No 5.1 audio on ac-3 mp4 file (2 chan out only). HDMI / Digital

Tried using latest Firmware as well as latest Beta Firmware. No 5.1 audio onto AV receiver using HDMI or Optical. Used the Digital setting under settings. Same file converted to mkv using mkvmerge has 5.1 audio (Same setup). Can someone help understand? Is Dolby Digital (AC-3 5.1) not supported on WD TV Live when used on mp4 files? (I used handbrake to create the mp4 - file from a DVD rip) 

Audio Stream Details
Format                           : AC-3
Format/Info                      : Audio Coding 3
Mode extension                   : CM (complete main)
Codec ID                         : ac-3
Duration                         : 2h 20mn
Bit rate mode                    : Constant
Bit rate                         : 384 Kbps
Channel(s)                       : 6 channels
Channel positions                : Front: L C R, Side: L R, LFE
Sampling rate                    : 48.0 KHz
Bit depth                        : 16 bits
Stream size                      : 385 MiB (25%)
Language                         : English
Encoded date                     : UTC 2010-10-25 03:04:34
Tagged date                      : UTC 2010-10-25 04:01:51

WD claims that AC-3 is supported within .mp4, in the manual for the Live/Live Plus.

I don’t have any .mp4 files at the minute, but that’s irrelevant as I don’t have an AVR either… I’d only get the stereo mixdown anyways even if I encoded a test file.

Somebody with a DD receiver will have to check this for you.

Actually, it’s even simpler than that – AC3 5.1 (and DTS 5.1) is not part of the MP4 standard (Apple TV has to jump through hoops to get this to work and even then it doesn’t always).

So the answer is, no, it’s not supported nor should it be.

mkelley wrote:

AC3 5.1 (and DTS 5.1) is not part of the MP4 standard

I’m not sure what you mean by that.

They’re both registered codecs for MPEG-4

The spec even has separate stream identifiers for the different flavours of DTS:

  • 0xA9 - DTS Coherent Acoustics audio
  • 0xAB - DTS-HD High Resolution Audio
  • 0xAC - DTS-HD Master Audio
  • 0xAD - DTS Express low bit rate audio, also known as DTS LBR

(ISO/IEC 14496-1, the MPEG-4 systems specification)

So why identify a DTS-HD track, if DTS is “not allowed”?

Likewise:

  • 0xA5 - AC-3 audio
  • 0xA6 - Enhanced AC-3 audio

Why provide identifiers for tracks that the format is “not allowed” to contain?

“Requests for a code-point in this area will normally also cause an objectTypeIndication to be allocated, so that the coding system can be used in MPEG-4 systems” seems to say they assign the identifiers for streams they expect to be used.

I get that “can be used” ≠ “must be supported by all systems”, but I see nothing at the Registration Authority that says you can’t have DTS or AC-3 5.1 in an .mp4 file… the authority has no control whether any .mp4 playback systems properly use the applicable standards to utilize a particlar stream, however.

No, it’s been this way (unsupported) ever since MP4/M4V ever came out.  Just go to the Apple forum (and THEY should know, as it’s their format) to find out the details.

See, I’m still confused by that.

I fully get that most are not supported by most .mp4 devices.

But the MPEG-4 Part 14 spec says that pretty much anything can be within an .mp4 file (but it’s up to the playback device/software to decide whether to support any private streams or not).

The MPEG-4 Part 12 spec says that the registered codecs can be within an .mp4 file (but again it’s up to the playback device/software to decide which registered streams to support).

The file specifications (both part 12 and part 14) say that you’re “allowed” to put DTS into an .mp4 file.

It doesn’t matter if nothing from Apple will currently play it back.  That’s Apple’s decision to make, to choose to not support the registered types and to not support private streams.

It doesn’t mean other playback software/devices are forbidden from playing back DTS or AC3 from an .mp4 file.

If the WD manual says that the WDTVs support AC3 in .mp4 then the WDTVs should support AC3 in an .mp4, whether Apple also wants to offer such support or not.

After all, the “Registration Authority” in charge of the registered codecs is run by Apple.  The Registration Authority sets the specs.  If both the specs and the RA says that DTS is valid, but Apple won’t support it, then they’re not even conforming to their own published specifications.

If AC3 is “forbidden” in the MPEG-4 files (which the specs say it isn’t), then why does Apple sell/rent .m4v files with 5.1 AC3 audio tracks?

I’d have to question where you found the specs.  On the Apple site?  If so, leave me the URL and I’ll take it up with the Apple people (I’ve been a Level 4 tech on their site for many many years now).

Trust me, this has been an issue with Apple users for a long time.  It’s also one of the main reasons not to use MP4/M4V as a container type (since it doesn’t support DTS either).

Honestly, I can’t find anything on the Apple site.  All they want to do is sell me things.  I’ve spent hours trying to search, and trying to click Google hits that point back to Apple, but I keep ending up in the iTunes store or some other ad selling something else of theirs, be it Quicktime Pro or an AppleTv or an iPhone.

The fact remains that DTS asked Apple to reserve the names of the streams, so that if someone comes along and wants to extract DTS tracks from an .mp4, the names won’t be being used by some other schmuck who wanted to call their stream “DTS.”  That in and of itself doesn’t signify any official “recognition” from Apple.  They’ve just processed the registration requests.  But they also could have said “No, nobody ever will be sticking tracks named ‘DTS’ in so there’s no need to reserve the names.”

The DTS entry listings are readily available from the mp4ra.org, along with all the other registered codecs and types.

AppleTV take 2 seems to support AC3 within .mp4, from what I’ve read elsewhere, and from the fact that Apple sells/rents .m4v files with AC3 5.1 audio in them.

