Dolby 5.1

I didn’t mean to start an argument. All of my TV’s have a AC3 decoder built in. I was claiming that AC3 pass through worked on my TV’s. That’s all. If I offended anyone I’m sorry…

No offence - just trying to explain to some why 5.1 support is not a simple drop the 2.0 audio and keep the source 5.1 audio.

Unless the Tablo simply recorded the AC3 audio and then downmixed and sent stereo on the fly when requested.

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Why not have an audio setting in the Tablo settings? You decide whether to record audio as 2.0 AAC or 5.1 AC3; no need to have Tablo record both or down mix the AC3. I suppose it may break compatibility with some devices (tablets, computers, etc.), but then how do digital movies work (do they include both audio streams)? What does Tivo do?

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  1. Transcoding the 5.1 audio to 2.0 on the fly for playback would use a tuner. So if you have 2 shows recording at one time say on a dual tuner then you would not be able to watch any recordings during this time.
  2. Interesting idea for those who have only devices that decode 5.1 audio. But yes, it would break playback for many people who have Rokus whose HDTVs cannot decode 5.1 audio nor have an AVR (like me). I agree with leaving the option to the user is a good idea, but you would still have people who would complain they lost some device support.

I am all for 5.1 audio, I just think it’ll take some time to be implemented nor should it be a priority over support for other devices and UI improvements like multi-delete.

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I am not understanding how the device downmixes the audio while it is recording without using an additional tuner then. I mean it is tuning the channel with one tuner, and it is already mixing that audio to stereo on the fly while recording to the harddrive. So why would it NOT need an additional tuner to downmix from an OTA signal, yet NEED an additional tuner to downmix from the Harddrive?

EDIT: Maybe I have been mistaken all along about this device. I have been under the impression that if both tuners are recording, I can not watch a recording. Are you saying that I do not need a free tuner to watch a recorded video??? If that is the case then OMG I have been carefully NOT watching recordings while recording with both tuners all this time for nothing.


“EDIT: Maybe I have been mistaken all along about this device. I have been under the impression that if both tuners are recording, I can not watch a recording. Are you saying that I do not need a free tuner to watch a recorded video??? If that is the case then OMG I have been carefully NOT watching recordings while recording with both tuners all this time for nothing.”

Are you being sarcastic? You can definitely watch recordings when the dual tuner is recording two shows. The Tablo is not doing any processing of the recordings. It is just sending it to device say a Roku.

No I was not being sarcastic. This makes things Sooo much better. I don’t know where I got the impression that I needed a tuner available but I just wish I had known this earlier. This will be well received news around here. :slight_smile:

You only need a tuner available for viewing a TV show when you use Tablo Connect.

That is probably where I got things twisted around.


Not entirely true, while using Tablo Connect if your interent upload speed is fast enough to use Full Quality for the remote streaming quality it is exactly like streaming locally. It does not use a tuner. So you can also record 2 shows at the same time.

When you set the remote streaming quality to anything lower than Full Quality a tuner is used to transcode the video from full bitrate to say 3 Mbps.

None of this is rocket science. Storing two soundtracks does not add that much to the storage footprint and I would happily make that trade every time. It would not add much overhead at all on the processing side, because the source is AC3 and they are already down-mixing it. I do not think the problem here is engineering related. I think it is priority related.

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I just know that the Tablo folks have looked at this problem for over a year now and haven’t been able to come up with a solution. If it was just programming, it would have been done by now. There is something complex about this that is causing the holdup.

All I know is that they have not released the feature. I have no idea if they have worked on it and I think it is silly to assume that they have spent a substantial amount of time on it.

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People it’s not that easy. I have gone through this. Once the code is done, you have to go through the Dolby Certification process for 2.0 and 5.1. These tests take a long time to do. Then once all the tests pass then you have to submit your findings to dolby and they run the tests again on your equipment. This all takes time! Also if there is a backlog at Dolby you have to wait for your stuff to be tested. Once that is done you get a nice letter from dolby and then you can add that feature.

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I can’t see how it isn’t a software issue. The hardware has to be able to receive, decode and then transcode the existing 5.1 audio to create the files that get stored on the drive. An option to not transcode and just use the raw MPEG streams would be just a software change away.

Yes I realize there may be a lot of effort to code the switch in, but it has to be a software issue and not hardware.

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The limitations are not exactly on the Tablo server or software side. Let’s take the most popular front end for Tablo playback, the Roku.

The Roku video player which is what actually plays back recordings cannot support 2 audio tracks in DirectPlay (this is Plex terminology but all it means is no transcoding of the video or audio, which is the goal here because we don’t want to tax the Tablo device). Whenever I playback a file locally that has 2 audio tracks, even with DirectPlay, the 2nd track can be selected before playback starts but the file is remux’d so the video stream and selected audio track can be played together. There is processing here that is done on the server side to make this happen. During playback if you hit the * button you cannot select the 1st audio track so there is obvious processing of the file even though there is no transcoding of the video or audio itself.

For the Tablo to do this, you would always lose a tuner when playing back any recording. Many of us with 2 tuners would not appreciate this as that means we only have 1 tuner available for recording or watching live TV. The reason for the loss of the tuner is that any processing done by the Tablo on a file removes the CPU power for 1 tuner.

You do not need 2 audio Tracks. DD 5.1 will fold down to 2.0 without any issue. There is too much misinformation and speculation here. There are other priorities that they are working on now. We will get 5.1 we just have to wait.

It’s troubling to hear such BS aimed at Tablo, they have done so much in a little amount of time. We will get everything we want you just need to wait.



This is not misinformation nor speculation. You do need 2 audio tracks, let me explain why below:

5.1 AC3 audio will not playback on a Roku. The Roku cannot decode 5.1 AC3 or 2.0 AC3 audio. It can only pass through the audio to the device it is connected to, and it the responsibility of said device (an HDTV or AVR) to decode the audio for playback. My HDTV does NOT decode AC3 audio over HDMI. So if I had a Tablo recording with h.264 video and 1 audio track with only 5.1 AC3 audio, I would NEVER get audio from my Tablo. The Roku can decode 2.0 AAC audio though (and without transcoding or converting requiring some CPU usage there is no way to go from 5.1 AC3 to 2.0 AAC on the fly - the Roku will NOT do this, the Tablo would have to).

Many people have HDTVs that do not decode AC3 audio over HDMI, however some do. So yes, 1 audio track could work for them.

But do you see now why 2 audio tracks would be required? My goal is not to aim BS at Tablo, but to ensure people are not misinformed and explain why this is not such a simple task as they perceive.

I find that very strange, I thought all HDTV’s decode Dolby Digital 5.1. Isn’t part of the HDTV spec?