_äìé`çêé. Audio Compression Codec Specifications and Requirements. Application Note. Issue 2

Transcription

1 _äìé`çêé Audio Compression Codec Specifications and Requirements Application Note Issue 2 CSR Cambridge Science Park Milton Road Cambridge CB4 0WH United Kingdom Registered in England Tel: +44 (0) Fax: +44 (0)

2 Contents Contents 1 Introduction Codecs Compliance SBC CODEC Requirements Software Used SBC Memory Requirements SBC MIPS and Power Requirements SBC Decoder Compliance SBC Encoder Compliance SBC Support SBC Codec Usage Functions Messages Example Applications MP3 Codec Requirements Software Used MP3 Memory Requirements MP3 MIPS and Power Requirements MP3 Decoder Compliance MP3 Support MP3 Codec Usage Functions Messages Example Applications AAC CODEC Requirements Software Used AAC Decoder Memory Requirements AAC MIPS and Power Requirements AAC Decoder Compliance AAC-LC AAC HEV AAC HEV AAC Support AAC Codec Usage Functions Messages Example Applications List of Figures Figure 2.1: Test Set-up... 9 List of Tables Table 2.1: SBC Memory Requirements... 5 Table 2.2:SBC Decoder Power and MIPS Requirements... 5 Table 2.3: SBC Encoder Power and MIPS Requirements... 6 Table 2.4: SBC Decoder Compliance... 7 Page 2 of 27

3 Contents Table 2.5: SBC Encoder Compliance... 8 Table 2.6: SBC Support Table 2.7: SBC Codec Functions Table 2.8: SBC Codec Messages Table 2.9: SBC Codec Example Applications Table 3.1: MP3 Memory Requirements Table 3.2: MP3 Decoder Power and MIPS Requirements Table 3.3: MP3 Encoder Power and MIPS Requirements Table 3.4: MP3 Decoder Compliance Table 3.5: MP3 Support Table 3.6: MP3 Codec Functions Table 3.7: MP3 Codec Messages Table 3.8: MP3 Codec Example Applications Table 4.1: AAC Memory Requirements Table 4.2: AAC Decoder Power and MIPS Requirements Table 4.3: AAC LC Decoder Compliance Table 4.4: AAC HEV1 Decoder Compliance Table 4.5: AAC HEV2 Decoder Compliance Table 4.6: AAC Support Table 4.7: AAC Codec Functions Table 4.8: AAC Codec Messages Table 4.9: AAC Codec Example Applications Page 3 of 27

4 Introduction 1 Introduction This document describes the technical capabilities and performance specifications of the audio decoders and encoders supplied by CSR for=_äìé`çêé RJjìäíáãÉÇá~. CSR has developed a family of fast, high quality audio decoder and encoder libraries. They are intended to be integrated into DSP applications running on BlueCore5-Multimedia, for example to stream audio using the Advanced Audio Distribution Profile (A2DP) Bluetooth wireless technology profile or for direct local playback from files. 1.1 Codecs This document describes MP3, SBC and AAC codecs: MP3 is a widely used audio compression standard, designed for generic mono or stereo audio. At 128kpbs, with a compression ratio of about 11:1, the quality is subjectively similar to compact disc. SBC is the mandatory codec specified in the A2DP Bluetooth profile designed to ensure interoperability. It is a low complexity sub-band codec achieving a compression ratio of about 5:1 for high-quality stereo. AAC is another popular high quality codec, originally designed to be the successor of MP3. AAC and its variants generally achieve better sound quality than MP3 at lower bitrates. 1.2 Compliance All codecs described in this document have been tested and pass compliance testing procedures required for supported functionality. Additionally, all codecs have been tested with an extensive number of test cases, covering a diverse range of audio and bitstream sources, to ensure predictable functionality and accepted quality. Page 4 of 27

