Dolby TrueHD 7.1 downmix to 5.1 AAC

[justinhow]

When down mixing some Dolby TrueHD 7.1 soundtracks to AAC 5.1 the centre channel seems to get lost or moved (left). In practise the center soundtrack swings to the left channel on both a stereo system and a 5.1 system.
This does not appear to apply to all TrueHD soundtracks though.
I am using recent Nightly builds (various up to 2018010301 GUI) and also very recent nightly CLI (20180227)
Running on Windows Server 2016. Everything else works well and only found issue with TrueHD.
No errors are reported.
Before I start uploading logs etc is this a known issue?

Details of a problem soundtrack below however it is almost identical to one that works OK - 2nd listing below:

Code: Select all

<track type="Audio" typeorder="1">
<ID>2</ID>
<Format>TrueHD</Format>
<Format_profile>TrueHD+Atmos / TrueHD</Format_profile>
<Codec_ID>A_TRUEHD</Codec_ID>
<Duration>2 h 0 min</Duration>
<Bit_rate_mode>Variable</Bit_rate_mode>
<Bit_rate>5 693 kb/s</Bit_rate>
<Maximum_bit_rate>8 412 kb/s</Maximum_bit_rate>
<Channel_s_>Object Based / 8 channels</Channel_s_>
<Channel_positions>Object Based / Front: L C R, Side: L R, Back: L R, LFE</Channel_positions>
<Sampling_rate> / 48.0 kHz</Sampling_rate>
<Frame_rate>1 200.000 FPS (40 spf)</Frame_rate>
<Compression_mode>Lossless</Compression_mode>
<Stream_size>4.79 GiB (11%)</Stream_size>
<Title>Dolby Atmos/TrueHD Audio / 7.1-Atmos / 48 kHz / 5557 kbps / 24-bit</Title>
<Language>English</Language>
<Default>Yes</Default>
<Forced>No</Forced>
</track>

Code: Select all

<track type="Audio" typeorder="1">
<ID>2</ID>
<Format>TrueHD</Format>
<Format_profile>TrueHD+Atmos / TrueHD</Format_profile>
<Codec_ID>A_TRUEHD</Codec_ID>
<Duration>2 h 31 min</Duration>
<Bit_rate_mode>Variable</Bit_rate_mode>
<Bit_rate>3 941 kb/s</Bit_rate>
<Maximum_bit_rate>5 853 kb/s</Maximum_bit_rate>
<Channel_s_>Object Based / 8 channels</Channel_s_>
<Channel_positions>Object Based / Front: L C R, Side: L R, Back: L R, LFE</Channel_positions>
<Sampling_rate> / 48.0 kHz</Sampling_rate>
<Frame_rate>1 200.000 FPS (40 spf)</Frame_rate>
<Compression_mode>Lossless</Compression_mode>
<Stream_size>4.18 GiB (8%)</Stream_size>
<Title>Dolby Atmos/TrueHD Audio / 7.1-Atmos / 48 kHz / 4581 kbps / 24-bit</Title>
<Language>English</Language>
<Default>Yes</Default>
<Forced>No</Forced>
</track>

[Deleted User 11865]

When downmixing TrueHD, we use the embedded downmix whenever available (a.k.a. "6-channel presentation" in the Dolby encoder). My guess is that's where the issue comes from, though it's hard to be sure without access to the raw bitstream.

Which Blu-ray(s) are we talking about here?