大象传媒

On a related topic: why are programmes with DD2.0 soundtracks now are all being flagged as DD5.1 on 大象传媒 HD on Freesat? Most annoying as you need to keep checking and adjusting how the AV amp processes the audio for best results.

It's a shame early adopters are the ones loosing out here. Especially when the freeview website makes completely false claims about Freeview HD's Surround Sound ability for existing surround sound equipment.

This comment was removed because the moderators found it broke the house rules. Explain.

Thanks very much for this explanation; just what I've been hoping for.

That April 2011 date is good to have, and it's a great shame (put mildly) that transcoding wasn't mandatory from the start.

It also raises another question: next spring, there will be kit on sale that has the Freeview HD that was launched before April, and won't transcode, and kit that was launched after April, and will. Obviously, it'll be vitally important for consumers to know which will work with their existing AV systems, and which won't. And I'd love to know how exactly they're supposed to find out.

Of course, that's more the province of Freeview than the 大象传媒, or the DTG, who operate the testing/certification scheme.

I totally agree with Liam. Many people have spent hundreds of pounds on thier AV amplifiers. The 大象传媒 could be accused of misselling in this case and many will be very anoyed at being sold incompatable kit. It fact I suspect under the sale of goods act they could ask for thier money back as the HD boxes are unfit for purpose.

When I first read that the 大象传媒 was to use AAC I was a bit puzzeled. Of cource AAC is a very good codec but it is incompatable with all the AV amplifiers I know about. Phils solution of providing LCPM on the HDMI link is good but many of the cheaper amps do not have HDMI inputs. Transcoding to dolby is not a good idea because it will introduce a loss of quality. The simplest solution is to mandate that all HD boxes have a 6 phono output sockets. It is quite clear that anyone interested in surround sound should steer clear of Freeview HD.

The 大象传媒's introduction of HD has been a total fiasco. First of all they chose to have a seperate HD channel with all the inherant scheduling problems. They then drop the bitrates to give us the poorest quality pictures on UK HD. There has been numerous problems with delivering surround sound. Many of these problems arrise from trying to deliver HD with an inadequate bitrate allocation. This is a real problem with Freeview HD as even with DVB T2 there is much less bandwidth per multiplex than on satelite. To provide a good quality service on Freeview would require the use of only 2 or 3 channels per multiplex.

I really don't think the 大象传媒 have missold stuff; they've gone for a technical solution that, actually, is quite sensible and elegant, without the issues around legacy compatibility that affect Freesat.

But it seems to me that manufacturers have had too much leeway, allowing them to get exemptions and sunrise periods in the specs, resulting in equipment not supporting everything from the start. And Freeview - not the 大象传媒 - have compounded that by not making it clearer on their website that, if you want surround sound, you really do need too check very carefully what kit you're buying.

Transcoding to Dolby Digital (or DTS, which is also allowable) will of course introduce a small loss of quality, but frankly I doubt that most people will notice it, and it is important, because an S/PDIF connection is very likely the most common way of connecting up surround equipment in the majority of domestic installations right now. People are far more likely to have equipment that can accept optical or co-axial S/PDIF than they are to have equipment with a six channel analogue input.

(And personally, I think the separate HD channel is a much more sensible idea than simply upscaling loads of SD content from a single one, but that's really off-topic for this discussion I'd have thought)

This isn't the place to do it but unofficially I will say that Humax has recognised this issue and has committed to improving the support for HD sound on the latest Freeview HD boxes in line with the latest revision of the specification.

Writing specifications is often as difficult as implementing them and sometimes the process can take some time to get true clarification. The DTG which specifies these things is composed of a mixture of broadcasters, service providers and in particular experts from the manufacturers. The next generation of HD PVRs from Humax will support this from launch and the existing HD simple set-top boxes should have an update to improve this in due course.

On the subject of sunrise clauses, they are there because the standards process for a technology is likely be completed while some product is being developed. If no-sunrise dates were given a manufacturer would be playing a continuous game of catch-up trying to ensure that a product was compliant to a specification that was only agreed the week before it was to be tested. In general a manufacturer will attempt to be responsible in their design as well as innovative to keep ahead of the competition and also a broadcaster will generally only promote a service when sufficient product is available to support the technology. In this case there was a disconnect and differing opinions about how to interpret the specifications which confused matters. It is rare for such occurrences to happen and I am sure other manufacturers will be as responsible as Humax in ensuring these issues are cleared up as soon as practicable.