I’m not about to pay the ISO’s prices to buy a copy of the specs, just to satisfy my own curiousity, but that would probably be worthless anyways, as it would describe MPEG-4 audio, not private stream audio within .mp4 containers.  The spec itself isn’t required to define all private streams that may be inserted.

The fact is that any player is required to ignore any private streams it doesn’t understand, from what I can read of the MPEG-4 Book.  Private streams can’t be “banned” from a specific container, per se.  Many players have been able to pull VOBSUB out of .mp4, as a private stream…  I believe Nero’s player has been pulling VOBSUB out of .mp4 for some time, despite subs not being nominally in the original MPEG-4 specs, because they fall under the “other” in the specs by being a private stream.

So, there’s no legal or technical reason why I can’t put AC3 or DTS into an .mp4 file, and there’s no legal or technical reason the WDTV can’t pull them back out.  That it doesn’t is another matter.  But it’s not that it “can’t”.  And whether Apple wants me and WD doing it or not is irrelevant.

I’d wager that the real reason WD isn’t pulling DTS out of .mp4 files has nothing to do with Apple saying it’s a no-no, and everything to do with the fact that nobody’s putting DTS into .mp4 files because nothing else will pull it out either.

WD TV to be a flexible device I think they should implement to passthrough the AC-3 to my receiver wheather it is mkv file or a mp4 file. My computer does that, and my DVD player does that and my PS3 does that. But not the WD. So it is wrong to assume that AC-3 is not in the spec of mp4 and there for should not be implemented. WD should implemented. I think WD also think about having a Menu setting for Passthrough Audio or Stereo Audio. What I get is Stereo Audio at the moment, and not pass-through. Implementing Pass-through audio should not be that hard using a firmware upgrade.

I do not believe, ac-3 should not be supported as an answer, it is a draw-back to the device, many other devices support it.

I’m not understanding the assumption that MP4 is an Apple thing.   It’s not.  

It’s an ISO standard (actually MANY, depending on which “Part” is being referenced.   

All sorts of people have patents pertaining to MP4.  

M4V *IS* an Apple extension.   If none of the proprietary extensions are present in an M4V (and with some of them, even if they ARE) they are fully MP4 compliant… 

TonyPh12345 wrote:

I’m not understanding the assumption that MP4 is an Apple thing.   It’s not.  

I get that MPEG.org is officially behind MPEG-4’s ISO standard.

But the .mp4 filetype is “maintained” by Apple, if I may word it that way.

To summarize:


This site is the registration authority for code-points in “MP4 Family” files. Within the documentation on this site are code-points from specifications both using and related to the ISO specifications for which this is the formal registry.

 

This site is run on behalf of the International Organization for Standardization, ISO, and supports in particular the working groups WG11 (MPEG) and WG01 (JPEG). However, a number of other organizations have specifications in the family.

Apple Computer operates this for the benefit of the standards community.


Apple running it on behalf of the ISO, makes it an “Apple thing” to me. :wink:

Wow. That’s a stretch.

:slight_smile:

Tony,

Apple “invented” MP4/M4V (they are *exactly* the same container – the only difference is in the name and while some devices prefer one name over the other there is no distinction internally).

What has happened since may have been it was co-opted by others, but all the more reason why additions to it would not be supported by Apple (and, by extension, other device makers).

Regardless, I’m pretty sure that’s exactly why the Live doesn’t support the 5.1 in it (but ask Guy or someone and they can give you the real scoop).  For the original poster it really doesn’t matter what the history is, only what can be done to get his files right (and I’m pretty sure the answer is not to use that container type).

I won’t stake my reputation on it, but I think y’all are misinformed… Mpeg 4 is NOT an Apple creation. MPEG 4 (part 14) is, but that is only one of several forms the WD supports. Part 2 was created by the Motion Picture Expert Group, and is probably far more common… The file extension is ambiguous, so gotta look deeper.

Tony,

Part 14 IS the movie format, and was directly based on the Apple Quicktime format.  I’m telling you, this is widely known by the Apple tech folks (I spent nearly a decade on the Apple support forum) and is their baby all the way. 

But, as I said, it really doesn’t matter.  What matters is whether the Live will support 5.1 in it, and since it’s not something Apple supports (very well, at least) I suspect that’s exactly why the Live treats it the same way.  But only Guy (or one of the other tech types) could tell us for sure.

If Guy says they purposefully did not support it then there’s not much the OP can do unless he wants to recontainerize (is there such a word?) or re-encode, as you and I well know WD ain’t gonna change things now.

AC3 is supported by many (dare I say most at this point) hardware and software players and tools that support mp4 files.  Its been part of the standard and in use for several years now (no matter if apple wants to support it on its devices or not, QT does support it).  Further, WD advertises they support ac3 in an mp4 container and then modify and downgrade the stream before outputting it rather than just passing it through to the digital outputs.  Makes no sense.  They read the stream and the intentionally modify it on the fly.  Its a programming bug, not a standards issue.

Did you know that Amazon VOD is using streamable mp4 with ac3 sound?  Its the ONLY stream format TivoHD units take natively for mpeg4 and ac3 and Tivo is notoriously behind the times on codec support.

Ac3 in an mp4 is also natively supported in Android 2.2

No, this is just a bug that WD has yet to address in thier software.  I have to admit, the HDMI issues they are currently STILL dealing with are higher priority.  And, no other hardware player box gets everything right either.

If Apple don’t support 5.1 in an mp4/m4v container, they should probably not be selling them via iTunes. All of Apples modern rentals / downloads have 5.1 Dolby Digital. I think RG mentioned that already.

That fact alone is sufficient evidence that the files exist, are supported by Apple, and should be supported by the Live range. It’s been an active Idea / suggestion since the launch of the original Live; WD just keep bumping other issues / fixes ahead of it.