5 SBC CODEC Requirements 2 SBC CODEC Requirements 2.1 Software Used BlueLab v4.1 release candidate software 2.2 SBC Memory Requirements Module Library (.klib) PM words (32bit) RAM Flash RAM (24bit) DM words Decoder only sbc Encoder only sbc Encoder and Decoder combined sbc Table 2.1: SBC Memory Requirements Flash (16bit) Notes: The figures in Table 2.1 do not include the audio or SBC buffers. Recommended sizes for a Bluetooth AV link are 0.32Kwords data memory (DM) per audio channel; 1K-4Kwords DM per SBC stream (depending on the maximum jitter to support). The figures in Table 2.1 do not include the standard libraries that are also required for a complete application (i.e. stack, timer, message, cbuffer, codec, cbops). These are approximately 1100words program memory (PM) and 300 words DM. 2.3 SBC MIPS and Power Requirements Decoder Settings MCPS MIPS Ave Peak Ave Peak 1.8V Approximate (ma) Mono, 16 KHz, 64 kbps Joint Stereo, 44.1KHz, Middle Quality (250kbit/s) Joint Stereo, 44.1KHz, High Quality (350kbit/s) Table 2.2: SBC Decoder Power and MIPS Requirements Note: The figures in Table 2.2 are for the SBC decoder module only. They do not include the routines to get data into and out of the DSP from the rest of the BlueCore subsystem (if the XAP is running at full-speed assume 3 clock cycles for this). The peak MCPS and MIPS figures in Table 2.2 are the maximum measured for a frame (3 ms at 44.1 khz and 8 ms at 16 khz). Page 5 of 27

6 SBC CODEC Requirements Encoder Settings MCPS MIPS Ave Peak Ave Peak 1.8V Approximate (ma) Mono, 16 KHz, (64 kbit/s) Joint Stereo, 44.1KHz, Middle Quality (250 kbit/s) Joint Stereo, 44.1KHz, High Quality (350 kbit/s) Table 2.3: SBC Encoder Power and MIPS Requirements Note: The figures in Table 2.3 are for the SBC encoder module only. They do not include the routines to get data into and out of the DSP from the rest of the BlueCore subsystem (if the XAP is running at full-speed assume 3 clock cycles for this). The peak MCPS and MIPS figures in Table 2.3 are the maximum measured for a frame (3 ms at 44.1 khz and 8 ms at 16 khz). Page 6 of 27

7 SBC CODEC Requirements 2.4 SBC Decoder Compliance Conformance Test File Max LSB Error (Bit) Left/Mono RMS Error (Bit) Max LSB Error Right RMS Error Overall Accuracy Level (K) sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ K=17 sbc_test_ Mono Mono K=17 sbc_test_ Mono Mono K=17 sbc_test_ K=17 sbc_test_ K=17 Table 2.4: SBC Decoder Compliance Note: The Bluetooth specification for A2DP suggests a minimum accuracy level of K=14. Page 7 of 27

8 SBC CODEC Requirements 2.5 SBC Encoder Compliance Conformance Test Using Settings from RMS Difference Between Original Wav and Reference Output (db) RMS Difference Between Original Wav and Kalimba Output (db) Difference Between Reference and Kalimba Encoder (db) Negative is Worse sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ sbc_test_ Table 2.5: SBC Encoder Compliance Note: The Bluetooth specification for A2DP suggests that the quality of the encoder under test should be equivalent to that of the reference. Figure 2.1 shows the test set-up that was used. Page 8 of 27

9 SBC CODEC Requirements Original Wav Reference Encoder Temp Reference Decoder Reference Output Original Wav Kalimba Encoder Calculate RMS Difference Temp Calculate RMS Difference Reference Decoder Figure 2.1: Test Set-up Kalimba Output Calculate difference to measure quality of Kalimba SBC Encoder Page 9 of 27

