[FFmpeg-devel] [PATCH v2 8/8] aacdec: add a decoder for AAC USAC (xHE-AAC)

[Marton Balint]

On Wed, 22 May 2024, Lynne via ffmpeg-devel wrote:

> On 21/05/2024 23:33, Hendrik Leppkes wrote:
>>  On Tue, May 21, 2024 at 9:52 PM Lynne via ffmpeg-devel
>>  <ffmpeg-devel at ffmpeg.org> wrote:
>>> 
>>>
>>>  It should be the case here, we shouldn't need reordering as NATIVE just
>>>  lets you specify what order the elements appear in the bitstream.
>>
>>  NATIVE means "the FFmpeg native ordering", not "bitstream order".
>>  CUSTOM lets you specify an arbitrary order but requires metadata to
>>  that effect, but it makes it particularly hard to map to any standard
>>  when playing or transcoding, so some efforts to try to unify it into a
>>  NATIVE format is always appreciated if possible.
>
> Right, I forgot about that, thanks.
> Amended in my git repo to use Marton's code.
>
>

> ret = av_channel_layout_custom_init(&ac->oc[1].ch_layout, nb_channels);
> if (ret < 0)
>     return ret;
> 
> for (int i = 0; i < nb_channels; i++) {
>     AVChannelCustom *cm = &ac->oc[1].ch_layout.u.map[i];
>     cm->id = usac_ch_pos_to_av[get_bits(gb, 5)]; /* bsOutputChannelPos */
>     if (cm->id)
>         cm->id = AV_CHAN_UNKNOWN;

if (cm->id == AV_CHAN_NONE)
     cm->id = AV_CHAN_UNKNOWN;

> }
> 
> ret = av_channel_layout_retype(&ac->oc[1].ch_layout,
>                                AV_CHANNEL_ORDER_NATIVE,
>                                AV_CHANNEL_LAYOUT_RETYPE_FLAG_CANONICAL);

You can simply pass 0 instead of AV_CHANNEL_ORDER_NATIVE as the order 
parameter, because AV_CHANNEL_LAYOUT_RETYPE_FLAG_CANONICAL automatically 
uses the canonical order and ignores the order parameter.

> if (ret < 0)
>     return ret;
> 
> av_channel_layout_copy(&avctx->ch_layout, &ac->oc[1].ch_layout);

Missing error check.

Thanks,
Marton