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LPCM sorely needed

Posted: Sat Nov 09, 2019 4:19 am
by markfilipak
Description of problem or question: LPCM is not encoded, nor will it pass through. Therefore, audio doesn't work in homemade home theater system.

HandBrake version (e.g., 1.0.0): 1.2.2 (2019022300)

Operating system and version (e.g., Ubuntu 16.04 LTS, macOS 10.13 High Sierra, Windows 10 Creators Update): Win10-1803
BradleyS wrote: Mon Aug 05, 2019 9:08 am LPCM is something I hope we can add soon.
I'm making MKVs and I think MKV supports LPCM. This is important because I have a homemade home theater that employs a downstream HDMI Audio Extractor with 6 RCA jacks to feed 2, 4-channel amps. The Extractor only decodes LPCM audio. Since HB currently can't encode LPCM, playing an MKV results in FL + FR only (via the TV's speakers). Since there's no C channel on the TV, actors in the center-front make no sounds at all. Also, movies that contain 5.1 (or 7.1) LPCM don't pass through because HB replaces the LPCM with AC3 (which the Extractor can't decode).

Regards,
Mark.

Re: LPCM sorely needed

Posted: Sat Nov 09, 2019 3:57 pm
by Woodstock
LPCM pass through is on the enhancements list, but there is no timetable for it. It's an open github request going back two years.

Re: LPCM sorely needed

Posted: Sat Nov 09, 2019 4:05 pm
by musicvid
Sounds like you are looking for a custom fix for your unique system. But you've already identified your best solution, for now.
I'm making MKVs and I think MKV supports LPCM.
Yes, there are any number of muxers, which Handbrake is not, that will do this.
MakeMKV, MKVToolnix, ffmpeg, mp4Box, AVIDemux, just to scratch the surface.
Discrete LPCM multichannel is not a conventional delivery format, except for a few BD / DVD formats, which again Handbrake does not author.
It is quite large and inefficient, as I'm sure you already know, maybe 4x larger than mainstream audio delivery formats.

Most important, Handbrake MKV is just wrapped from a normal mp4 encode. in which LPCM is allowed, but not widely incorporated or supported by conventional home media systems and players. That said, yes, passthrough would be a worthy feature for some users.

Re: LPCM sorely needed

Posted: Sat Nov 09, 2019 5:54 pm
by markfilipak
There's a lot of people whose old, premium audio gear doesn't take HDMI. There's close to a dozen companies making HDMI audio extractors to feed that old gear. They probably all use the same chip. They all seem to work with LPCM only. Users are buying them and returning them. Sad.

Re: LPCM sorely needed

Posted: Sat Nov 09, 2019 6:09 pm
by Ritsuka
Try FLAC. It will be decoded to lpcm by the player so it should work (if your player supports it). It's possible to decode AC-3 to lpcm too, it all depends on your player settings.

Re: LPCM sorely needed

Posted: Sat Nov 09, 2019 7:44 pm
by musicvid
Yes, the devil is in the players, and of course their age.
Also, I used to be able to hear a difference with chop-top lossy encoders, such as ac3, aac, and mp3.
Now I can't really tell a difference, except my tolerance for quantization artifacts and harmonic distortion has gotten worse, especially the way they mix audio for broadcast these days. Abominable.

Re: LPCM sorely needed

Posted: Sat Nov 09, 2019 9:41 pm
by Rodeo
If you encode to FLAC, then you can re-decode to LPCM with third-party tools after the HandBrake encode, if necessary.

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 9:40 am
by BradleyS
I would also like to see PCM support added, if only to better suit the Production presets. I use PCM quite a lot as well, typically over SPDIF, the optical implementation not supporting many channels. I still find it a shame MP4 does not officially support PCM audio, hacks in the wild notwithstanding.

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 1:52 pm
by musicvid
Actually, the spec supports it, we would love to see it, but it's rarely spotted in the wild; just a few hobbyists, and almost no media center or DLNA support for PCM. I played around with it when I was producing live musicals. Ever tried to sync that stuff? Only seemed to work for me with true AVCHD, not MP4-PS.

My only advice for audiophiles is, "Burn a BluRay."

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 7:43 pm
by BradleyS
LPCM is not part of any official version of the MPEG-4 Part 14 specification.

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 10:01 pm
by musicvid
Not that it matters, a red herring is still a red herring. As of July, 2019, it appears to be supported by MP4RA, unless wiki is wrong.
https://en.wikipedia.org/wiki/Compariso ... ts_support

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 10:06 pm
by BradleyS
Yep, oddly enough when I loaded https://mp4ra.org/#/codecs on mobile and searched for pcm to double check before posting, it did not hit. But of course it is there now on desktop. I stand corrected. Naturally, many (most?) common devices don't support it, sadly.

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 10:15 pm
by musicvid
I checked deeper on MP4RA, and found it under the mp42 QT specification.
Naturally, many (most?) common devices don't support it, sadly.
And that's really all that counts on the street -- if the $$ don't support it, no one will.
OTOH, there are mutant formats (x264vfw / mp3 twice-hacked) that can never be officially supported, but are wildly popular, for reasons still unbeknownst to me.

So yeah, it comes down to the old hobbyist/production debate, which I've already unfortunately drummed to death on this forum.

Passthrough, sure. I'll use it, I just won't try to deliver it past my front door. I imagine a lot of problems with sync, though.

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 10:36 pm
by musicvid
So who is the "official" registrar?
MP4RA or MPEG4-LA ?

Re: LPCM sorely needed

Posted: Sun Nov 10, 2019 10:45 pm
by BradleyS
AFAICT it's still not in the actual ISO spec per se. MP4RA is so vendors can communicate their identifiers to avoid stepping on each others' toes. Both are relatively official, each in their own sense. LA mostly deals with licensing.

Re: LPCM sorely needed

Posted: Mon Nov 11, 2019 2:57 am
by musicvid
Of course, licensure. Silly question.

Re: LPCM sorely needed

Posted: Mon Nov 11, 2019 8:42 pm
by Rodeo
The RA has no LPCM code points for MP4 that I know of, only MOV. But then there's always MKV.