Creator media glossary
What is a codec?
Short answer
The algorithm that compresses video or audio data - H.264 and AAC are the two you'll run into most, packed inside a container like MP4.
Key takeaways
- A codec compresses video or audio for storage and decompresses it for playback; the container (MP4, MOV) is the box it travels in.
- H.264 video with AAC audio is the safe choice for uploads; HEVC and AV1 make smaller files but play on fewer devices.
- Editing codecs such as ProRes trade huge files for smooth editing; delivery codecs do the opposite.
- Every lossy encode loses a little quality, so encode once from the best source.
Codec explained
A codec is not the same thing as a file format: MP4 and MOV are containers, while H.264, HEVC, VP9 and AV1 are the codecs that actually compress the picture inside them. The same container can hold different codecs, which is part of why two .mp4 files can behave completely differently on upload.
The codec is what determines hardware decoding support (does this phone's chip know how to play it instantly), compression efficiency (how small a file gets at a given quality) and editing compatibility - H.264 is decoded natively on essentially everything; newer codecs trade some of that universality for smaller files.
How a codec compresses video
Raw video is enormous: one minute of uncompressed 1080p at 30 fps with 8-bit 4:2:0 color is about 5.6 GB. A codec gets that down to tens of megabytes by removing information that is repeated or that viewers will not miss. Every modern video codec, from H.264 to AV1, uses the same four steps.
1. Prediction
Each frame is cut into blocks. A block is predicted either from neighboring pixels in the same frame (intra prediction) or from a matching area in an earlier or later frame, found by motion search (inter prediction). Only the difference between the prediction and the real picture, the residual, is kept.
2. Transform
The residual is converted into frequencies with a transform related to the DCT. Most of the visual energy collects in a few low-frequency values, which is what makes the next step effective.
3. Quantisation
The frequency values are rounded to coarser steps, and fine detail that the eye barely sees is dropped. This is the only step that loses information, and the bitrate or quality setting controls how hard it rounds.
4. Entropy coding
The rounded values and motion vectors are packed with lossless coding (CABAC in H.264 and HEVC) so the most common patterns take the fewest bits. The decoder runs the same steps in reverse.
Types of codecs
Lossy and lossless
Lossy codecs (H.264, HEVC, AV1, AAC, MP3) discard detail to make small files and are what platforms deliver. Lossless codecs (FLAC, PNG, FFV1) restore every bit and are used for archiving and editing.
Delivery and editing codecs
Delivery codecs squeeze hard and make every frame depend on others, which is ideal for streaming and uploads. Editing (intermediate) codecs such as Apple ProRes and Avid DNxHR compress each frame on its own, so editors can scrub and cut smoothly at the cost of much larger files.
Software and hardware codecs
A software codec runs on the CPU and is flexible; a hardware codec is a dedicated block in a GPU or phone chip (NVIDIA NVENC, Intel Quick Sync, Apple VideoToolbox) that encodes or decodes far faster and with less battery. Whether a device plays HEVC or AV1 smoothly usually depends on hardware support.
A short history of video and audio codecs
| Year | Codec | What it made possible |
|---|---|---|
| 1988 | H.261 | Video calls over ISDN lines; the first practical digital video standard |
| 1993 | MPEG-1 (and MP3 audio) | Video CD and, through its Layer III audio, the MP3 file |
| 1995 | MPEG-2 | DVD and digital TV broadcasting |
| 1997 | AAC | Better audio than MP3 at the same bitrate; later the audio of MP4 and iTunes |
| 1999 | MPEG-4 Part 2 | DivX and Xvid files shared over the early internet |
| 2003 | H.264 (AVC) | HD streaming, Blu-ray and phone video; still the most compatible codec |
| 2012 | Opus | Open, low-latency audio for calls and the web |
| 2013 | HEVC (H.265) and VP9 | Practical 4K and HDR; about half the bitrate of H.264 |
| 2018 | AV1 | Royalty-free compression beyond HEVC, now used by YouTube and Netflix |
| 2020 | H.266 (VVC) | The next ITU standard, aimed at 8K and 360° video |
Common codecs and the containers that carry them
| Codec | Kind | Usual containers | Notes |
|---|---|---|---|
| H.264 (AVC) | Video | MP4, MOV, MKV | Plays almost everywhere; the upload default |
| H.265 (HEVC) | Video | MP4, MOV | Smaller files than H.264; narrower playback support |
| VP9 | Video | WebM | Open and royalty-free |
| AV1 | Video | MP4, WebM | Open and royalty-free; most efficient, newest |
| ProRes | Video | MOV | Editing and mastering; very large files |
