is best understood as an immersive audio format and playback standard. It may be carried using codecs such as Dolby Digital Plus or Dolby TrueHD.
They often appear together in the same file or device label. A single movie file may use a container, one video codec, one audio codec, metadata, subtitles, and playback standards at the same time.
Yes. Two MP4 files can use different video and audio codecs. One MP4 might contain H.264 video and AAC audio, while another might contain H.265 video and Dolby Digital Plus audio.
Check the container, the video codec, the audio codec, subtitles, and the device or app's supported standards. The file extension alone does not always explain why playback fails.