Dolby AC-4 decoding support?

[hajj_3]

It seems as though vlc player and mpc-be do not support Dolby AC-4. From reading Dolby's own website (https://dolbyac4.com/uk/) it appears that U.K free-to-air satellite platform 'Freesat' has picked AC-4 as the exclusive next gen audio format for their 3rd generation satellite boxes that will be released this year. Therefore AC-4 broadcasts will likely happen this year not just a trial. It would be nice if FFmpeg/vlc/mpc-be added support to decode this audio codec. Does anyone know if work is being done in any of these to add support?

[hajj_3]

I found this, not sure if it will be helpful for us: https://github.com/DolbyLaboratories/dlb_mp4base

[filler56789]

I found this, not sure if it will be helpful for us: https://github.com/DolbyLaboratories/dlb_mp4base

Not helpful. That's an MP4 muxer, not an AC-4 decoder. This PDF file (https://www.etsi.org/deliver/etsi_ts/103100_103199/103190/01.01.01_60/ts_103190v010101p.pdf) might be useful, assuming there exist capable developers interested in transforming the specs into a functional decoder :-/

[nevcairiel]

Some work for FFmpeg to support AC-4 decoding has begun. When it'll be complete and/or usable .. we'll see.

[hajj_3]

Some work for FFmpeg to support AC-4 decoding has begun. When it'll be complete and/or usable .. we'll see.

nice :)

I can't seem to find any .AC4 sample audio files on the internet though which is annoying.

[nevcairiel]

If anyone has any AC-4 samples, that would be helpful for development. Preferably real-world samples, the commonly found ones in the DASH test suite etc, we already got. ;)

[nussman]

Some dvb broadcaster are sending ac4:
https://www.dvbviewer.tv/forum/topic/62027-dolby-ac4-sound-track/

I can ask for a sample if it helps.

[nevcairiel]

Already got some from the DVBViewer people, was hoping for more alternative samples to cover as much as possible, but thanks!

[hajj_3]

Already got some from the DVBViewer people, was hoping for more alternative samples to cover as much as possible, but thanks!

Please send all of your AC-4 samples to the developer of mediainfo, he wants some to add detection support: jerome@mediaarea.net

[hajj_3]

MediaInfo 19.09 changelog:

AC-4: basic detection, raw, in MP4 or TS

[FranceBB]

AC3 has been a good and reliable codec for ages but it needed an high enough bitrate, something like 320-384 kbit/s to sound really good and now there's AC4... How is it gonna be compared to AAC at no so high bitrates like 128-192 kbit/s, I wonder...
Well, I think we're about to find out in the near future.
Unfortunately, I do not have a sample since nobody ever sent us an AC4 audio file, otherwise I would have shared it...

[Atak_Snajpera]

AC3 has been a good and reliable codec for ages but it needed an high enough bitrate, something like 320-384 kbit/s to sound really good and now there's AC4... How is it gonna be compared to AAC at no so high bitrates like 128-192 kbit/s, I wonder...
Well, I think we're about to find out in the near future.
Unfortunately, I do not have a sample since nobody ever sent us an AC4 audio file, otherwise I would have shared it...

Most likely around opus levels... I doubt that ac4 will be better at very low bitrates.

[FranceBB]

Most likely around opus levels... I doubt that ac4 will be better at very low bitrates.

I see.
I never really bothered to monkey around with opus to be fair, but that's only 'cause opus was born as a low-bitrate speech-optimized codec which has been extended to support other profiles for general contents encoding and because of that, its adoption has never been very widespread for general purpose contents and therefore many devices don't officially support it. For this very reason, I've been using AAC to encode audio files in lossy. It's pretty much the same reason why, whenever I gotta keep an audio file lossless, I still keep the original PCM in .wav instead of re-encoding it to FLAC: the megabytes it saves are negligible compared to the fact that almost nothing will play it.

[SeeMoreDigital]

AC3 has been a good and reliable codec for ages but it needed an high enough bitrate, something like 320-384 kbit/s to sound really good and now there's AC4... How is it gonna be compared to AAC at no so high bitrates like 128-192 kbit/s...If I had to guess, I reckon it's more likely that AC4 coding technology is derived from E-AC-3, which works much more efficiently at lower bit-rates than AC-3...

From Dolby's blog [2017]: Hearing Is Believing: Comparing Dolby AC-4 to Dolby AC-3 (https://blog.dolby.com/hearing-is-believing-comparing-dolby-ac-4-to-dolby-ac-3/)

[Atak_Snajpera]

I see.
I never really bothered to monkey around with opus to be fair, but that's only 'cause opus was born as a low-bitrate speech-optimized codec which has been extended to support other profiles for general contents encoding and because of that, its adoption has never been very widespread for general purpose contents and therefore many devices don't officially support it. For this very reason, I've been using AAC to encode audio files in lossy. It's pretty much the same reason why, whenever I gotta keep an audio file lossless, I still keep the original PCM in .wav instead of re-encoding it to FLAC: the megabytes it saves are negligible compared to the fact that almost nothing will play it.

