[FFmpeg-trac] #8349(undetermined:open): Dolby AC-4 Support

[FFmpeg]

#8349: Dolby AC-4 Support
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             Reporter:  Nomis101     |                    Owner:  (none)
                 Type:  enhancement  |                   Status:  open
             Priority:  wish         |                Component:
                                     |  undetermined
              Version:  git-master   |               Resolution:
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by skyler):

 What I would like to know is whether there is a static build of ffmpeg
 similar to John VanSickle's build at https://johnvansickle.com/ffmpeg/
 that include the AC4 support.

 In case anyone wonders why people are wanting this, I refer you to the
 thread at
 https://forum.silicondust.com/forum/viewtopic.php?t=77067&sid=0446c9341c1db6d3f24a2db24a5dd059
 which in a series of posts pretty much explains the current situation.
 But the short version is that if you purchase a HDHomeRun tuner capable of
 receiving ATSC3 signals, by default you probably won't get a usable audio
 signal unless all your equipment is very new (basically it must have Dolby
 Atmos support, as I understand it).  This also means you don't get audio
 on things like computer desktop systems or HTPC's, since none of them that
 I'm aware of have AC4 audio support.

 Silicon Dust's current solution is to have their devices send the AC4
 audio to a cloud server where the audio is turned around and sent back to
 the device as a two channel STEREO stream.  So instead of getting 5.1
 audio as is usual with current ATSC1, you get 1970's era stereo.  And
 there are other disadvantages as well - if you lose your internet
 connection or it gets very congested (as might happen when hundreds of
 users are all sending streams to be decoded during prime time), you would
 lose the audio and possibly would not be able to view or record live TV.
 If you record a show using backend software (Tvheadend, MythTV, etc.) you
 will either record the AC4 audio (which still can't be played on most
 devices) or the stereo from the cloud server, depending I suppose on how
 you have configured the HDHomeRun device.  And also, for those who care
 about such things, it gives Silicon Dust a way to track what you are
 watching (which is a big NOPE as far as I'm concerned, although some
 people don't seem to care if their viewing habits are tracked).

 A version of ffmpeg with AC4 support, on the other hand, should be able to
 convert the AC4 audio to AC3 or AAC or even MP2, whatever would be
 compatible with a user's receiver or computer or HTPC in almost real time,
 or on a previously recorded program if that is desired. And this would not
 be in any way dependent on Silicon Dust's servers, nor would it limit you
 to only two audio channels.

 I might have purchased a new HDHomeRun device with ATSC3 support almost a
 year ago, when stations in my area first started offering ATSC3
 programming, if it weren't for the stupid way they are handling the audio.
 Now, I think the U.S. FCC made a big mistake by allowing the use of AC4 in
 the first place, but that's another discussion for another forum. In the
 meantime, it would be really helpful if support for AC4 decoding could be
 included in either the main ffmpeg distribution, or failing that, in a
 static build that will run on Linux systems so it can be used with server-
 based backends like Tvheadend or MythTV or similar software (similar to
 the John Van Sickle build).  Really, I would think that only AC4 decoding
 is needed at the present time; I can't think of a single situation where
 anyone would want to encode using AC4 and would not already have access to
 a hardware-based encoder.

 I know some of you guys are conversant enough in Linux to be able to build
 your own custom builds of ffmpeg and that is great, but I haven't the
 foggiest idea how to do something like that and unless someone publishes
 "cookbook" type instructions (or better yet, a video walkthough of how to
 do it) on a Linux system, that will probably forever be beyond my skill
 set.  That's why I would really like to see this in the main ffmpeg
 distribution, or at least in a separate static build at some point in the
 not too distant future.  Right now all ATSC3 signals are still available
 as ATSC1 (though not always with the exact same coverage areas) but that
 will not be the case forever.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/8349#comment:59>
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