Moving Picture Experts Group (MPEG) - MPEG-1

Moving Picture Experts Group, or known as MPEG for short, is a group of experts which design standards for video/audio transmition formed IEC and ISO. MPEG have many standards but we are just going to look at the few that are used or have been used within the industry.


MPEG-1


Layer 1


This layer contains the system information. the system information carries the video, audio, sync and other non video/audio data signals. the information keeps all of this information in time with each other as it has been multiplexed. the multiplexed encoded signal gets transmitted at 1.5Mbs. MPEG started the multiplexed digital signal. this signal is based on an on time, error free delivery of a stream of bytes. this code maintains the constant delay which embeds a clock in the byte stream that can be used by the receiver to control a clock reference in the receiver.



Layer 2



this layer contains the video data information. the layer has a few guidelines being,

- The video must be replayable forwards and backwards

- Fast forward/reverse modes have to be supported.

- Editing must be possible, such as replacing frames etc.



Layer 3



The audio layer also known as MP3 one of the popular choices in music formats as storage on PC systems and transmittion over the internet. It has made its way through one of the top music formats through PC . THis operates at bit rates in the range of 32 to 448 kb/s and supporting sampling frequencies of 32, 44.1 and 48 kHz. Usually for Layer II the bit rate ranges between 128-256 kbit/s, and 384 kb/s for professional applications. this layer has the abillity to carry 1 or 2 channel of audio content. Labelled layer I designed for low complexity decoding and encoding, and layer II designed for slightly higher complexity. Layer I can compress high quality audio data at bit rate of 384 kb/s while still able to recover high quality through to the decoding process.

Layer II has low complexity decoding combined with high robustness against cascaded encoding/decoding and transmission errors. This is ideal for digital video/audio broadcast applications (DVB and DAB).

So if the sampling frequency is 32 kHz then the input signal is transformed into 32 sub bands.giving layer II 36 subband samples totalling 1152 subband samples and Layer I with 12 subands totalling 384 subband samples over the sampling frequency.

More to come, Next will be MPEG-2