Systems and methods for implementing efficient cross-fading between compressed audio streams

Patent metadata

Field	Value
Publication number	US-11961538-B2
Application number	US-202117522595-A
Country	US
Kind code	B2
Filing date	Nov 9, 2021
Priority date	Nov 18, 2011
Publication date	Apr 16, 2024
Grant date	Apr 16, 2024

Abstract

Systems and methods are presented for efficient cross-fading of compressed domain information streams on a user/client device. Exemplary systems may provide cross-fade between AAC/Enhanced AAC Plus information streams, between MP3 information streams, or between information streams of unmatched formats. These systems are distinguished in that cross-fade is directly applied to compressed bitstreams so a single decode operation is performed on the resulting bitstream. Thus, a set of frames from each input stream associated with the time interval in which a cross fade is decoded, and combined and recoded with a cross fade or other effect now in the compressed bitstream. Once sent through the client device's decoder, the user hears the transitional effect. The only input data that is decoded and processed is that associated with the portion of each stream used the crossfade, blend or other interstitial, and thus the vast majority of input streams are left compressed.

First claim

What is claimed:

1. A method for implementing efficient cross-fading between compressed audio streams, comprising:
obtaining parameters for a cross-fade between N audio streams comprising compressed packets;
time aligning the packets from each stream that are involved in the cross-fade;
synthesizing composite compressed packets containing information derived from the N streams; and
presenting the composite compressed packets to an audio decoder during a cross-fade phase;
wherein each stream is encoded with EAAC Plus, and said time aligning the packets is performed by estimating the time instance for an (i+i) th frame in the stream as:
t ( i+ 1)=( i* 2048*number_of_raw_data_blocks_in_frame)/sampling_frequency.

2. The method of claim 1 , wherein N=2, and said presenting compressed packets to an audio decoder includes multiplexing each of the streams and the synthesized composite compressed packets according to a time index, as follows:
For t less than or equal to T1, Stream 1;
For t greater than T1 but less than or equal to T2, synthesized composite compressed packets;
For t greater than T2, Stream 2.

3. The method of claim 1 , wherein each stream is encoded with EAAC Plus, and said time aligning the packets is performed by estimating the time instance for an (i+l) th frame in the stream by keeping a cumulative estimate of the total number of raw data blocks till the i th frame as follows:

total_number
⁢
_of
⁢
_raw
⁢
_data
⁢
_blocks
⁢
_in
⁢

_frame
i

=

∑

k
=
1

k
=
i

number_of
⁢
_raw
⁢
_data
⁢
_blocks
⁢
_in
⁢

_frame
k

and estimating:

t
⁡
(

i
+
1

)

′

=

(

2048
*
total_number
⁢
_of
⁢
_raw
⁢
_data
⁢
_blocks
⁢
_in
⁢

_frame
i

)

sampling_frequency

4. The method of claim 1 , wherein said time aligning is performed by operating upon data in a frame header of the stream.

5. The method of claim 4 , wherein each stream is encoded with EAAC Plus, and said data includes one or more of: sampling_frequency index, frame_length, adts_buffer_fullness, and number_of_raw_data_blocks_in_frame.

6. The method of claim 1 , wherein said synthesizing composite compressed packets includes decomposing the data from each stream into its components, and separately combining each group of respective components.

7. The method of claim 6 , wherein N=2, and wherein each stream is encoded with EAAC Plus, and wherein packet pairs P(1,i) and P(2,j) can be both partially demultiplexed to identify three subcomponents, AAC Core, SBR, and PS, and wherein the respective subcomponents are combined to generate the composite subcomponents.

8. The method of claim 7 , wherein different combination strategies are used for the three subcomponents.

9. The method of claim 8 , wherein for the SBR and PS subcomponents an AB decision can be made favoring the dominating stream at any given instance, and wherein for the AAC Core subcomponent a more complex combination algorithm is employed.

10. The method of claim 6 , wherein the composite subcomponent packets are combined to produce a full composite bitstream packet.

11. A non-transitory computer readable medium containing instructions that, when executed by at least one processor of a computing device, cause the computing device to:
obtain parameters for a cross-fade between N audio streams comprising compressed packets;
time align the packets from each stream that are involved in the cross-fade;
synthesize composite compressed packets containing information derived from the N streams; and
present the composite compressed packets to an audio decoder during a cross-fade phase;
wherein each stream is encoded with EAAC Plus, and said time aligning the packets is performed by estimating the time instance for an (i+l) th frame in the stream as:
t ( i+ 1)=( i* 2048*number_of_raw_data_blocks_in_frame)/sampling_frequency.

12. The non-transitory computer readable medium of claim 11 , wherein N=2, and said presenting compressed packets to an audio decoder includes multiplexing each of the streams and the synthesized composite compressed packets according to a time index, as follows:
For t less than or equal to T1, Stream 1;
For t greater than T1 but less than or equal to T2, synthesized composite compressed packets;
For t greater than T2, Stream 2.

13. The non-transitory computer readable medium of claim 11 , wherein each stream is encoded with EAAC Plus, and said time aligning the packets is performed by estimating the time instance for an (i+l) th frame in the stream by keeping a cumulative estimate of the total number of raw data blocks till the i th frame as follows:

total_number
⁢
_of
⁢
_raw
⁢
_data
⁢
_blocks
⁢
_in
⁢

_frame
i

=

∑

k
=
1

k
=
i

number_of
⁢
_raw
⁢
_data
⁢
_blocks
⁢
_in
⁢

_frame
k

Assignees

• Sirius Xm Radio Inc

Inventors

• Lowe Raymond
• Kalman Mark
• Sinha Deepen
• Ward Christopher

Classifications

• G11B27/038 Primary

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