10 SBC CODEC Requirements 2.6 SBC Support Support in Decoder Support in Encoder Sampling Frequency (Hz) YES YES YES YES YES YES YES YES Channel Mode Mono YES YES Dual Channel YES YES Stereo YES YES Joint Stereo YES YES Block Length 4 YES YES 8 YES YES 12 YES YES 16 YES YES Number of Sub-bands 4 YES YES 8 YES YES Allocation method SNR YES YES Loudness YES YES Bit Pool Minimum to Maximum of the Spec (2 to 250) YES YES Table 2.6: SBC Support Page 10 of 27

11 SBC CODEC Requirements 2.7 SBC Codec Usage This section gives an overview of the SBC codec API: Functions Module Function Description Decoder Encoder $sbcdec.init_decoder $sbcdec.reset_decoder $sbcdec.silence_decoder $sbcdec.frame_decode $sbcenc.init_encoder $sbcenc.reset_encoder $sbcenc.frame_encode Messages SBC codec receives several messages from the VM: Initialises the decoder, and registers its message handlers. Call once at the beginning of application. Resets the internal state of the decoder Silences the internal state of the decoder so that no pops and squeaks are generated upon re-enabling/resuming the output audio The main function for decoding a frame from the SBC stream Initialises the encoder, and registers its message handlers. Call once at the beginning of application. Resets the internal state of the encoder The main function for encoding a frame of audio into SBC bitstream Table 2.7: SBC Codec Functions Module Message Description Decoder MESSAGE_SBCDEC_CONVERT_TO_MONO Enable/Disable conversion to mono Encoder MESSAGE_SBCENC_SET_BITPOOL MESSAGE_SBCENC_SET_PARAMS Table 2.8: SBC Codec Messages Used for setting the bit pool value Used for setting other encoder parameters Page 11 of 27

12 SBC CODEC Requirements Example Applications Table 2.9 lists the example applications shipped with BlueLab 4.1 that use the SBC codec: Example Application test_sbcloopback test_mp3sbcloopback test_graphix_driver Description This application gets the audio from ADCs encodes it to SBC, then decodes the results and outputs the audio over DACs Same as test_sbcloopback, but also demonstrating the mp3 library at the same time Same as test_sbcloopback, but also demonstrating the graphix library at the same time Table 2.9: SBC Codec Example Applications Page 12 of 27

13 MP3 Codec Requirements 3 MP3 Codec Requirements 3.1 Software Used BlueLab v4.1 release candidate software 3.2 MP3 Memory Requirements Module Library (.klib) PM Words (32bit) RAM Flash RAM (24bit) DM Words Flash (16bit) Decoder only mp Decoder only Flash Version mp3_flash Encoder only mp3enc Encoder only Flash Version mp3enc_flash Table 3.1: MP3 Memory Requirements Notes: The figures in Table 3.1 do not include the audio or MP3 buffers. Recommended sizes for a Bluetooth AV link are 1.152Kwords DM per audio channel; 0.75K-3Kwords DM per MP3 stream (depending on the maximum jitter to support). The figures in Table 3.1 do not include the standard libraries that are also required for a complete application (i.e. stack, timer, message, cbuffer, codec, cbops). These are approximately 1100words PM and 300 words DM. 3.3 MP3 MIPS and Power Requirements Decoder Settings Library (.klib) MCPS MIPS Ave Peak Ave Peak 1.8V Approximate (ma) Stereo, 44.1KHz, 128kbps mp Stereo, 44.1KHz, 320kbps mp Mono, 16kHz, 64kbps mp Stereo, 44.1KHz, 128kbps mp3_flash Stereo, 44.1KHz, 320kbps mp3_flash Mono, 16kHz, 64kbps mp3_flash Table 3.2: MP3 Decoder Power and MIPS Requirements Note: The figures in Table 3.2 are for the MP3 decoder module only. They do not include the routines to get data into and out of the DSP from the rest of the BlueCore subsystem (if the XAP is running at full-speed assume 3 clock cycles for this). The peak MCPS and MIPS figures in Table 3.2 are the maximum measured for a frame (13 ms at 44.1 khz and 36 ms at 16 khz). Page 13 of 27

