What are Video Error Correction & Concealment Techniques?

One inherent problem with any communications system is that information may be altered or lost during transmission due to channel noise. The effect of such information loss can be devastating for the transport of compressed video, because any damage to the compressed bit stream may lead to objectionable visual distortion at the decoder. Transmission errors can be roughly classified into two categories:

Random bit errors and Erasure errors.

Random bit errors are caused by the imperfections of physical channels, which result in bit inversion, bit insertion, and bit deletion. Erasure errors, on the other hand, can be caused by packet loss in packet networks, burst errors in storage media due to physical defects, or system failures for a short time.

To combat these errors, various techniques have been developed over the years. Few examples are forward error correction (FEC) and automatic retransmission request (ARQ) algorithms.

Transmission related Error Detection Techniques:

Forward error correction refers to those techniques in which the encoder plays the primary role. FEC intelligently monitors the video conference for packet loss and jitter. When it detects packet loss, FEC will start to send extra data packets to compensate for the packet loss. When packet loss is no longer present, FEC will stop sending extra data packets

Interactive error concealment technique uses encoder and decoder working in cooperation to minimize the impact of transmission errors, examples in this category includes ARQ.

After Error Detection Concealment Techniques

Once the errors are detected using above mentioned and many other error detection algorithms, it is important to conceal the detected error at the encoder or decoder end. Similar to error detection algorithms, multiple error concealment techniques are also used by most of the video solution providers. Few of the well-known and widely used techniques are Temporal Error Concealment & Forward Error Concealment.

All of these introduce some level of redundancy at the classification stage, with the intention to simplify the error recovery process at the decoder (ideally, to eliminate the need for this error recovery process by the decoder). What can vary from one technique to another is where and how that redundancy is introduced.

Source: Huawei

Huawei uses Super error concealment technology for ensuring audio and video quality.

Polycom LPR (Lost Packet Recovery) feature allow protecting the video call experience from the effects of packet loss — especially random / bursty packet loss. It is one of the error protection algorithm used today that uses forward error correction (FEC) to recover lost data. Polycom LPR protects all parts of the video call, including the audio, video, and content / H.239 channels, from packet loss.

Lifesize uses Adaptive Motion Control with Forward Error Correction technology to keep video and audio quality from being degraded. It allows their It allows their systems to adapt to changing network conditions, auto-negotiating in real time to overcome network congestion and deliver an optimal video conferencing experience. Avaya Scopia video solutions also use Forward Error Correction & Concealment mechanism.

Vidyo uses its own patented error resilience algorithms based on temporal scalability technique to detect such losses with the very first packet that it correctly receives.


Originally published at www.techpillar.com.