A codec is the method, in software or in a hardware chip, that compresses video or audio into a smaller stream and decompresses it again for playback; the word is short for coder-decoder. It is not the same thing as the file type. An .mp4 or .mov file is a container, and the codec is what sits inside it: H.264 video in an MP4 file is the most common pairing on the web.
What is a codec?
Every codec has two halves. The encoder turns raw frames or audio samples into a compact bitstream, and the decoder turns that bitstream back into pictures or sound. The two must agree exactly, which is why codecs are defined by published standards: a file encoded on one camera can be decoded by any player that implements the same specification.
Raw video is enormous. One second of uncompressed 1920 × 1080 video at 30 frames per second in 8-bit RGB is 1920 × 1080 × 3 bytes × 30, about 187 MB, or roughly 1.5 gigabits. A codec's job is to cut that by a factor of a hundred or more while keeping the picture looking the same to a viewer.
Lossy and lossless
Most video codecs are lossy: the decoded picture is close to the original but not identical, and MDN's web video codec guide notes that the loss depends on the compression settings. Lossless codecs rebuild every pixel exactly and make much larger files, so they suit editing and archiving rather than delivery.
How a video codec saves space
The big saving comes from time, not from single images. Consecutive frames are usually similar, so a video codec stores a full keyframe now and then and, for the frames in between, records how blocks of the picture moved and what changed. MDN calls this motion compensation. A mostly still scene costs very little after its first frame.
The amount of data the encoder may spend per second is the bitrate, and it sets the balance between size and quality. For recommended numbers by resolution and frame rate, use the video bitrate calculator; this page stays on the codecs themselves.
Codec vs container: H.264 in MP4, MOV and WebM
A container is a file format that wraps one or more compressed streams together with timing and metadata, according to MDN's media container guide. The codec is the compression inside each stream. A file's extension tells you the container, not the codec, so two files that both end in .mp4 can need different decoders.
| Container | Common video codecs | Common audio codecs | Where it plays |
|---|---|---|---|
| MP4 (.mp4) | H.264, HEVC, AV1, VP9 | AAC, Opus, MP3, FLAC | Every major browser and phone when the video is H.264; HEVC and AV1 depend on the device |
| QuickTime (.mov) | H.264, HEVC, Apple ProRes | AAC, Apple Lossless | Apple devices natively; elsewhere only when the codec inside is supported |
| WebM (.webm) | VP8, VP9, AV1 | Opus, Vorbis | All major browsers; less common in desktop editors |
| Matroska (.mkv) | Almost any | Almost any | Desktop players such as VLC; inconsistent in browsers |
The table shows common pairings, not every legal one. The practical consequence is the familiar "this file won't play" error: a .mov from an iPhone set to High Efficiency holds HEVC video, and a browser or editor without an HEVC decoder rejects it even though it opens other .mov files. The video to GIF converter covers the fix when that happens in a browser tool.
How to tell which codec a file uses
On a Mac, select the file in Finder and choose Get Info; the More Info section lists its codecs, such as
H.264 and AAC. In VLC on any system, open the file and check the codec information window. From a
terminal, ffprobe -v error -show_entries stream=codec_name -of csv=p=0 clip.mp4 prints one
codec name per stream, for example h264 and then aac.
The video codecs you will actually meet
Four video codecs cover nearly everything you will record, download or upload today. Two come from the ITU-T and ISO/IEC standards bodies and carry patent licensing; two are open and royalty-free, according to MDN's codec guide.
H.264 / AVC
H.264, also called Advanced Video Coding, is ITU-T Recommendation H.264, "Advanced video coding for generic audiovisual services", currently in its June 2026 edition. Every major browser, phone and editor decodes it, which makes it the safe default. MDN notes that commercial use needs a patent licence, though the Via LA pool waives fees for free internet video.
H.265 / HEVC
HEVC, High Efficiency Video Coding, is ITU-T Recommendation H.265, with a current edition dated January 2026. MDN says it can in theory reach half the file size of H.264 at comparable quality. Browser support arrived late and still leans on hardware: MDN lists Chrome 107 and later, Safari on macOS High Sierra and later, and Firefox from version 134 on Windows.