14 MP3 Codec Requirements Encoder Settings Setting Word Library (.klib) MCPS MIPS Ave Peak Ave Peak Approximate (ma) Joint Stereo, 44.1KHz, 128kbps CBR 0x99F Joint Stereo, 44.1KHz, 160kbps CBR 0xAAF Joint Stereo, 44.1KHz, 320kbps CBR 0xEEF Joint Stereo, 44.1KHz, 160kbps ABR 0xE1F Mono, 16kHz, 64kbps CBR (MPEG2) 0x Joint Stereo, 44.1KHz, 128kbps CBR 0x99F Joint Stereo, 44.1KHz, 160kbps CBR 0xAAF Joint Stereo, 44.1KHz, 320kbps CBR 0xEEF Joint Stereo, 44.1KHz, 160kbps ABR 0xE1F Mono, 16kHz, 64kbps CBR (MPEG2) 0x mp3enc mp3enc_flash Table 3.3: MP3 Encoder Power and MIPS Requirements Note: ABR = Average bitrate. That is, the encoder tries to maintain and average output bitrate, but allows different packet sizes to be used. If not mentioned, constant bitrate (CBR) encoding is used. The figures in Table 3.3 are for the MP3 encoder module only. They do not include the routines to get data into and out of the DSP from the rest of the BlueCore subsystem (if the XAP is running at full-speed assume 3 clock cycles for this). The peak MCPS and MIPS figures in Table 3.3 are the maximum measured for a frame (13 ms at 44.1 khz and 36 ms at 16 khz). Page 14 of 27

15 MP3 Codec Requirements 3.4 MP3 Decoder Compliance Reference decoder used: l3dec v3.0. Additional Test Files Conformance Test File Max LSB Error (bits) Left/Mono RMS Error (bits) Max LSB Error (bits) Right RMS Error (bits) Overall Accuracy Level K Compl.mp Mono Mono 15.9 he_32khz.mp Mono Mono 16.5 he_44khz.mp Mono Mono 16.5 he_48khz.mp Mono Mono 16.5 he_mode_mono.mp Mono Mono 16.4 he_mode_stereo.mp hecommon.mp si.mp Mono Mono 16.9 si_block.mp Mono Mono 16.8 sin1k0db.mp Shania.mp3 (music 3-4min) Flower.mp3 (music 3-4min) Table 3.4: MP3 Decoder Compliance Page 15 of 27

16 MP3 Codec Requirements 3.5 MP3 Support Support in Decoder Support in Encoder Supported Layer 3 3 Supported Versions MPEG 1, 2, 2.5 MPEG 1, 2, 2.5 Supported Sampling Frequencies (khz) Bit Rates (kbps) Channel Mode Notes: MPEG 1 MPEG 2, 2.5 8, , 12, 16, 22.05, 24, 32, 44.1, 48 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 Mono, Stereo, Joint Stereo, Dual channel Table 3.5: MP3 Support 8, , 12, 16, 22.05, 24, 32, 44.1, 48 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 Mono, Stereo, Joint Stereo 1. Both constant bitrate (CBR) and variable bitrate (VBR) are supported for the encoder and decoder in all supported versions. 2. Free format bitrate is not supported. Page 16 of 27

