[FFmpeg-devel] [PATCH 0/5 v2] 22.2 channel layout support for AAC decoding

[Lynne]

Jul 29, 2020, 13:39 by jeebjp at gmail.com:

> Now that we actually have sample(s) for channel_config 13, it was possible
> to see at which various points the AAC decoder fails attempting to parse
> the bit stream.
>
> As the feature `-request_channel_layout 9223372036854775808` (AV_CH_LAYOUT_NATIVE)
> seems to work, the channel order has been validated both visually with
> Audacity, as well as by logging the post-reorder element ordering:
>
> (what specific CPE/SCE/LFE elements mean is documented in the
> `avcodec/aacdectab: add mapping for 22.2` commit):
>
> Setting layout map list after reorder...
> tag 0 = { pos: (null) (3), syn_elem: CPE, elem_id: 1 }
> tag 1 = { pos: FC (4), syn_elem: SCE, elem_id: 0 }
> tag 2 = { pos: LFE (8), syn_elem: LFE, elem_id: 0 }
> tag 3 = { pos: (null) (30), syn_elem: CPE, elem_id: 3 }
> tag 4 = { pos: (null) (c0), syn_elem: CPE, elem_id: 0 }
> tag 5 = { pos: BC (100), syn_elem: SCE, elem_id: 1 }
> tag 6 = { pos: LFE2 (800000000), syn_elem: LFE, elem_id: 1 }
> tag 7 = { pos: (null) (600), syn_elem: CPE, elem_id: 2 }
> tag 8 = { pos: (null) (5000), syn_elem: CPE, elem_id: 4 }
> tag 9 = { pos: TFC (2000), syn_elem: SCE, elem_id: 2 }
> tag 10 = { pos: TC (800), syn_elem: SCE, elem_id: 3 }
> tag 11 = { pos: (null) (28000), syn_elem: CPE, elem_id: 6 }
> tag 12 = { pos: (null) (3000000000), syn_elem: CPE, elem_id: 5 }
> tag 13 = { pos: TBC (10000), syn_elem: SCE, elem_id: 4 }
> tag 14 = { pos: BFC (8000000000), syn_elem: SCE, elem_id: 5 }
> tag 15 = { pos: (null) (14000000000), syn_elem: CPE, elem_id: 7 }
>
> swresample seems to give out the correct channels for 5.1 and stereo
> downmix (checked with ffmpeg.c by utilizing `-channel_layout` 5.1 and stereo),
> although the default downmix logic seems to lower the volume somewhat.
>
> Fixes #8714
>
> Jan Ekström (5):
>  avutil/channel_layout: add 22.2 layout
>  avcodec/mpeg4audio: add newer channel_coding mappings
>  avcodec/aacdectab: add mapping for 22.2
>  avcodec/aacdec_template: mark second LFE element as LFE2
>  avcodec/aacdec_template: add support for 22.2 / channel_config 13
>
>  doc/APIchanges               |  5 ++
>  libavcodec/aacdec_template.c | 98 ++++++++++++++++++++++++++++++++----
>  libavcodec/aacdectab.h       | 23 ++++++++-
>  libavcodec/mpeg4audio.c      | 17 ++++++-
>  libavcodec/mpeg4audio.h      |  2 +-
>  libavutil/channel_layout.c   |  6 +++
>  libavutil/channel_layout.h   |  6 +++
>  libavutil/version.h          |  2 +-
>  8 files changed, 142 insertions(+), 17 deletions(-)
>

Patchset looks good to me.