Opus is a standard audio codec on YouTube so every android device (Smart TV/smartphone) must support IT.

[SeeMoreDigital]

... I still keep the original PCM in .wav instead of re-encoding it to FLAC: the megabytes it saves are negligible compared to the fact that almost nothing will play it.Eh???

I would hardly call an average 50% reduction in a Flac file size over PCM file size "negligible"...

Also in my case... my OPPO's, my Onkyo AVR, my Android mobile phone, my Android tablet and my LG televisions (via HDD) can play Flac files.

[hajj_3]

Some work for FFmpeg to support AC-4 decoding has begun. When it'll be complete and/or usable .. we'll see.

Do you have a link to this development as i can't find anything about ffmpeg adding support?

[richardpl]

I have link, but I will not share it, as you probably do not know, nothing comes on this world for free.

[FranceBB]

I have link, but I will not share it, as you probably do not know, nothing comes on this world for free.

What? Isn't ffmpeg supposed to be free, open source and available to everybody?

Do you have a link to this development as i can't find anything about ffmpeg adding support?

Those are the only commits I was able to find and they're from February 2019:

add AC-4 codec id and description:
http://ffmpeg.org/pipermail/ffmpeg-devel/2019-February/240221.html

add mapping for AC-4 in MP4:
http://ffmpeg.org/pipermail/ffmpeg-devel/2019-February/240222.html

Both from Paul B Mahol.


I also found a ticket, namely #8349 where Nomis101 (https://trac.ffmpeg.org/query?status=!closed&reporter=Nomis101) asked about Decoding Support of AC4 in ffmpeg. At the very beginning they marked it as closed three months ago, but then richardpl re-opened it and it's currently opened and set to "wish".

@richardpl are you one of the developers behind ffmpeg?

[richardpl]

What? Isn't ffmpeg supposed to be free, open source and available to everybody?

Whatever. There is no free lunch.

[microchip8]

Whatever. There is no free lunch.

Why are you being such a dick? Are you planning to charge for it?

[richardpl]

Why are you being such a dick? Are you planning to charge for it?

I just want some money for my time spent on it.

[RealSnoopyDog]

And it seems as if Dolby also wants money:

https://blog.dolby.com/setting-record-straight-dolby-ac4-mpegh/

[nevcairiel]

Dolby always wants money, for AC-3 and AC-4 alike, as does everyone else, software like FFmpeg leaves patent licensing up to the users however, otherwise very little would ever be implemented.

[littleD]

So, how do You explain that commit, a contribution from Dolby labolatories https://github.com/google/ExoPlayer/pull/5303/files

[richardpl]

That commit alone will not give you decoding support for AC-4 files.

[Andouille]

That commit alone will not give you decoding support for AC-4 files.

We just have to wait and uncompetent greedy people will be screwed with their scam .hr

[Blue_MiSfit]

Yeah looks like that's basically demuxer support, maybe handing off to an AC4 decoder in the SOC.

Also, come on now! Companies have to make money otherwise they can't pay their engineers. It's easy to hate on Dolby for being litigious, but they've moved the industry forward a lot over the last few decades. That has to be a factor!

[SeeMoreDigital]

Over a year has gone by since this topic was started.

Does anybody have some AC4 sample files?

[littleD]

Yeah, it looks like demuxer providing stream for "hardware" decoder or other decoder based on Android decoding framework.

I also read comment on github that this commit "might" have bundled AC-4 decoder, but it could be me who read wrongly, or other person made mistake commenting this github commit. I cant read the code.

Anyway, some smartphones show to have ac-4 decoder. Who would provide this. Phone vendor or android? This info is quite old https://www.prosoundnetwork.com/post-and-broadcast/ac-4-audio-delivery-picks-up-pace

AC-4 test file is included in the above commit we talk.

[hajj_3]

MediaInfo 20.03 changelog:

AC-4 full featured support (presentations, groups, substreams)
MPEG-H 3D Audio basic support

[richardpl]

MediaInfo 20.03 changelog:

AC-4 full featured support (presentations, groups, substreams)
MPEG-H 3D Audio basic support

Very useful information!

[SeeMoreDigital]

AC-4 test file is included in the above commit we talk.I must be blind... I can't find this test file!

[soresu]

I must be blind... I can't find this test file!

I think the sample is this file?

Link (https://github.com/google/ExoPlayer/blob/release-v2/library/core/src/test/assets/ts/sample.ac4).

[SeeMoreDigital]

I think the sample is this file?

Link (https://github.com/google/ExoPlayer/blob/release-v2/library/core/src/test/assets/ts/sample.ac4).
Yes... Unfortunately that particular sample dates back to January 2019.

Is there really nothing else?

