.MP2

Introduction

MP2 is Layer II of the MPEG-1 audio standard (ISO/IEC 11172-3), the older and simpler sibling of MP3. It needs a higher bit rate than MP3 for the same quality, but it is robust and cheap to decode, so broadcasters adopted it: it is the audio of DAB digital radio, of DVB television and of Video CD, and is still used in broadcast studios.

Structure

An MP2 file is a run of independent frames, laid out like MP3. Each frame starts with a 4-byte header: an 11-bit sync word of ones, then the MPEG version, the layer (Layer II), a protection flag, the bit rate, the sample rate, a padding flag and the channel mode. An optional CRC follows, then the bit allocation, scale factors and quantised samples. A Layer II frame holds 1152 samples per channel. Files may also carry ID3 tags.

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