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Full Version: No AC3 Passthrough for TrueHD in m2ts
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When trying to play some of my BD m2ts samples, I realized that KODI (Jarvis 16.1 and Krypton 17 Beta 1) only outputs PCM 2.0 via S/PDIF and HDMI-ARC for TrueHD tracks which have an AC3 stream included. What I wanted to achieve is that the AC3 stream is played via Passthrough. Is that somehow possible?

When playing a BD m2ts with DTS-HD MA, KODI happily detects the DTS core and sends it to the S/PDIF and HDMI-ARC via Passthrough. It just doesn't work for TrueHD with AC3 where I only get decoded PCM 2.0.

I am using KODI on my Sony KD-55XD8505 (X850D in the U.S.) TV running androidtv. The native media player of androidtv (called "Video") does AC3 Passthrough for TrueHD tracks inside m2ts.

Is this intentional, missing feature, a bad configuration on my side or a bug?
We don't have that implemented. Enable ac3 transcoding instead, as we can decode TrueHD just fine.
We once did it for the DVBSource filter (DVBViewer). It is actually quite easy to detect the AC3 frames in the TrueHD track. However I don't know what that means in the context of KODI. ffmpeg should be able to do it.

Thanks for your input.
While it's possible to have an interleaved TrueHD and AC3 track, I thought the vast majority of BD's had separate TrueHD and AC3 tracks, since interleaving them is not a requirement in the same way there is a DTS core plus extensions which then give DTS-HD.
I have lots of TrueHD m2ts samples (snippets from actual movies) and they all have interleaved AC3. I think it actually is a requirement, not by TrueHD in order to decode it (like it is the case with DTS-HD and its core), but per HDMV specs.
Here is what the BD specs say about it:
Quote:Dolby Lossless audio stream: A Dolby Lossless audio stream comprises two substreams; one
substream comprising a Dolby Digital audio stream and one substream comprising an MLP audio
stream. The Dolby Digital provides audio for replay on systems which cannot decode the MLP audio
stream.

Dolby Digital audio stream: One of two substreams of a Dolby Lossless audio stream. A Dolby
Digital audio stream consists of a sequence of Dolby Digital synchronization frames which can be
decoded by a Dolby Digital (AC-3) decoder. Dolby Digital audio streams are used to deliver up to 5.1
channels of audio. The Dolby Digital audio stream is decoded independently of the MLP audio stream
and a Dolby Digital decoder does not require access to the MLP audio stream.

I wonder how lower-end ARMs handle the transcoding. Does it add up some latency? So does it require adjusting lip-sync (audio offset)?
(2016-08-31, 10:15)jjd-uk Wrote: [ -> ]While it's possible to have an interleaved TrueHD and AC3 track, I thought the vast majority of BD's had separate TrueHD and AC3 tracks, since interleaving them is not a requirement in the same way there is a DTS core plus extensions which then give DTS-HD.

It's a requirement. But usually left out when downconverting to mkv as it takes up unneccesary space. With Kodi transcoding to AC3 makes this problem more of an academic art.

Note that the core of THD is not really a core, just interleaved with THD, but fully independent. Not like DTS where the DTSMA/DTSHD part is an extension of the core (even though it's possible to encode DTSMA without the core altogether).
(2016-08-31, 13:35)Soli Wrote: [ -> ]
(2016-08-31, 10:15)jjd-uk Wrote: [ -> ]While it's possible to have an interleaved TrueHD and AC3 track, I thought the vast majority of BD's had separate TrueHD and AC3 tracks, since interleaving them is not a requirement in the same way there is a DTS core plus extensions which then give DTS-HD.

It's a requirement. But usually left out when downconverting to mkv as it takes up unneccesary space. With Kodi transcoding to AC3 makes this problem more of an academic art.

Just to clarify what I meant since I posted in a rush, it was that my belief that it was not a Dolby requirement that all TrueHD tracks must also contain interleaved AC3, and also thought that since it wasn't a Dolby requirement many BD's used separate TrueHD and AC3 tracks. I'm sure I based this on something I read, but since I can't find or remember where perhaps I've not remembered correctly or the author was mistaken.


(2016-08-31, 13:35)Soli Wrote: [ -> ]Note that the core of THD is not really a core, just interleaved with THD, but fully independent. Not like DTS where the DTSMA/DTSHD part is an extension of the core (even though it's possible to encode DTSMA without the core altogether).

That's what I was trying to get at rather badly, that it's a fully independent AC3 stream and independent TrueHD stream interleaved.
Quote:and also thought that since it wasn't a Dolby requirement many BD's used separate TrueHD and AC3 tracks.
Most demuxers provide MLP and AC3 streams as separate tracks. That's probably why you thought there were two tracks while in reality there was only one interleaved track.

The KODI/ffmpeg demuxer seems to do just that. So it is actually possible to switch to the AC3 stream inside the TrueHD track via audio menu.
Maybe I got confused between BD & HDDVD

http://forum.doom9.org/showpost.php?p=14...stcount=13