TRANSCODER USING ENCODER GENERATED SIDE INFORMATION

• US 20090125315A1
• Filed: 11/09/2007
• Published: 05/14/2009
• Est. Priority Date: 11/09/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Chen, Wei-Ge, Koishida, Kazuhito, Mehrotra, Sanjeev
• Granted Patent: US 8,457,958 B2
• Time in Patent Office: Days
• US Class Current: 704/503
• CPC Class Codes: G10L 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding

Abstract

An audio encoder encodes side information into a compressed audio bitstream containing encoding parameters used by the encoder for one or more encoding techniques, such as a noise-mask-ratio curve used for rate control. A transcoder uses the encoder generated side information to transcode the audio from the original compressed bitstream having an initial bit-rate into a second bitstream having a new bit-rate. Because the side information is derived from the original audio, the transcoder is able to better maintain audio quality of the transcoding. The side information also allows the transcoder to re-encode from an intermediate decoding/encoding stage for faster and lower complexity transcoding.

Claims

1. A method of transcoding an audio bitstream from an initially coded bit-rate to a target bit-rate, the method comprising:

receiving the audio bitstream from an audio encoder, the audio bitstream containing encoding parameters generated by the encoder for one or more encoding techniques employed by the encoder for encoding the audio bitstream from an audio input;

decoding the encoding parameters from the audio bitstream;

partially decoding audio content of the audio bitstream to an intermediate decoding stage prior to an inverse frequency transform;

adjusting the encoding parameters for the target bit-rate;

encoding the decoded audio content based on the encoding parameters adjusted for the target bit-rate; and

producing an output bitstream containing the encoded audio content.

2. The method of claim 1 wherein said encoding parameters comprise parameters for a multi-channel transform.

3. The method of claim 1 wherein said encoding parameters comprise parameters for bark weighting.

4. The method of claim 1 wherein said encoding parameters comprise parameters for frequency extension coding.

5. The method of claim 1 wherein said encoding parameters comprise rate control parameters.

6. The method of claim 5 wherein said encoding parameters comprise data characterizing a quality to quantization step size curve.

7. The method of claim 6 wherein said encoding parameters comprise data characterizing a noise mask ratio versus quantization step size curve.

8. The method of claim 6 wherein said encoding parameters comprise a plurality of anchor points on a noise mask ratio versus quantization step size curve.

9. A transcoder comprising:

an input for receiving an input audio bitstream encoded at an initial bit-rate by an audio encoder, the compressed audio bitstream containing encoding parameters generated by the encoder for one or more encoding techniques employed by the encoder during encoding the compressed audio bitstream from an audio input;

a partial audio decoder having a plurality of decoding modules and operating to decode audio content of the compressed audio bitstream to an intermediate decoding state;

a side information decoder for decoding the encoding parameters from the compressed audio bitstream;

a partial audio encoder having a plurality of encoding modules and operating to re-encode the audio content from the intermediate decoding state for a target bit-rate based on the encoding parameters; and

an output for producing an output audio bitstream containing the re-encoded audio content having the target bit-rate.

10. The transcoder of claim 9 wherein said encoding parameters comprise parameters for a multi-channel transform.

11. The transcoder of claim 9 wherein said encoding parameters comprise parameters for bark weighting.

12. The transcoder of claim 9 wherein said encoding parameters comprise rate control parameters.

13. The transcoder of claim 12 wherein said encoding parameters comprise data characterizing a quality to quantization step size curve.

14. The transcoder of claim 12 wherein said encoding parameters comprise a plurality of anchor points on the quality to quantization step size curve.

15. The transcoder of claim 9 wherein said audio content in said intermediate decoding state is in the form of frequency transform coefficients and said partial audio decoder omits an inverse frequency transformer of a full audio decoder.

16. The transcoder of claim 9 wherein said partial audio decoder comprises an entropy decoder, an inverse quantizer, and a bark weighter.

17. The transcoder of claim 9 wherein said partial audio decoder further comprises an inverse channel transformer.

18. The transcoder of claim 9 wherein said partial audio decoder comprises an entropy decoder, and said intermediate state of said audio content is prior to inverse quantization.

19. A computer-readable storage media having computer executable instructions stored thereon for causing a computer to perform a method of transcoding an audio bitstream from an initially coded bit-rate to a target bit-rate, the method comprising:

receiving the audio bitstream from an audio encoder, the audio bitstream containing encoding parameters generated by the encoder for one or more encoding techniques employed by the encoder for encoding the audio bitstream from an audio input;

decoding the encoding parameters from the audio bitstream;

partially decoding audio content of the audio bitstream to an intermediate decoding stage prior to an inverse frequency transform;

adjusting the encoding parameters for the target bit-rate;

encoding the decoded audio content based on the encoding parameters adjusted for the target bit-rate; and

producing an output bitstream containing the encoded audio content.

20. The computer-readable storage medium of claim 19 wherein said encoding parameters comprise data characterizing a quality to quantization step size curve.