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Glossary

H.264

Also known as: AVC, Advanced Video Coding, MPEG-4 AVC

H.264 was finalized in 2003 and has dominated web video ever since. It uses a combination of motion prediction (only storing the differences between similar frames), spatial transforms, and entropy coding to achieve compression ratios around 50:1 — meaning a 1-hour 1080p video that would be 670GB uncompressed compresses down to roughly 13GB or less depending on quality settings.

The reason H.264 dominates over newer codecs (H.265 / HEVC, AV1, VP9) is hardware support. Every iPhone, Android device, smart TV, web browser, and gaming console has H.264 decoding built into the GPU, so playback is essentially free in terms of battery and CPU. Newer codecs offer better compression but require either software decoding (slower, drains battery) or newer hardware that not all users have.

When you download a video from a social platform, the file is almost always H.264 video inside an MP4 container with AAC audio. This combination is the de-facto standard for shareable web video and plays on every device you'd ever want to play it on.

Related terms

MP4
MP4 (MPEG-4 Part 14) is a digital container format that holds video, audio, subtitles, and metadata in a single file. It is the dominant video format on the modern internet — TikTok, Instagram, YouTube, X / Twitter, Facebook, and Reddit all serve videos as MP4 internally.
AAC Audio
AAC (Advanced Audio Coding) is a lossy audio compression codec designed as the successor to MP3. It is the audio format inside almost every MP4 video file served by TikTok, Instagram, YouTube, Facebook, and Twitter, and at the same bitrate it sounds noticeably better than MP3.
Bitrate
Bitrate is the amount of data used to encode each second of video, measured in kilobits per second (kbps) or megabits per second (Mbps). Higher bitrate means more data per second, which means better visual quality but larger file size. At the same resolution, a higher-bitrate video looks substantially better than a lower-bitrate one.
1080p
1080p is a video resolution of 1920×1080 pixels (1920 wide by 1080 tall) — also called Full HD. The 'p' stands for progressive scan, meaning every frame is rendered as a complete image rather than interlaced. 1080p is the maximum resolution at which TikTok, Instagram, Twitter / X, and Facebook serve video.