Bob @ Humax

You say"

"Some 大象传媒 HD programmes, including The No.1 Ladies' Detective Agency and Robin Hood, are available in digital surround sound if you have the right equipment, i.e. a multichannel surround sound or home cinema system."
/reception/digitaltv/faq_hd.shtml

Now you are saying that almost no surround equipment on the market will be able to receive surround sound as surround amplifiers normally decode AC-3 or DTS but not AAC.

We bought equipment as per your above and much earlier description and now you are telling us that we won't be able to receive surround!

Well done 大象传媒 - NOT!!!

This is called missleading the public at best and lyeing to the public more likely.

To be fair, that page has just been slightly tweaked since the launch of Freeview HD, and probably not by someone who knows all the technical ins and outs. The vast majority of people watching 大象传媒 HD at the moment aren't watching it on Freeview, and so don't face this particular issue. It does not affect platforms like Freesat, Sky or Virgin.

Hopefully, thanks to this blog, those who are using Freeview will ask more questions before they buy.

@Nigel Whitfield

This is not a question of legacy compatability. As far as I amware there are no AV amplifiers or Televisions which support AAC on the market. This means that it is not possible for anyone to receive Surround Sound on Freeview HD. The DTG should have been aware of this. For instance Blu-ray supports a wide range of audio formats. In order to support this many Blu-Ray players output LPCM though HDMI and may also have 6 channel analogue output. In other words the issue was well known in the industry and the DTG was incompetent in not addressing it from the start.

As for transcoding from AAC to Dolby I am not sure as I have not seen any listening tests for this. It is well known that transcoding between different codecs can cause some very undesirable effects. With suuround sound the problems may be exasperated by spacial as well as phase effects.

All these issues are caused by the 大象传媒 trying to deliver an HD system on the cheap. The problem is that if you make it too cheap the quality deteriates to a level which makes the whole exersize pointless. The whole esence of HD is High Quality pictures and sound.

If that is the tweaked page, I cannot imagine what is the non-tweaked version? What it says 'now' is missleading at best. How was it before, blatantly lying?

It says all you need is "a multichannel surround sound or home cinema system". You have very eloquently proved that not to be the case. Almost no surround decoder on the market can decode what 大象传媒 is broadcasting from day one. They knew this to be the case but they didn't tell it to the license payer. Call it laziness, calculating, whatever, it is a fact that they hide the information till today's blog post.

Since 大象传媒 HD transmission has started (after the London only beta) public had no idea that they cannot hear surround sound *when* it is broadcasted. What is the point of feeding that information to the media (like DigiGuide) if the public is unable to benefit from it?

trevorjharris wrote:

"[...] there are no AV amplifiers or Televisions which support AAC on the market. This means that it is not possible for anyone to receive Surround Sound on Freeview HD."

This is exactly my point. If the FreviewHD logo is not defining the suitability of the receiver than what is the point of having the logo?

THE sole purpose of the logo is to give consumer the guidance that the unit he is buying is suitable for the job. In 大象传媒's case it surely is not!

Same happened with HD Ready. They have placed HD Ready logo on Plasma TVs with 1024 pixel by 1024 pixel panels. Joe Public who bought such a "HD Ready" display would had been asking why there was no visible difference when he tuned to a HD channel or plugged in a BR player?

The previous version of the page, presumably, didn't mention Freeview HD, because it wasn't operating. And if you were to omit all mention of Freeview HD from that page, then it would be absolutely correct. That is why I suspect it's merely been tweaked, since the launch of Freeview HD, and probably by someone not 100% au fait with the situation. So, to characterise it as deliberately misleading, or lying, is a little over the top I feel.

I know this is an important issue - after all, I've been blogging about it for weeks now, and pushing hard to raise its profile. But blaming everything on the 大象传媒, and suggesting they're deliberately misleading people isn't actually helpful.

There is kit out there that can produce surround sound from Freeview HD, just not very much of it. I know that, because I have some of it in my living room right now.

The real fault, it would seem to me, is not with the 大象传媒 for trying to do something on the cheap - I don't quite see how using AAC rather than Dolby is necessarily a cheap solution - but with the DTG and Freeview, who between them oversee certification, and have simply told people that you get surround with Freeview HD, without any qualification.

It is those parties, surely, who have a more pressing need to answer questions than the 大象传媒 engineering team.

