Changing Audio Bitrate to CBR

Sean, K.

Hi,

we use AAC encoder to generate CBR AAC audio in DM368 using DVSDK.

We found IAUDIO_CBR option was set default in the sample code.

However, the result AAC is in VBR. Its ADTS header indicates it is VBR (0x7FF),
Also in audio players it detected as VBR.

Our engineer changed the option from IAUDIO_CBR to IAUDIO_VBR, to see how the result would be, but there was an error message in runtime.

How do I make AAC files in CBR?

Thanks in advance for your reply.

over 14 years ago

0 Raja Shekara over 14 years ago

TI__Prodigy 350 points

Hi Sean,

Encoder will insert 0x7ff in buffer_fullness field only incase of VBR encoding mode.

Can you please let me know the parameter settings(both creation and dynamic paramas).

Also please share a small stream which has 0x7ff in bufferfullness field for CBR mode.

Ram

0 Sean, K. over 14 years ago in reply to Raja Shekara

Prodigy 150 points

Hi Raja,

I uploaded a file here. (it's mono sound yet)

0334.0214Target2.aac

also in my web disk (it's from evaluation board, stereo):

http://public.bay.livefilestore.com/y1pGNKumRASM1uGjoujkhqfZKcXNOpVCTNkDYwbKTtANjt_rBboOnZbE4rZuriIpiZCJSYXkNirSsK8R_KasWYbBw/0214testEVM.aac?download&psid=1

Always the bufferfullness field in the header is 0x7FF.

And the Parameter Settings are below:

const AUDENC1_Params Aenc1_Params_DEFAULT = {
sizeof(AUDENC1_Params),
48000,

288000,

IAUDIO_2_0,

    XDM_LE_16,
    IAUDIO_CBR,
    IAUDIO_INTERLEAVED,
    16,
    192000,
    IAUDIO_DUALMONO_LR,
    XDAS_FALSE,
    XDAS_FALSE,
    XDAS_FALSE
};

const AUDENC1_DynamicParams Aenc1_DynamicParams_DEFAULT = {
sizeof(AUDENC1_DynamicParams),
288000,

48000,

   IAUDIO_2_0,//IAUDIO_2_0,
    XDAS_FALSE,
    IAUDIO_DUALMONO_LR,
    16
};

0 Ramprasad over 14 years ago in reply to Sean, K.

TI__Mastermind 30480 points

Hi Sean,

I am observing 0x7ff in buffer-fullness field for both the aac streams.

Parameter setting is 48kHz at 288kbps, but the both the streams are encoded as 44.1kHz at 96kbps.

Are these encoded as 44.1kHz at 96kbps? How are these set?

Ram

0 Sean, K. over 14 years ago in reply to Ramprasad

Prodigy 150 points

Hi Ramprasad,

That was because our engineer keeps changing the options for test.
there's no difference other than those settings, 44.1kHz at 96kbps.

so could you please analyze those files and
give me the answer?

PS. actually the file in 48kHz at 288kbps is here:

http://www.mediafire.com/?c531i586fjx1sjd

but the sound is dirty for some reason, so I couldn't upload it for you.
(probably it might be the next question)

Thank you for the help.

0 Sean, K. over 14 years ago in reply to Sean, K.

Prodigy 150 points

I found that only CBR mode is supported in Audio, from this document.

Document Name : IA-HEAACv2-Enc-XDM
Version : 1.0
Date : September 28, 2008

and its description is

encMode : Encoding mode. Only IAUDIO_CBR is supported.

If it is, how did I get 0x7FF in the AAC file generated?

0 Ramprasad over 14 years ago in reply to Sean, K.

TI__Mastermind 30480 points

Hi Sean,

Sorry I thought the AACEncoder is on C64x+ platform. On c64x+ platform, encoder supports both CBR and VBR.

For information on codecs on ARM please contact venkatv@ti.com

Ram

0 Sean, K. over 14 years ago in reply to Ramprasad

Prodigy 150 points

Thanks a lot, Ram.

I'll contact him.

0 mark3778 mark3778 over 14 years ago in reply to Sean, K.

Prodigy 10 points

thanks for the useful information

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Changing Audio Bitrate to CBR