Mp4a.40.2 -140- ((better)) Jun 2026

Thus, the string mp4a.40.2 -140- literally reads as: "MPEG-4 AAC-LC audio, presented in the format profile #140."

It is highly probable that "-140-" is a transcription error derived from visual confusion.

At first glance, it looks like a random serial number. However, this string is a precise, technical handshake between a media server and a player. It dictates exactly how audio should be decoded, packaged, and played back. mp4a.40.2 -140-

audio profile, which is the most widely used audio codec for digital video and streaming today. Technical Context Definition : It is a part of the MPEG-4 standard (Object Type 2). : You will commonly see this string in HLS (HTTP Live Streaming) manifests and AWS Elemental MediaTailor

One of the reasons for the dominance of mp4a.40.2 is its "Low Complexity" nature. Unlike more advanced codecs that require significant processing power, AAC-LC was designed to be decoded easily by everything from high-end workstations to low-power smartphones and early iPods. This versatility ensured that as the world transitioned from physical media to digital streaming, there was a unified language for sound that worked across all ecosystems—Android, iOS, Windows, and macOS alike. The Bridge to the Future Thus, the string mp4a

This is an descriptor defined in ISO/IEC 14496-3 (MPEG-4 Audio).

The identifier refers to the AAC-LC (Advanced Audio Coding - Low Complexity) It dictates exactly how audio should be decoded,

The technical identifier refers to a specific audio stream configuration commonly used in digital streaming. It represents a high-quality, widely compatible AAC audio codec typically delivered via DASH (Dynamic Adaptive Streaming over HTTP). Technical Breakdown of the Codec