"Freeview is managed by DTV Services Ltd, a company owned and run by its five shareholders - 大象传媒, BSkyB, Channel 4, ITV and Arqiva."


Nigel Whitfield wrote:

鈥淸...] I suspect it's merely been tweaked, since the launch of Freeview HD, and probably by someone not 100% au fait with the situation. So, to characterise it as deliberately misleading, or lying, is a little over the top I feel.

鈥淸...] blaming everything on the 大象传媒, and suggesting they're deliberately misleading people isn't actually helpful.

鈥淭he real fault, it would seem to me, is [...] with the DTG and Freeview, who between them oversee certification, and have simply told people that you get surround with Freeview HD, without any qualification.

鈥淚t is those parties, surely, who have a more pressing need to answer questions than the 大象传媒 engineering team.鈥�

Nigel, 大象传媒 is a single entity. I pay my license fee to one 大象传媒. I am writing on topic at a '大象传媒' website. You cannot split engineering from the rest of the corporation. 大象传媒 is co-founder and partner of Freeview. They are in the committe(s) who decide how the Freeview logo will be used. They knew from the beginning what the Freeview HD logo meant. If they objected they could do that -- publicly!

I blame all to 大象传媒 because they have a remit to work for me -- the Joe Public! If they fail, I blame them of not doing their job right. If they fail to guide me, or -- as in this case -- miss-guide me then I shout. The other partners are commercial entities. If I don鈥檛 like what they do I don鈥檛 buy their services. They do not have a remit to serve me. 大象传媒 has.

Wikipedia defines lying as "A lie (also called prevarication, falsehood) is a known untruth expressed as truth. A lie is a type of deception in the form of an untruthful statement..."

English is not my mother tongue so correct me if I am wrong, but what 大象传媒 did -- and still does on the referred page -- can only be defined as lying.

Nigel Whitfield wrote:

"There is kit out there that can produce surround sound from Freeview HD, just not very much of it. I know that, because I have some of it in my living room right now."

Forgot to add this: From what I read in your blog, you have a certain combination of kit that works. You cannot buy 'a' Freeview HD decoder which has the logo and plug it to 'a' SOTA surround amplifier and expect it to work 100% of the time. Correct me if I am wrong.

If I am correct than my point is valid: the logo is meaningless and it is a deception=lie.

To Bob @ Humax said:

"On the subject of sunrise clauses, they are there because the standards process for a technology is likely be completed while some product is being developed. If no-sunrise dates were given a manufacturer would be playing a continuous game of catch-up trying to ensure that a product was compliant to a specification that was only agreed the week before it was to be tested."

You would have been correct if:

a- The Freeview HD logo had the words 'draft' or 'beta' attached to it (like in Draft-n Wi-Fi standard) or,

b- Freeview hadn't spend a year to beta test the service for more than a year.

Hence they don't have a leg to stand on. If this had effected a large portion of the public it would invoke an OFCOM investication.

So is Freeview HD currently broadcasting 5 or 6 channel AAC? Otherwise, I'm somewhat confused how 'transcoding' to a surround sound codec will magically add the surround channels.

Also, I'm not aware of how developed AAC is for >2 channel encoding, but is it really as efficient for 5/6 channels as AC3 or DTS? Decoder technicalities aside, why not just broadcast in AC3/DTS and use a compatible codec for the audio description (encode it as an alternative channel in the AC3/DTS, if that's possible)?

Another issue I see: the cost of receivers will rise due to AC3/DTS encoder licensing costs if the transcoding requirement is met. Though I admit, I don't know how much this will be (and it's probably quite small).

In an ideal world though, I applaud the DTG's engineers for this very elegant solution. It's just a shame consumer device support is so poor.

Gomex first post about DD2.0 soundtracks now are all being flagged as DD5.1 on 大象传媒 HD on Freesat seems also to affect the Freeview HD service.

I have a new Panasonic DMR-BW780 and notice that my Sony STR-DA2400ES surround amplifier always indicates 5.1 even when the broadcast is only DD2.0!

This also confirms that the latest kit outputs the HE-AAC as multichannel bitstream LPCM.

Now I just need the 大象传媒 to correctly flag the audio!

The AAC soundtrack, for programmes with surround, is 5.1. And you can convert that from AAC 5.1 surround to Dolby Digital 5.1 surround, just as you can convert from, say, AAC stereo to MP3 stereo. All you're changing is the codec. Though, of course, relatively few programmes are in 5.1 at the moment.