HEVC is also the answer to "what codec does iPhone use". Apple's article on HEIF and HEVC media on Apple devices says iPhone 7 and later, on iOS 11 or later, record HEVC when Settings > Camera > Formats is set to High Efficiency, and H.264 when it is set to Most Compatible. When you share with a device that cannot play HEVC, iOS may send a more compatible H.264 copy instead.
VP9
VP9 is Google's open, royalty-free codec, published through the WebM Project, which dates its availability to 17 June 2013. MDN puts its quality in the same class as HEVC. It plays in all major browsers, though Safari does not support VP9 video with an alpha channel, and it usually travels in a WebM file alongside Opus audio.
AV1
AV1 is the open, royalty-free codec from the Alliance for Open Media. MDN credits it with compression about 50% better than H.264. It plays in every major browser, but Safari support is limited to devices with AV1 hardware, which MDN lists as M3-generation Macs, the iPhone 15 Pro and iPhone 16 models onward. A fallback H.264 file is still wise.
What "multi format codec" means on a spec sheet
Intel's processor specification pages have a graphics row called Multi-Format Codec Engines, usually showing 1 or 2. It counts fixed-function media blocks: circuits in the integrated GPU that encode and decode video without using the CPU cores. Intel sells this capability as Quick Sync Video.
Intel's oneAPI GPU Optimization Guide, in its "Media Engine Hardware" chapter, describes the multi-format codec (MFX) block as "hardware decode and encode" and says the media engine "runs completely independent of compute engines". Because the block is fixed-function, it is fast and draws little power.
What more engines buy you
A second engine gives the chip a second block for video work. That helps when several streams run at once, such as a multicam edit or a batch transcode. A single export does not necessarily finish twice as fast, because the software decides how the work is split.
What it does not mean
The number is not a count of supported codecs, and it has nothing to do with software codec packs. Supported codecs are listed separately by processor generation; the tables in the same Intel guide cover H.264, HEVC, VP9, AV1 and MPEG-2. "Multi-format" means one engine handles several of them.
Hardware vs software encoding
Hardware encoders are fixed-function blocks like the one above: Intel Quick Sync, the media engines in Apple silicon (reached through Apple's VideoToolbox framework) and NVIDIA NVENC. They are fast and power-efficient. Software encoders such as x264 run on the CPU and can search longer for the smallest file at a given quality, at the cost of speed.
Browsers expose the same choice. The
W3C WebCodecs specification
lets a web page ask for "prefer-hardware", "prefer-software" or "no-preference" when it configures an
encoder or decoder, and check support first with isConfigSupported(). Support varies by device,
which is why an HEVC .mov may convert in a browser tool on one computer and fail on another.
Which codec to choose for an upload or export
Choose for the weakest player in your audience. For almost every upload that means H.264 video and AAC audio in an MP4 file, MDN's broad-compatibility option. YouTube and most social platforms re-encode what you send, so a more efficient codec in the upload rarely makes the viewer's copy smaller. To shrink a phone clip before sending it, the video compressor re-encodes it on your device.
| Job | Container and codec | Why |
|---|---|---|
| Social upload, YouTube, messaging | MP4 · H.264 + AAC | Decoded everywhere, and the pairing YouTube recommends |
| Smaller files on Apple devices | MOV or MP4 · HEVC | Up to about half the size of H.264 at similar quality, per MDN; native on Apple hardware |
| Video on your own website | WebM · AV1 (or VP9), plus an MP4 · H.264 fallback | The pair MDN recommends for the open web |
| Editing master or archive | MOV · Apple ProRes, or a lossless codec | Each frame stands alone, so editing is smooth; files are very large |
| Short silent loop for chat or docs | GIF, animated WebP or MP4 | Depends on where it must autoplay; see the GIF vs WebP vs APNG vs MP4 comparison |
For the pixel size and bitrate to pair with the codec, the YouTube video size sheet lists YouTube's recommended upload settings, and the 2.5K and 4K resolution guide covers what higher resolutions cost in file size.
If the video will be generated rather than filmed, Playcut's app accepts MP4, WebM and QuickTime (.mov) uploads and treats a GIF as an image. The AI video generator page lists the models Playcut runs and the aspect ratios each renders.