On Sun, 23 Mar 2025, James Almer wrote:
On 3/23/2025 4:33 PM, Massimo Eynard wrote:
On 23/03/2025 20:01, James Almer wrote:
On 3/22/2025 2:49 PM, Massimo Eynard wrote:
This patch adds support for decoding the fourth MLP substream
which contains the 16-channel presentation used for Atmos
audio objects.
By default only the first three substreams are decoded
unless the new extract_objects flag is enabled as the resulting
presentation contains audio object feeds instead of classic
loudspeaker feeds.
As this introduces interpolation of primitive matrices, precision
has been increased to 2.18 fixed point. Therefore this requires
DSP code upgrade which has been done for C and x86 implementations
but not the ARM implementation.
Adds two FATE tests using existing atmos.thd sample to reflect
changes.
Signed-off-by: Massimo Eynard <eynard.mass...@gmail.com>
---
libavcodec/arm/mlpdsp_armv5te.S | 2 +-
libavcodec/arm/mlpdsp_init_arm.c | 3 +-
libavcodec/mlp.h | 10 +-
libavcodec/mlp_parse.c | 31 ++-
libavcodec/mlp_parse.h | 1 +
libavcodec/mlp_parser.c | 11 +-
libavcodec/mlpdec.c | 389
+++++++++++++++++++++++++++----
libavcodec/mlpdsp.c | 50 +++-
libavcodec/mlpdsp.h | 25 ++
libavcodec/x86/mlpdsp.asm | 19 +-
tests/fate/truehd.mak | 10 +
11 files changed, 476 insertions(+), 75 deletions(-)
With atmos.thd i get:
[aist#0:0/truehd @ 00000209caf3ee00] Guessed Channel Layout: 7.1.4
Input #0, truehd, from '../samples/truehd/atmos.thd':
Duration: N/A, start: 0.000000, bitrate: N/A
Stream #0:0: Audio: truehd (Dolby TrueHD + Dolby Atmos), 48000 Hz,
7.1.4, s32 (24 bit)
Which is unlikely to be correct. The file has 11 (or 12) objects, which
is exported as 12 channels in an unspecified layout, and automatically
assumed to be a 7.1.4 fixed layout.
This is caused by `guess_input_channel_layout` (in `ffmpeg_demux.c`) which
tries to assume a layout.
I wonder if the default value for guess_layout_max should be set to 8. An
unspecified layout with more than 8 channels seems unlikely. (unless it is
indeed unspecified/unknown)
Would using `AV_CHANNEL_ORDER_CUSTOM` with all channels set to
`AV_CHAN_UNKNOWN` (for unknown position, except LFE if present) be a
better solution?
AV_CHANNEL_ORDER_CUSTOM with all channels being AV_CHAN_UNKNOWN is
equvivalent to AV_CHANNEL_ORDER_UNSPEC. So unless there is a channel which
is not AV_CHAN_UNKNOWN, there is no reason to use AV_CHANNEL_ORDER_CUSTOM.
Regards,
Marton
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