AAC (and in particular HE-AAC) can produce better quality than AC3 at lower bitrates, though at the moment, it's not the bitrate that's the issue of course. Even some papers from Dolby acknowledge the better performance of HE-AAC for surround when bandwidth is tight - and Dolby bought one of the major contributors to the standard; they'll be marketing their own stuff branded as Dolby Pulse, which is HE-AAC with a few extras.

In terms of equipment licensing, this shouldn't be too much of a burden; there are chipsets that can do all of this work out there, and Dolby has some designs that do the whole job, with a specific intention of reducing licensing costs too.

AC3 (as opposed to E-AC3) can only handle up to 5.1 channels, so you couldn't easily do audio description that way; the way it's done on satellite is to have an AC3 track, which can be downmixed to stereo in some kit, and a completely separate stereo MPEG mix with the audio description already in there.

For those who are interested, I've been writing a fair bit about this for the last month on my Gone Digital blog.

Just an update to my earlier post. I can confirm you only get the multi channel audio via the HDMI connection not the SPDIF or COAXIAL digital output from my DMR-BW780.

The real issue I have at the moment is the fact that many broadcasts on the HD channels (大象传媒, ITV and Channel 4) appear as 5.1 multi channel when they are in fact only stereo (2.0). But this seems to be random on ITV as I noticed tonight one program was correctly output whereas on the 大象传媒 HD channel it is always output at 5.1!

This really is a very British mess that should have never been allowed to occur. It indicates the reduced level of engineering in the UK as 20 years ago this would not have happened!

The poor UK consumer loses out yet again!

Well, 20 years ago, there was stereo broadcasting, and that was it. I daresay the playout systems are a lot more complicated, with tons of metadata flowing alongside the actual audio, to control everything. There are many more things that can go wrong. I doubt, too, that the actual number of engineers to keep an eye on all these systems has actually increased in proportion with the number of services, from any broadcaster.

20 years ago 大象传媒 was the inventor and the leader of technology. They have invented the 12-bit digital encoding with 8-bit linear and 4-bit floating system so that stereo distribution to FM radio transmitters didn't suffer phasing problems. 20 years ago 大象传媒 cared about little things like that. They cared about quality. Not now!

Today technology exists and 大象传媒 buys it, using the money we give them as the license fee. Instead of buying and utilising the SOTO technology, they do everything possible to reduce the quality of their service while hiding behind a barrage of political reasons. You may have read on other blog posts how the people in charge duck the questions from viewers who care so much about quality that they went to 大象传媒 to conduct tests. The only thing they liked about their time at 大象传媒 was the hospitality. When was the last time you were impressed with the hospitality of engineers???

大象传媒 of 20 years ago would be the gurus, now they are the politicians who duck questions. No wonder 大象传媒's broadcast quality has detoriated. 大象传媒 was known to broadcast The Best TV and radio in the world. Look at the state they are in now:

DAB radio with MPEG L2 compression of such low bandwidth that it is demonstrably worse then the FM it plans to replace.

HD TV with 1440 pixel frames, low-bandwidth related artefacts and 5.1 encoded BUT stereo transmitted 'surround' audio stream.

Such a shame that the Greatness of Britain has left the British Broadcasting Corporation.

I wonder if it is time to contact the 大象传媒 Watchdog program as Freeview HD is sold as having Hi Definition pictures and cinematic surround sound (see ).

Clearly with many (maybe majority) of the products currently on the market it is impossible to obtain surround sound via the accepted connections of an optical or coaxial digital connection, as supported on all surround sound equipment.

This comment was removed because the moderators found it broke the house rules. Explain.

It would be nice if Phil Layton would join in on the comments posted on this blog!

1./ Why did they not adopt the Dolby Digital Plus standard? (Even if they started with DD then upgraded to Plus when available.)

2./ Why does the 大象传媒 HD channel flag (transmit) everything in HE-AAC 5.1 when the material is only stereo? (On ITV HD it is correctly output as 2 channel audio unless it is 5.1.)

3./ Why did they "have" to have an audio descriptor service at all on the HD channels? Since this is only used by those who are visually impaired they would not benefit from a high definition picture and could easily watch the same content on the non HD channels.

Over to you Phil.....

In response to point 3, it's because people with sight difficulties don't necessarily live alone. They may live with people who can see perfectly - probably the majority do, in fact.