[SeeMoreDigital]

MediaInfo 20.03 changelog:

AC-4 full featured support (presentations, groups, substreams)
MPEG-H 3D Audio basic supportIndeed... Look at what it reveals about this Jan 2019 (https://github.com/google/ExoPlayer/raw/release-v2/library/core/src/test/assets/ts/sample.ac4) sample: -

General
Complete name : d:\SeeMoreDigital\Downloads\sample.ac4
Format : AC-4
Format/Info : Audio Coding 4
File size : 7.42 KiB

Audio
Format : AC-4
Format/Info : Audio Coding 4
Commercial name : Dolby AC-4
Format version : Version 2
Sampling rate : 48.0 kHz
Frame rate : 25.000 FPS (1920 SPF)
Compression mode : Lossy
Number of presentations : 1
Number of substreams : 1
Presentation #1 : Immersive Stereo Main (English)
Presentation ID : 0
Dialogue normalization : -23.00
Language : English
Loudness : Yes
Integrated loudness (level gated) : -22.5 LKFS
Audio Loudness Standard : ATSC A/85
Realtime loudness corrected : Yes
Dialogue corrected : No
Dynamic Range Control : Yes
E-AC-3 DRC profile : Film standard
Home theater AVR : Film light
Flat panel TV : Film standard
Portable speakers : Film standard
Portable headphones : Film standard
Group #s : 1
Group #1 : Main
Content classifier : Main
Language : English
Channel coded : Yes
Immersive stereo : Multichannel Content
Number of substreams : 1
Substream #s : 1
Substream #1 : Stereo
Channel mode : Stereo
Immersive stereo : Multichannel Content
Channel layout : L R
Dialogue enhancement : Yes
Enabled : Yes
Max gain : 9 dB

[hajj_3]

It looks as though gstreamer might have added support possibly: https://gstreamer.freedesktop.org/releases/1.18/

There are quite a few ATSC 3.0 tv channels available in america now that use dolby ac-4 btw.

[SeeMoreDigital]

There are quite a few ATSC 3.0 tv channels available in america now that use dolby ac-4 btw.Excellent news... Any test samples yet?

[hajj_3]

Excellent news... Any test samples yet?

You could try asking owners of of capture devices on reddit to record some samples for you: https://www.reddit.com/r/PleX/comments/jf1zym/hdhomerun_connect_4k_preorder_available/

[clsid]

Development of an open source decoder requires sample files for testing. If anyone has samples, then post them on the FFmpeg bug tracker here:
http://trac.ffmpeg.org/ticket/8349

If a recorded ATSC stream is too large for upload, then you can use DGSplit (http://rationalqm.us/dgsplit/dgsplit12.zip) to make a small binary cut from front of file.

Once FFmpeg has decoding capability, it automatically flows down to many other projects that depend on it, including MPC-HC and VLC.

[Reino]

@richardpl are you one of the developers behind ffmpeg?richardpl = Paul B Mahol.

[hajj_3]

It looks as though AC-4 decoding is working now in ffmpeg builds: https://trac.ffmpeg.org/ticket/8349

Very cool, can't wait for a stable version of FFmpeg to be released supporting it.

[FranceBB]

It looks as though AC-4 decoding is working now in ffmpeg builds: https://trac.ffmpeg.org/ticket/8349

Very cool

That's so cool, considering that the alternative would be buying a super expensive Dolby DP580!!
Well done, everybody! :D

[speedy]

Does anyone know of a static build that can be downloaded with AC-4 support?

[richardpl]

Sharing such binary would break Dolby IP rules and is big legal offence.

[kurkosdr]

AC3 has been a good and reliable codec for ages but it needed an high enough bitrate, something like 320-384 kbit/s to sound really good and now there's AC4... How is it gonna be compared to AAC at no so high bitrates like 128-192 kbit/s, I wonder...

The big sell of AC4 is that it can separate dialogue from music and effects, so you can have multiple (https://www.digitalbitrate.com/dtv.php?mux=HEVC&pid=300&live=1&sec=0&lang=en) "dialogue" groups for the different languages sharing one "music and effects" group (and the AC4 decoder can mix the chosen "dialogue" group with the "music and effects" group to give the final output), which is where the big bitrate savings come from. There are countries in the EU which are bilingual or even trilingual, so even when using efficient audio formats giving 96Kbps per stream, you are still looking at ~0.3Mbps just for audio.

One remaining question is if AC4 supports full (albeit lossy) Atmos (aka how many ceiling channels it supports). Haven't found a clear answer to that so far.

[kurkosdr]

Sharing such binary would break Dolby IP rules and is big legal offence.
Which brings up that other important question: Since AC4 is an essential format for watching HEVC free-to-air terrestrial broadcasts in some countries, do we have a patent list?

[clsid]

What different compared to other patented codecs?
Software patents are meaningless in for example France, so why could VLC not use it in a binary?

[kurkosdr]

What different compared to other patented codecs?
Software patents are meaningless in for example France, so why could VLC not use it in a binary?
VideoLAN (VLC), which is based in France, can do that, websites based in the US (or other countries enforcing software patents) can't.