# Roamio supports multi-channel AAC?



## sirfergy (May 18, 2002)

I generally re-encode movies for my TiVo into H264+AC3, but would like to use H264+AAC so all my devices can play it back. Does the Roamio correctly support multi-channel AAC? I know the Premiere didn't, but I'm hoping they've improved that functionality with the Roamio.


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## Dan203 (Apr 17, 2000)

I don't think so. And even if it did it would be down mixed to 2ch PCM anyway since no receiver I'm aware of supports multi-channel AAC bitstreams.

Why not just encode the movies to have both AC3 and AAC and let the device pick the one it can play?


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## Zu Nim (Apr 20, 2012)

Maybe relevant because the OP might not want multiple audio tracks.

I found that several TiVo software releases ago, my (decrypted) iTunes TV shows and movies never play the AC3 track anymore. I have to manually switch to the AAC track. Anyone else experience this?


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## jcthorne (Jan 28, 2002)

Tivo plays 2 channel AAC but decodes it to 2 channel PCM for digital output. Cannot decode 5.1 AAC and neither do any TVs or home theater recievers that I know of.

Tivo does work with 5.1 AC3 and outputs that to the tv or receiver on hdmi or digital audio out.

The mp4 spec has supported ac3 for many years and most recent devices that support mp4 files with h264 support ac3 audio. Android does, my WD Tv streamer box does. I know some apple devices do not, no idea why. Apple wrote the spec and then decided not to support it.

Never had any consistant luck with Tivo selecting the correct audio track with mp4s using multiple tracks.


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## cherry ghost (Sep 13, 2005)

All my encodes are in the same format and I always get 5.1 on my TiVo when pushed/pulled with pyTiVo


```
Stream #0:0(und): Video: h264 (High) 

Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 128 kb/s 

Stream #0:2(und): Audio: ac3 (ac-3 / 0x332D6361), 48000 Hz, 5.1(side), fltp, 384 kb/s
```


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## moyekj (Jan 24, 2006)

cherry ghost said:


> All my encodes are in the same format and I always get 5.1 on my TiVo when pushed/pulled with pyTiVo
> 
> 
> ```
> ...


 Out of curiosity, does the TiVo see the secondary aac stream as available? i.e. While playing it back using right arrow are you able to select alternate audio stream? I'm assuming you are pushing mp4 as is with pyTivo and not having it transcode to mpeg2 or remux to transport stream container (ts=on in pyTivo) which is probably throwing out the aac stream?


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## cherry ghost (Sep 13, 2005)

moyekj said:


> Out of curiosity, does the TiVo see the secondary aac stream as available? i.e. While playing it back using right arrow are you able to select alternate audio stream? I'm assuming you are pushing mp4 as is with pyTivo and not having it transcode to mpeg2 or remux to transport stream container (ts=on in pyTivo) which is probably throwing out the aac stream?


No alternative audio available. When I right arrow, it shows

"The current audio track is: Unknown - Dolby Digital
There are no alternative audio tracks available."

I have "ts=on" and under HD TiVo Settings-->audio_lang: "5.1, DTS, en"

When I push, I get


```
Stream #0:0(und): Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 1280x720 [S
AR 1:1 DAR 16:9], q=2-31, 16384 kb/s, 59.94 fps, 60k tbn, 60k tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: ac3 ([165][0][0][0] / 0x00A5), 48000 Hz, 5.1(side),
 448 kb/s
    Metadata:
      handler_name    : SoundHandler
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:2 -> #0:1 (copy)
```


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## moyekj (Jan 24, 2006)

cherry ghost said:


> No alternative audio available. When I right arrow, it shows
> 
> "The current audio track is: Unknown - Dolby Digital
> There are no alternative audio tracks available."
> ...


 Yes, so pyTivo is filtering out the AAC audio track and including AC3 track as part of the TS remux. If you use PUSH method to push the mp4 file natively you may find you will get the AAC track on TiVo since it's 1st one in your encode - I think last I tried a while ago TiVo just goes for 1st audio track instead of specifically looking for AC3 track.


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## cherry ghost (Sep 13, 2005)

moyekj said:


> Yes, so pyTivo is filtering out the AAC audio track and including AC3 track as part of the TS remux. If you use PUSH method to push the mp4 file natively you may find you will get the AAC track on TiVo since it's 1st one in your encode - I think last I tried a while ago TiVo just goes for 1st audio track instead of specifically looking for AC3 track.


If I remove "5.1, DTS, en" from HD TiVo Settings-->audio_lang and leave it blank, the TiVo does show two audio tracks, Unknown and Dolby Digital. I get sound with Unknown but not with Dolby Digital. My receiver shows Unknown as PCM and DD as None.


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## moyekj (Jan 24, 2006)

Right, so looks like for that case TiVo is using AAC (1st audio track) and doesn't know how to switch to the AC3 track.


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## Zu Nim (Apr 20, 2012)

Actually, the AAC track works and the AC-3 track doesn't, but TiVo will use the AC-3 track by default. If I switch to AAC, I get sound.

Now if I use "ts = on" to force a remux of just AVC and AC-3, the AC-3 track will play. So it doesn't seem like TiVo has a problem playing the AC-3 track (or the AAC track), but it breaks when there are both. It used to work a few TiVo releases ago, at least for me. I should see what flags are being changed during the remux.


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## moyekj (Jan 24, 2006)

Zu Nim, in your encodes which audio track is 1st, AAC or AC3? It was my impression that if you make AC3 the 1st sound track then TiVo will pick it up properly without needing any pyTivo tricks.


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## Zu Nim (Apr 20, 2012)

moyekj said:


> Zu Nim, in your encodes which audio track is 1st, AAC or AC3? It was my impression that if you make AC3 the 1st sound track then TiVo will pick it up properly without needing any pyTivo tricks.


They're in AAC/AVC/AC-3 order. It can play the AAC track because I can manually switch to it. If I use ffmpeg to remux it so there's only the AC-3 track, it can play that. So no problem with the codecs or the audio path from the TiVo to the TV.

But when both audio tracks are muxed, it doesn't play the AC-3 track even when it's selected.

Both audio tracks are in the same alternate group (1) and the AAC track is enabled while the AC-3 track is disabled. They're both English, although the TiVo says they're Unknown.

I've tried enabling the AC-3 track and disabling the AAC track. No change.


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## moyekj (Jan 24, 2006)

Yes, so behavior is still essentially TiVo will only use the 1st audio track in the encode, so you better make that AC3 if you want multi-channel audio, or use pyTivo tricks to filter out AAC tracks that are in 1st spot.


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## Zu Nim (Apr 20, 2012)

It's worse than that. It starts with the second track selected but won't use it. It'd be much better if it selected the first track, but it doesn't. It's annoying and confuses the hell out of my guests. But yes, the workaround seems to be to force pyTivo to remux it to a single audio track, something I'm learning how to do thanks to this thread. And wait for TiVo to fix the multitrack audio support it broke... I won't hold my breath.


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## cherry ghost (Sep 13, 2005)

moyekj said:


> Yes, so behavior is still essentially TiVo will only use the 1st audio track in the encode, so you better make that AC3 if you want multi-channel audio, or use pyTivo tricks to filter out AAC tracks that are in 1st spot.


I used to encode with AC3 first, but starting with iOS7 found that my iPad wouldn't accept some videos where AAC wasn't the first track. It wasn't happening with every video and I couldn't figure out what was causing it so I switched to AAC first. Remapping the ones that wouldn't work on the iPad was easy but time consuming.


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