It seems a bit mean to say to those people "Well, you want to watch Dr Who with your audio description, you go and sit in another room and watch the SD version, while we all watch in HD. Catch up with you in 45 minutes."

Nigel,

I do not want to be mean to those less fortunate than myself but given the low numbers affected, and the fact that the others who live with those affected could easily watch the non HD version, it would ensure the majority would not be affected. There is a tendency to be over PC these days even if this disenfranchise the majority.

In fact had the Dolby Digital system been adopted then it could have been updated to the Plus system at a latter date giving those that needed audio description the option to join HD latter.

Or have HE-AAC and switch to Dolby Digital between programs. This was discounted by Phil because of the loss of sound while switching codecs, but who would have noticed? On ITV I see a loss of the digital audio between adverts never mind between programs! Since this switching problem would have only occurred until DD+ was introduced it is only a small inconvenience by comparison to the current poor situation.

As I said before over to Phil, noticeable by his absence!

Can 大象传媒 explain me what part of my message posted At 5:11pm on 12 Jun 2010 breaks the house rules and/or why it has been referred for further consideration? It has been three full days and a full working day.

Is this a way to censor posts?

Quote Dolby Digital Plus Wiki: Dolby Digital Plus bitstreams are not backward compatible with legacy Dolby Digital decoders, and decoders that output audio over legacy S/PDIF connections must transcode the bitstreams to an older format such as PCM, AC-3, or DTS.

So if in the future there is a move to DD+ EAC3 there will still be the same problem for those of us that love our Old Legacy SPDIF connected AV amps (Nakamichi AV8).

Most of the current boxes proudly proclaim Dolby Digital 5.1 but do not transcode and when asked the initial response was simply that they comply with DD and will decode DD5.1 when it is broadcast.

So that means NEVER.

Some manufacturers have now said they will look into providing a firmware update in the future but no firm date of when this may happen. Currently no FreeView+HD box transcodes to DD5.1 via SPDIF (at least that I have found).

Has anybody got a working 5.1 system that uses a current FreeView+HD box and any current AV Amp ?
If Yes, what percentage of the installed user-base of 5.1 equipped consumers does this represent ? Not many is my guess.

Pete

Most of the manufacturers I've spoken to say that their boxes will convert E-AC3 (Dolby Digital Plus) to AC3 (Dolby Digital), so that shouldn't be too much of an issue. You don't have to do a full transcode in that case, according to Dolby papers I've read. And, in fact, it seems that a lot of them put their effort into doing that, rather than worrying about AAC audio.

So, if DD+ were to be used, I don't anticipate there being much of a problem; you should get AC3 via SPDIF from most (if not all) kit. Unfortunatley, in the month I've been writing about this, it's also become clear that you have to dig quite deeply with many manufacturers to even get to people who know the difference between all the formats.

The Philips/Pace and Vestel T8300 (aka Bush, Linsar and some others) do provide a Dolby Digital output from Freeview HD at the moment

After reading Nigel's excellent blog entry and 大象传媒's above post I had enough and called Consumer Direct (CD), which is a telephone version of the Citizen Advive Bureau. I had posted about this last week, but for reasons only known to them 大象传媒 had censored it. You can see the entry above 'referred for further consideration.'

I hope 大象传媒 will aloow this post.

CD agreed with me that the use of FreviewHD logo and the way Freview advertise on TV (sounds coming all around you), if consumers cannot listen HD programs in surround sound, using otherwise approved equipment (that carries te logo) it is against the trade description act. They have hence referred my complaint to Trading Standars Office (TSO).

Today I had call from TSO who had been in touch with Freeview and that they have asked Freeview to clarify the usage of the logo. The person who called me said that TSO gave Freeview 90 days to sort this "mess" (his words). He said that if they do not sort this by then they will consider taking legal action against Freeview.

As Monty Phyton had once said: "If you want to have done in this country you had to shout until you are blue in the face" :-)

Nice one Riz!

Still noticeable by his absence is Phil Layton, who started this blog but seems unable to join in and answer our questions.

I am sure now trading standards are involved everyone involved in this mess will be donning their hard hats and retreating to their bunkers!

Well done Nigel for spotting this train wreck in the first place. Shame no one in authority listened!

Thanks Nigel - Informative as ever.

I don't know about the Philips/Pace FreeView HD box but the FreeView+HD box (HDT 8520) that I had only output DD2.0 while it awaits a firmware update !

