Synchronisation of audio and video signals
First Claim
1. A method of adaptively time-shifting an encoded audio signal relative to an encoded video signal in a received audio/video message stream such that a corresponding decoded audio signal and a corresponding decoded video signal are aligned in time within a maximum degree of deviation (Δ
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max),the encoded audio signal being divided into audio frames (Fa) having a first frame interval (Ta),the encoded video signal being divided into video frames (Fv) having a second frame interval (Tv),determining a desired delay (Dd) of the encoded audio signal for the corresponding decoded audio and video signals to be aligned in time within the maximum degree of deviation (Δ
max), the method characterised by the steps of;
calculating a frame delay number (nD) as one of the two neighbouring integers to a ratio between the desired delay (Dd) and the first frame interval (Ta),storing sequentially a number of audio frames (Fa(1)-Fa(5)) equal to the frame delay number (nD) before decoding a matching video frame (Fv(1)),decoding the matching video frame (Fv(1)),decoding the stored audio frames (Fa(1)-Fa(5)) in the sequential order of storage, andrepeating the above steps for remaining audio frames ((Fa(6)-Fa(k)) respective video frames (Fv(2)-Fv(m)) of the audio/video message stream.
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Abstract
The present invention relates to adaptive time-shifting of audio frames (Fa) in encoded audio signal relative to video frames (Fv) in encoded video signal, which together form an audio/video message steam such that the corresponding decoded audio and video signals are aligned in time within the maximum degree of deviation. The invention accomplishes this alignment by determining a desired delay of the encoded audio signal for the decoded signals to meet deviation requirement The desired (Dd) delay is then converted into a frame delay number (nD), which is calculated as one of the two neighbouring integers to a ratio between the desired delay (Dd) and an interval (Ta) at which the audio frames (Fa) are received. A number of audio frames (Fa) equal to the frame delay number (nD) are alternately stored into respective read out from FIFO-buffers (309; 310) such that sufficiently delayed audio frames (Fa) are delivered to an audio decoding unit (313). After signal decoding (313; 315) synchronized audio and video information can thus be presented via a loudspeaker (314) and a video monitor (316) respectively.
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Citations
15 Claims
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1. A method of adaptively time-shifting an encoded audio signal relative to an encoded video signal in a received audio/video message stream such that a corresponding decoded audio signal and a corresponding decoded video signal are aligned in time within a maximum degree of deviation (Δ
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max),
the encoded audio signal being divided into audio frames (Fa) having a first frame interval (Ta), the encoded video signal being divided into video frames (Fv) having a second frame interval (Tv), determining a desired delay (Dd) of the encoded audio signal for the corresponding decoded audio and video signals to be aligned in time within the maximum degree of deviation (Δ
max), the method characterised by the steps of;calculating a frame delay number (nD) as one of the two neighbouring integers to a ratio between the desired delay (Dd) and the first frame interval (Ta), storing sequentially a number of audio frames (Fa(1)-Fa(5)) equal to the frame delay number (nD) before decoding a matching video frame (Fv(1)), decoding the matching video frame (Fv(1)), decoding the stored audio frames (Fa(1)-Fa(5)) in the sequential order of storage, and repeating the above steps for remaining audio frames ((Fa(6)-Fa(k)) respective video frames (Fv(2)-Fv(m)) of the audio/video message stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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max),
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9. An apparatus for adaptively time-shifting an encoded audio signal relative to an encoded video signal in a received audio/video message stream such that a corresponding decoded audio signal respective decoded video signal are aligned in time within a maximum degree of deviation, the encoded audio signal being divided into audio frames (Fa) having a first frame interval (Ta), the encoded video signal being divided into video frames (Fv) having a second frame interval (Tv), the apparatus characterised in that it comprises
a first buffer (309) sequentially storing received audio frames (Fa), a second buffer (310) sequentially storing received audio frames (Fa), and a controller (312) storing a first frame interval value (Ta) representing a time span between two consecutively generated audio frames (Ta), deriving and storing a desired delay value (Dd) from timing indications (tsa, tsv) of the received audio frames (Fa) and the received video frames (Fv) in the received audio/video message stream, the desired delay value (Dd) indicating a necessary delay of the audio frames (Fa) for the decoded audio and video signals to be aligned in time within the maximum degree of deviation, calculating a frame delay number (nD) as one of the two neighbouring integers to a ratio between the desired delay value (Dd) and the first frame interval value (Ta), and controlling an alternate storage of delay number (nD) audio frames (Fa) into the first buffer (309) during read-out of delay number (nD) audio frames (Fa) from the second buffer (309) respective storage of delay number (nD) audio frames (Fa) into the second buffer (310) during read-out of delay number (nD) audio frames (Fa) from the first buffer (309).
Specification