| AAC | Audio | MP4, MOV | The upload default for audio |
| Opus | Audio | WebM, MP4 | Open; YouTube accepts it for uploads |
| MP3 | Audio | MP3, MP4 | Universal audio-only format |
Audio codecs compared
| Codec | Type | Typical use | Notes |
|---|---|---|---|
| AAC | Lossy | Audio in MP4 video, Apple Music, YouTube | The upload default |
| MP3 | Lossy | Podcasts, music downloads | Universal; patents expired in 2017 |
| Opus | Lossy | WebM video, calls, WhatsApp and Discord voice | Best quality per bit; royalty-free |
| FLAC | Lossless | Music archives, hi-res downloads | About half the size of WAV |
| PCM (WAV, AIFF) | Uncompressed | Recording, editing, masters | Very large; often rejected by social uploads inside video |
| AC-3 and E-AC-3 (Dolby Digital) | Lossy | Blu-ray, broadcast, streaming surround | Not documented by social platforms |
Which codec to use
| Job | Video codec | Audio codec |
|---|---|---|
| Posting to social platforms | H.264 (HEVC where documented) | AAC |
| Sending a file anyone can open | H.264 in MP4 | AAC |
| Editing and color grading | ProRes or DNxHR | PCM |
| Archiving a finished master | ProRes, or HEVC or AV1 at high quality | PCM or FLAC |
| Video on your own website | AV1 or VP9 with an H.264 fallback | Opus or AAC |
| Live streaming | H.264 (AV1 or HEVC where the platform supports it) | AAC |
How to find out which codec a file uses
On any computer, the free MediaInfo app or VLC (Tools > Codec Information, on a Mac Window > Media Information) shows the codec of every stream. Our file checker does the same in the browser without uploading the file.
Look at the video and the audio stream separately: a file can have H.264 video and Opus audio, and a platform may accept one and not the other.
Free tools:File inspectorCheck a file against platform limits
"Missing codec" errors and codec packs
When a player says a codec is missing, it means the file is fine but the player cannot decode its streams. The usual fixes, in order:
- Play it in VLC, which carries its own decoders for almost every format.
- On Windows, install the codec from Microsoft: HEVC Video Extensions for iPhone and drone footage, AV1 Video Extension for AV1.
- Convert the file to H.264 and AAC in MP4, which every player decodes.
- Avoid all-in-one "codec packs": Microsoft discourages installing them, recommends removing them if the player misbehaves, and says to install codecs only from trusted sources such as the provider's own site. Fake codec downloads are also an old way of spreading malware.
Frequently asked questions
What is a codec?
A codec (coder-decoder) is the method used to compress video or audio for storage and decompress it for playback. H.264, HEVC, VP9 and AV1 are video codecs; AAC, Opus and MP3 are audio codecs.
Codec vs container: what is the difference?
The codec compresses each stream; the container (MP4, MOV, WebM, MKV) is the file that packages the video stream, audio stream and metadata together. The file extension names the container, not the codec.
Which codec should I use for social media?
H.264 video with AAC audio in an MP4: YouTube's recommended upload settings use H.264, and every major platform in our registry documents H.264.
How do I find out which codec a video uses?
Open the file in a media inspector (or our free file checker): it reads the container and reports the video and audio codecs without uploading the file.
What does codec stand for?
Coder-decoder (sometimes compressor-decompressor). The encoder side compresses media for storage or streaming; the decoder side restores it for playback.
Is MP4 a codec?
No, MP4 is a container. It holds streams compressed by codecs, usually H.264 or HEVC video and AAC audio. The same applies to MOV, MKV and WebM.
Which video codec is best?
For uploads and sharing, H.264 because everything plays it. For smaller files at the same quality, HEVC or AV1, if the devices and platforms you target support them. For editing, an intermediate codec such as ProRes.
Let Koldflux pick the settings
Koldflux chooses the codec, container and bitrate for each platform when it exports.
Free tools that use this
Sources and how we checked
- MDN: Web video codec guide (checked 2026-10-05)
- MDN: Media container formats (checked 2026-10-05)
- YouTube Help: Recommended upload encoding settings (checked 2026-10-05)
- ITU-T Recommendation H.264: Advanced video coding for generic audiovisual services (checked 2026-10-06)
- ITU-T Recommendation H.265: High efficiency video coding (checked 2026-10-06)
- Microsoft Store: HEVC Video Extensions (checked 2026-10-06)
- Microsoft Support: Codecs FAQ (checked 2026-10-06)
Reviewed October 6, 2026 by the Koldflux team. Definitions follow the specifications and platform documentation linked above; platform tables come from the same registry the Koldflux tools use.