17 MP3 Codec Requirements 3.6 MP3 Codec Usage This section provides an overview of the MP3 codec API: Functions Module Function Description Decoder Encoder $mp3dec.init_decoder $mp3dec.reset_decoder $mp3dec.silence_decoder $mp3dec.frame_decode $mp3dec.suspend_decoder $mp3dec.store_boundary_snapshot $mp3dec.resume_decoder $mp3dec.restore_boundary_snapshot $mp3enc.init_encoder $mp3enc.reset_encoder $mp3enc.frame_encode Table 3.6: MP3 Codec Functions Initialises the decoder. Call once at the beginning of application. Resets internal state of the decoder Silences the internal state of the decoder so that no pops and squeaks are generated upon reenabling/resuming the output audio The main function for decoding a frame from the MP3 stream Store the internal state of the decoder. See notes Store the instantaneous internal state of the decoder Restore the internal state of the decoder Restore the instantaneous internal state of the decoder Initialises the encoder, and registers its message handlers. Call once at the beginning of application. Resets internal state of the encoder The main function for encoding a frame of audio into MP3 bitstream Notes: The suspend function stores the entire internal state of the decoder. After resume, the decoder should be able to continue decoding given the stream position is restored as well. This can be used for scenarios where a stream is interrupted (e.g. end user is listening to music when a call comes in and a new application is loaded). In contrast, re/store boundary snapshot functions only store instantaneous state of the decoder (i.e. not the stable state which is dependent on the stream like sampling frequency). These functions may be used for navigating in the stream (e.g. rewind) given the stream position is also restored correctly. Page 17 of 27

18 MP3 Codec Requirements Messages MP3 codec receives several messages from the VM: Module Message Description Encoder MESSAGE_MP3ENC_SET_PARAMS Used for setting encoder parameters Example Applications Table 3.7: MP3 Codec Messages Table 3.8 shows the example applications shipped with Bluelab 4.1 that use the MP3 codec: Example Application test_mp3decoder test_mp3sbcloopback Description This application reads an MP3 file from the filesystem, then decodes the results and outputs the audio over DACs Using either SBC or MP3, test_mp3sbcloopback takes audio from USB, encodes and decodes it using the selected format, and outputs the audio over the DACs Table 3.8: MP3 Codec Example Applications Page 18 of 27

19 AAC CODEC Requirements 4 AAC CODEC Requirements 4.1 Software Used BlueLab v4.1 release candidate software 4.2 AAC Decoder Memory Requirements Module AAC LC AAC HE V1 AAC HE V2 PM words (32bit) DM words Library (.klib) RAM Flash RAM Flash (24bit) (16bit) aac math aac_plusv math aac_plusv math Table 4.1: AAC Memory Requirements Notes: The figures in Table 4.1 do not include the audio or AAC buffers. Recommended sizes for a Bluetooth AV link are 2.56Kwords DM per audio channel; 0.75K-3Kwords DM per AAC stream (depending on the maximum jitter to support). The figures in Table 4.1do not include the standard libraries that are also required for a complete application (i.e. stack, timer, message, cbuffer, codec, cbops). These are approximately 1100words PM and 300 words DM. The math library is required by all supported AAC versions and its memory requirements in each case is given. The aac library is a subset of the aac_plusv1 library, which in turn is a subset of the aac_plusv2 library. 4.3 AAC MIPS and Power Requirements Decoder Settings Library (.klib) MCPS MIPS Ave Peak Ave Peak 1.8V Approximate (ma) Stereo, 44.1KHz, 320 kbps ADTS aac Stereo, 44.1KHz, 128 kbps ADTS aac Stereo, 44.1KHz, 128 kbps MP4 aac Stereo, 44.1 khz, 64 kbps ADTS aac Stereo, 44.1KHz, 96 kbps ADTS aac_plusv Stereo, 44.1KHz, 64 kbps ADTS aac_plusv Stereo, 44.1KHz, 32 kbps ADTS aac_plusv Stereo, 44.1KHz, 24 kbps ADTS aac_plusv Table 4.2: AAC Decoder Power and MIPS Requirements Note: The figures in Table 4.2 are for the AAC decoder module only (including the math library). They do not include the routines to get data into and out of the DSP from the rest of the BlueCore subsystem (if the XAP is running at full-speed assume 3 clock cycles for this). Page 19 of 27

