[FFmpeg-devel] [PATCH 1/6] ac3enc_fixed: convert to 32-bit sample format

[Andreas Rheinhardt]

Lynne:
> Jan 9, 2021, 22:01 by andreas.rheinhardt at gmail.com:
> 
>> Lynne:
>>
>>> @@ -165,7 +164,11 @@ typedef struct AC3EncodeContext {
>>>  AVCodecContext *avctx;                  ///< parent AVCodecContext
>>>  PutBitContext pb;                       ///< bitstream writer context
>>>  AudioDSPContext adsp;
>>> +#if AC3ENC_FLOAT
>>>  AVFloatDSPContext *fdsp;
>>> +#else
>>> +    AVFixedDSPContext *fdsp;
>>> +#endif
>>>  MECmpContext mecc;
>>>  AC3DSPContext ac3dsp;                   ///< AC-3 optimized functions
>>>  FFTContext mdct;                        ///< FFT context for MDCT calculation
>>>
>> [...]
>>
>>> @@ -118,9 +89,10 @@ static CoefType calc_cpl_coord(CoefSumType energy_ch, CoefSumType energy_cpl)
>>>  static av_cold void ac3_fixed_mdct_end(AC3EncodeContext *s)
>>>  {
>>>  ff_mdct_end(&s->mdct);
>>> +    av_freep(&s->fdsp);
>>> +    av_freep(&s->mdct_window);
>>>  }
>>>
>>
>> ff_ac3_encode_close already unconditionally frees fdsp, so freeing it
>> above is either unnecessary or ac3_float_mdct_end should also free its
>> fdsp (and ff_ac3_encode_close shouldn't). Freeing mdct_window can also
>> be moved to ff_ac3_encode_close (which already frees several buffers
>> whose pointed-to-type depends upon the encoding mode).
>> Notice that ac3enc.c uses the fixed-point mode, but the layout of
>> AC3EncodeContext does not depend upon this (apart from pointed-to-types,
>> of course). Actually, ff_mdct_end does the same for both fixed- and
>> floating-point mode, so one could even incorporate
>> ac3_fixed/float_mdct_end into ff_ac3_encode_close.
>>
> Done. Left ac3_fixed/float_mdct_end as-is for now.
> New patch attached.
> >
> @@ -129,8 +99,31 @@ static av_cold void ac3_fixed_mdct_end(AC3EncodeContext *s)
>   */
>  static av_cold int ac3_fixed_mdct_init(AC3EncodeContext *s)
>  {
> +    int32_t *iwin;
> +    float fwin[AC3_BLOCK_SIZE];
> +
>      int ret = ff_mdct_init(&s->mdct, 9, 0, -1.0);
> -    s->mdct_window = ff_ac3_window;

You forgot to remove this table.

> +    if (ret < 0)
> +        return ret;
> +
> +    iwin = av_malloc_array(AC3_WINDOW_SIZE, sizeof(*iwin));
> +    if (!iwin)
> +        return AVERROR(ENOMEM);
> +
> +    ff_kbd_window_init(fwin, 5.0, AC3_WINDOW_SIZE/2);
> +
> +    for (int i = 0; i < AC3_WINDOW_SIZE/2; i++)
> +        iwin[i] = lrintf(fwin[i] * (1 << 22));
> +

Does this lead to a different result than using ff_kbd_window_init_fixed
directly?

> +    for (int i = 0; i < AC3_WINDOW_SIZE/2; i++)
> +        iwin[AC3_WINDOW_SIZE-1-i] = iwin[i];
> +
> +    s->mdct_window = iwin;
> +
> +    s->fdsp = avpriv_alloc_fixed_dsp(s->avctx->flags & AV_CODEC_FLAG_BITEXACT);
> +    if (!s->fdsp)
> +        return AVERROR(ENOMEM);
> +
>      return ret;
>  }