Set-Top Box Decoder Buffer for Fast Channel Switching

Solution Overview

Problem

In broadband communications systems, the MPEG buffer in set-top boxes must fully fill before decoding and displaying images, which can take up to two seconds, leading to delayed channel changes and potential underflow if playback begins prematurely.

Innovation Solution

Implementing a decoder buffer that initially outputs data at a lower rate than the natural stream rate when partially filled, allowing faster channel changes by filling the buffer while displaying images, and then increasing the output rate once the buffer is full.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the MPEG buffer is required to fully fill before decoding and displaying images, then buffer underflow is prevented, but channel change time increases to up to two seconds

Engineering Contradiction:

Improvebuffer underflow preventionVSAvoidchannel change time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by pre-fetching and storing data in the MPEG buffer before it is strictly needed for decoding. The buffer is proactively filled during periods when the decoder can operate on previously buffered data, so that when channel changes occur, the buffer is already prepared to prevent underflow while enabling faster switching.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the buffer is filled completely before playback, then image decoding reliability is improved, but the time required for channel changes increases

Engineering Contradiction:

Improveimage decoding reliabilityVSAvoidchannel change time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by pre-fetching and storing data in the MPEG buffer before it is strictly needed for decoding. The buffer is proactively filled during periods when the decoder can operate on previously buffered data, so that when channel changes occur, the buffer is already prepared to prevent underflow while enabling faster switching.

Inventive Principle:

Principle #10Preliminary action

3Speed

If playback begins before the buffer is full, then channel change time is reduced, but buffer underflow occurs

Engineering Contradiction:

Improvechannel change speedVSAvoidbuffer underflow prevention

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The system continuously monitors buffer occupancy levels and dynamically adjusts the decoder's operation based on feedback from the buffer state. When the buffer approaches critical levels, the system adjusts data retrieval and decoding rates to maintain sufficient buffer levels, preventing underflow while optimizing channel change performance.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7873760B2Expedited digital signal decoding

Publication Date: 2011.01.18 INTERDIGITAL CE PATENT HOLDINGS SAS

AI summary

Expedited digital signal decoding. A multicast or unicast data stream is sent from a headend to a set-top box at a natural rate. A decoder buffer in the set-top box begins to fill. Once the buffer is partially full, a decoder begins to decode the data at a rate lower than the natural rate. Images are displayed to the user before the buffer is full, allowing for a faster channel change.