20 AAC CODEC Requirements The peak MCPS and MIPS figures in Table 4.2 are the maximum measured for a frame (23 ms). 4.4 AAC Decoder Compliance AAC-LC Conformance Test File Max LSB Error (Bit) Left/Mono RMS Error (Bit) Max LSB Error Right RMS Error al00_8k Mono Mono al00_11k Mono Mono al00_12k Mono Mono al00_16k Mono Mono al00_22k Mono Mono al00_24k Mono Mono al00_32k Mono Mono al00_44k Mono Mono al00_48k Mono Mono al18_8k al18_11k025 al18_12k al18_16k al18_22k05 al18_24k PNS testing tool used for testing. All files pass PNS-1 test procedure. al18_32k al18_44k1 al18_48k al18_8k al19_8k al19_11k025 al19_12k al19_16k PNS testing tool used for testing. al19_22k05 All files pass PNS-2/3 test procedure. al19_24k al19_32k al19_44k1 al19_48k Table 4.3: AAC LC Decoder Compliance Page 20 of 27

21 AAC CODEC Requirements AAC HEV1 Left/Mono Right Conformance Test File Max LSB Error (Bit) RMS Error (Bit) Max LSB Error (bits) RMS Error al_sbr_cm_48_ Mono Mono al_sbr_cm_48_ al_sbr_e_32_ Mono Mono al_sbr_e_32_ al_sbr_e_44_ Mono Mono al_sbr_e_44_ al_sbr_e_48_ Mono Mono al_sbr_e_48_ al_sbr_gh_32_ Mono Mono al_sbr_gh_32_ al_sbr_gh_44_ Mono Mono al_sbr_gh_44_ al_sbr_gh_48_ Mono Mono al_sbr_gh_48_ al_sbr_i_32_ Mono Mono al_sbr_i_32_ Mono Mono al_sbr_i_44_ Mono Mono al_sbr_i_44_ Mono Mono al_sbr_i_48_ Mono Mono al_sbr_i_48_ Mono Mono al_sbr_s_32_ Mono Mono al_sbr_s_32_ al_sbr_s_44_ Mono Mono al_sbr_s_44_ al_sbr_s_48_ Mono Mono al_sbr_s_48_ al_sbr_qmf_32_ Mono Mono al_sbr_qmf_44_ Mono Mono al_sbr_qmf_48_ Mono Mono al_sbr_sig_48_2_sig al_sbr_sig_48_2_sig al_sbr_sig_48_2_sig al_sbr_sr_16_2_fsaac al_sbr_sr_22_2_fsaac al_sbr_sr_24_2_fsaac al_sbr_sr_32_2_fsaac al_sbr_sr_44_2_fsaac al_sbr_sr_48_2_fsaac al_sbr_sr_64_2_fsaac Page 21 of 27

22 AAC CODEC Requirements al_sbr_sr_88_2_fsaac al_sbr_sr_96_2_fsaac al_sbr_twi_48_1_fsaac Mono Mono AAC HEV2 Conformance Test File Table 4.4: AAC HEV1 Decoder Compliance Max LSB Error (bits) Left/Mono RMS Error (bits) Max LSB Error (bits) Right RMS Error (bits) al_sbr_ps_ Mono Mono al_sbr_ps_ al_sbr_ps_ al_sbr_ps_ al_sbr_ps_ Mono Mono al_sbr_ps_ al_sbr_ps_ AAC Support Table 4.5: AAC HEV2 Decoder Compliance Support in Decoder Sampling Frequency 8, , 12, 16, 22.05, 24, 32, 44.1, 48, 64, 88.2, 96 Channels Mono, Stereo, Joint Stereo, Dual Channel Bitrates All bitrates supported Bitstream Formats MP4, ADTS Notes: 1. Down-sampled SBR not supported 2. Only up to two channels supported Table 4.6: AAC Support Page 22 of 27