It would be nice if all manufacturers actually gave tech. specs saying exactly what was available from each digital output.
ie. HDMI : Decoded LPCM 5.1 / Pass HE-AAC 5.1 / ???
. SPDIF : DownMix PCM STEREO / DownMix DD2.0 / Pass HE-AAC 5.1 / ???

Just an example of what might be said as I really don't have a clue what any box actually provides ! ! !

It would certainly be good to have more input from the technical team, but I don't think Phil is sitting poised over the blog ready to respond to questions - he's doing his actual job, which is working in the R&D department.

I know from the PR team it took a while to get the blog done in the first place, and hopefully we'll get some responses when time and workload allow.

Labelling certainly needs to improve; I'm planning on writing something about that later this week, now that I have a bit more feedback from some of the parties involved.

It's going to be a more pressing issue next year, when mandatory transcoding comes in, and there will be equipment on sale that was tested both before and after that.

Thank's to Nigel's blog I have learned that Freeview HD are now downplaying surround sound part of the service. It's a good start but I don't think it is nowhere enough. Their TV ads are still showing viewers effected by the surround sound effects, which we know is almost impossible to get till 2011.

I have today wrote to ASA and Clearcast complaining that Freeview is missleading the public and that ad should be banned from screening. Given the way Trading Standards had been in agreement with me, I am confident that Clearcast/ASA will agree with me too.

Come on 大象传媒 sort out the problem where all your Freeview HD transmissions appear as 5.1 surround sound even when they are only stereo!

It is really noticeable during the football that the sound during the match is in full 5.1 but when you switch to the studio at half time and post match it switches back to 2.0 only so we only get the commentary from the right and left speaker! Either flag the sound correctly and drop to 2.0 or do some encoding!

It can't take much to process the stereo, via Dolby pro logic for example, into a correct 5.1 format so voices appear from the centre speaker! If the South African engineers can manage is so should you!

"If the South African engineers can manage is so should you!"

Oof! This must hurt...

Philips admits to audio problems on new Freeview HD set-top boxes

"We have been made aware that there is a potential issue with the sound quality on the DTR5520 and HDT8520 boxes. Although the default audio setting is PCM (stereo), which works perfectly, customers may experience problems with sound quality if they change the audio settings to Dolby Digital ouput."

"As a temporary measure, we advise customers to keep the default PCM audio settings (as specified in the user manual), until the appropriate software is available later this year, probably in September. We apologise for any inconvenience this may have caused."

"The 大象传媒 and its suppliers have been working on a solution for switching between 2.0 and 5.1 at programme boundaries. As with all changes this has to be introduced in a controlled manner. [...] If the testing goes well then the feature will be introduced as part of a planned upgrade."

Thank you for the confirmation that you are aware of the problem and working on it. But why haven't you noticed this during the beta trials in London?

Stereo (2.0) and surround (5.1) programmes co-existed for a VERY long time. Surely 大象传媒 with all the experience would have thought of this FROM THE BEGINNING OF THE TRIALS! Not after the service is made available nationwide.

I live on Skye and receive Freeview and main 大象传媒 radio stations via the Scriaig transmitter on the island. We have had two recent transmission blackouts and no informatiom provided, indeed they havent even acknowledged that their has been a break in transmission.. When trying to get info from the 大象传媒 help site, having given my postcode, the response is basically that our info says that you will not receive a signal from this transmitter! So the population of Skye is receiving freeview tv and the main 大象传媒 radio stations from a transmitter
unknown to the 大象传媒 so to speak!

Anybody out there able to shed some light on this phenomenon!

"The 大象传媒 is required to provide an audio description service on 大象传媒 HD. Typically
there are two to three programmes everyday which are audio described. In order to achieve this we have to use the HE-AAC/AAC audio codec present in Freeview HD receivers. "

I support broadcast of AD but his doesn't explain why the 大象传媒 choose AAC and not DD. it just states that there are ~3 programs a day require AD and that the 大象传媒 broadcast the main 5.1 and AD in a codec that isn't supported by AV decoders. Going forward the suggested solution to this is to transcode the output to DD but surly this second generation DD encode would negate any efficiency/quality gain of the initial AAC, raising the question why DD isn't used to start with? From a PR perspective it would have been better to just stick to stereo broadcast than a incompatible 5.1 . DD has been well supported in AV hardware since given its first outing circa 1995, AAC has little support and HDMI PCM has only appear in last few years. I can't understand why AAC was chosen.