Glossary of File Conversion Terms: Codec, Container, Bitrate and More

Plain English definitions of the terms you meet when converting images, audio and video, from bitrate and sample rate to codec and container.

Core terms

Codec: software that encodes and decodes data, such as H.264 for video, AAC for audio and JPEG for images.

Container: the file format that holds one or more encoded streams, for example MP4, MOV, MKV or WebM.

Bitrate: data used per second, measured in kilobits per second (kbps) for audio and megabits per second (Mbps) for video.

Sample rate: how many audio samples are taken each second, for example 44.1 kHz for CD audio and 48 kHz for video.

Bit depth: the number of bits per sample or per colour channel. CD audio uses 16 bits and a standard JPG uses 8 bits per channel.

Resolution: the pixel dimensions of an image, such as 4032 by 3024.

Alpha channel: the part of an image that stores transparency.

Metadata (EXIF): information such as camera model, date and location stored inside a photo.

Artefact: visible distortion, such as blockiness, caused by heavy lossy compression.

Frame rate: how many video frames are shown per second, commonly 24, 30 or 60.

Variable bitrate (VBR): encoding that uses more data for complex passages and less for simple ones.

Transcoding: converting from one codec or format to another, which for lossy formats re-compresses the data.

Remuxing: changing only the container without re-encoding, which is fast and lossless.

PDF: Portable Document Format, standardised as ISO 32000.

Rasterising: turning vector or text content into a pixel image, as when a PDF page becomes a JPG.

Embedding: storing fonts or images inside a file so it displays the same everywhere.

WebAssembly: a binary format that lets browsers run compiled code, used to convert files locally.

FFmpeg: an open source toolkit for converting audio and video.

HEIC / HEIF: Apple's default photo format and the standard it is based on.

What is the difference between a codec and a container?

The codec compresses the audio or video, and the container is the file wrapper that stores the compressed streams together.

What does transcoding mean?

It means decoding a file and encoding it again in a different format or setting.

Last updated 9 October 2026. Written by ARTH, a design and build studio in Coimbatore.