23 AAC CODEC Requirements 4.6 AAC Codec Usage This section gives an overview of the AAC codec API: Functions Function $aacdec.init_decoder $aacdec.reset_decoder $aacdec.silence_decoder $aacdec.frame_decode $aacdec.suspend_decoder $aacdec.store_boundary_snapshot $aacdec.resume_decoder $aacdec.restore_boundary_snapshot Description Initialises the decoder. Call once at the beginning of application. Resets the internal state of the decoder Silences the internal state of the decoder so that no pops and squeaks are generated upon re-enabling/resuming the output audio The main function for decoding a frame from the AAC stream Store the internal state of the decoder Store the instantaneous internal state of the decoder Restore the internal state of the decoder Restore the instantaneous internal state of the decoder Table 4.7: AAC Codec Functions Notes: The stream type needs to have been selected before calling this function. This could be done via a message from VM. The suspend function stores the entire internal state of the decoder. After resume, the decoder should be able to continue decoding given the stream position is restored as well. This can be used for scenarios where a stream is interrupted (e.g. end user is listening to music when a call come in and a new application is loaded). In contrast, re/store boundary snapshot functions only store instantaneous state of the decoder (i.e. not the stable state which is dependent on the stream like sampling frequency). These functions may be used for navigating in the stream (e.g. rewind) given the stream position is also restored correctly Messages AAC codec receives one message from the VM: Message MESSAGE_AACDEC_SET_FILE_TYPE Description Used for setting the stream type (e.g. ADTS, MP4) Table 4.8: AAC Codec Messages Page 23 of 27

24 AAC CODEC Requirements Example Applications Table 3.8 shows the example application shipped with Bluelab 4.1 that uses the AAC codec: Example Application test_aacdecoder Description This application reads an AAC file from the filesystem, then decodes the results and outputs the audio over DACs Table 4.9: AAC Codec Example Applications Page 24 of 27

25 Error! No text of specified style in document. Terms and Definitions A2DP AAC HEV1 AAC HEv2 AAC LC ABR ADC ADTS API BlueCore BlueLab Bluetooth CODEC CBR CSR DAC DM DSP e.g. i.e. LSB MCPS MIPS PM PNS PS RMS SBC SBR SNR VBR VM Advanced Audio Distribution Profile Advanced audio coding high efficiency version 1 (an extension of AAC that supports Subband Replication (SBR) coding) Advanced audio coding high efficiency version 2 (an extension of AAC HEV1 that supports Parametric Stereo (PS) coding) Advanced audio coding low complexity Average Bitrate Analogue to Digital Converter Audio Data Transport Stream Application Programming Interface Group term for CSR s range of Bluetooth wireless technology chips CSR s development toolset for building applications to run in the firmware s Virtual Machine Set of technologies providing audio and data transfer over short-range radio connections COder DECoder Constant Bitrate Cambridge Silicon Radio Digital to Analogue Converter Data Memory Digital Signal Processor exempli gratia, for example Id est, that is Least Significant Bit Million clocks per second Million instructions per second Program Memory Perceptual Noise Substitution Parametric Stereo Root Mean Squared Sub-band Coding Sub-band Replication Signal-to-Noise Ratio Variable Bitrate Virtual Machine Page 25 of 27

26 Document References Document References Document Reference Specification of the Bluetooth System v1.2, Profiles, 05 November 2003 Page 26 of 27

27 Document History Document History Revision Date History Issue 1 16 OCT 08 Original publication of this document. Issue 2 16 OCT 08 Decoder Power and MIPS Requirements tables updated Document Feedback If you have any comments about this document, send an to comments@csr.com, giving the document number, title and section with your feedback. Unless otherwise stated, words and logos marked with or are trademarks registered or owned by Cambridge Silicon Radio Limited or its affiliates. Bluetooth and the Bluetooth logos are trademarks owned by Bluetooth SIG, Inc. and licensed to CSR. Other products, services and names used in this document may have been trademarked by their respective owners. The publication of this information does not imply that any licence is granted under any patent or other rights owned by Cambridge Silicon Radio Limited. CSR reserves the right to make technical changes to its products as part of its development programme. While every care has been taken to ensure the accuracy of the contents of this document, CSR cannot accept responsibility for any errors. CSR s products are not authorised for use in life-support or safety-critical applications. Refer to for compliance and conformance to standards information. Page 27 of 27