HDMI ARC Latency Estimation for Lipsync
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Solution Overview
Problem
In videoconferencing setups where a TV is used as a monitor with separate speakers, achieving perfect lipsync is challenging due to unknown video latency, as most consumer televisions do not reliably report this latency through EDID or CEC information, leading to significant and annoying sync failures.
Innovation Solution
The system uses the HDMI audio return channel to estimate video latency by sending a maximum length sequence signal and applying a Hadamard Transformation to the received signal to identify the impulse response, allowing for accurate delay calculation and synchronization of audio and video.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the system uses EDID or CEC information to obtain video latency, then the implementation is simple, but the reliability is poor because most consumer televisions do not report the video latency
Solution Approach 1:
The patent uses the HDMI audio return channel as an intermediary to measure video latency. Instead of relying on the TV to report latency through EDID or CEC, the system sends an audio signal through the HDMI cable's return channel and measures the delay introduced by the TV's video processing. This intermediary measurement approach bypasses the unreliable reporting mechanism while still obtaining the needed latency information.
2Device complexity
If the system does not compensate for video latency, then the system complexity is low, but the audio-video synchronization quality deteriorates significantly
Solution Approach 1:
The patent implements a feedback mechanism where the system measures the video latency introduced by the TV through the HDMI audio return channel, then uses this measured latency information to adjust the audio playback timing. The measurement process sends a test signal, receives the delayed signal back through ARC, measures the delay, and feeds this information back to the audio processing system to compensate for the latency, achieving synchronized audio-video output.
3Measurement precision
If the system uses the HDMI audio return channel to measure latency, then the measurement accuracy is high, but the device complexity increases due to additional signaling requirements
Solution Approach 1:
The patent leverages the existing HDMI audio return channel, which is already part of the standard HDMI interface, to perform latency measurement. The ARC channel was originally designed for audio transmission, but the patent makes it serve a dual purpose: normal audio transmission and latency measurement. By using the existing infrastructure rather than adding separate measurement hardware or protocols, the patent achieves accurate measurements without significantly increasing device complexity.
Data Source
AI summary
Disclosed is a method that includes receiving an audio video stream, decoding the audio video stream to yield decoded video and decoded audio, transmitting the decoded video on a video cable to a display, transmitting a signal, such as, for example, a signal on an audio channel of the video cable, identifying an impulse response based on a received signal responsive to the transmitting of the signal, identifying a delay amount based on the impulse response and transmitting the decoded audio to a loudspeaker according to the delay amount. The cable can include an HDMI cable with the audio return channel (ARC) capability.