[FFmpeg-devel] [PATCH] AAC decoder round 8

[Robert Swain]

2008/8/15 Robert Swain <robert.swain at gmail.com>:
> 2008/8/15 Michael Niedermayer <michaelni at gmx.at>:
>> On Fri, Aug 15, 2008 at 09:04:24AM +0100, Robert Swain wrote:

[...]

>>> Index: libavcodec/aac.c
>>> ===================================================================
>>> --- libavcodec/aac.c  (revision 14774)
>>> +++ libavcodec/aac.c  (working copy)
>> [...]
>>> +
>>> +                for (i = 0; i < tns->order[w][filt]; i++)
>>> +                    tns->coef[w][filt][i] = get_bits(gb, coef_len);
>>
>> tns->coef is only used to index into tmp2_map thus
>> tns->coef could already contain the values from tmp2_map
>> this also would make the tmp2_map field unneeded in the struct
>
> OK, I'll look into this.

See attached. I assume this is what you mean.

[...]

>>> Index: libavcodec/aacdectab.h
>>> ===================================================================
>>> --- libavcodec/aacdectab.h    (revision 14767)
>>> +++ libavcodec/aacdectab.h    (working copy)
>
>>> +
>>> +/* @name tns_tmp2_map
>>> + * Tables of the tmp2[] arrays of LPC coefficients used for TNS.
>>> + * The suffix _M_N[] indicate the values of coef_compress and coef_res
>>> + * respectively.
>>> + * @{
>>> + */
>>> +static const float tns_tmp2_map_1_3[TNS_MAX_ORDER] = {
>>> +     0.00000000,  0.43388373, -0.64278758, -0.34202015,
>>> +     0.97492790,  0.78183150, -0.64278758, -0.34202015,
>>> +    -0.43388373, -0.78183150, -0.64278758, -0.34202015,
>>> +    -0.78183150, -0.43388373, -0.64278758, -0.34202015,
>>> +     0.78183150,  0.97492790, -0.64278758, -0.34202015
>>> +};
>>> +
>>> +static const float tns_tmp2_map_0_3[TNS_MAX_ORDER] = {
>>> +     0.00000000,  0.43388373,  0.78183150,  0.97492790,
>>> +    -0.98480773, -0.86602539, -0.64278758, -0.34202015,
>>> +    -0.43388373, -0.78183150, -0.97492790, -0.97492790,
>>> +    -0.98480773, -0.86602539, -0.64278758, -0.34202015,
>>> +     0.78183150,  0.97492790,  0.97492790,  0.78183150
>>> +};
>>> +
>>> +static const float tns_tmp2_map_1_4[TNS_MAX_ORDER] = {
>>> +     0.00000000,  0.20791170,  0.40673664,  0.58778524,
>>> +    -0.67369562, -0.52643216, -0.36124167, -0.18374951,
>>> +     0.99452192,  0.95105648,  0.86602539,  0.74314481,
>>> +    -0.67369562, -0.52643216, -0.36124167, -0.18374951,
>>> +    -0.20791176, -0.40673670, -0.58778530, -0.74314487
>>> +};
>>> +
>>> +static const float tns_tmp2_map_0_4[TNS_MAX_ORDER] = {
>>> +     0.00000000,  0.20791170,  0.40673664,  0.58778524,
>>> +     0.74314481,  0.86602539,  0.95105654,  0.99452192,
>>> +    -0.99573416, -0.96182561, -0.89516330, -0.79801720,
>>> +    -0.67369562, -0.52643216, -0.36124167, -0.18374951,
>>> +    -0.20791176, -0.40673670, -0.58778530, -0.74314487
>>> +};
>>
>> iam not sure if the code is correct but i think several of these
>> elements can never be accessed
>
> I'll check the code.

The current code only accesses elements 0-15 by my reckoning. I'm
working through the code for tns_decode_coef() in the spec to see if
it matches what we have here.

Rob
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