Wrong 6 Channel AAC mapping

[Deleted User 16137]

Hi guys,

Now that I've realised my iPhone 4 can play the 6 Channel AAC tracks in videos files (albeit obviously mixed down to stereo), I've decided to encode the SD versions of my movies with a 6 Channel AAC track. This is better when using some Media Center front ends as I no longer have to flip between a stereo and multichannel audio track.

However, I've noticed during playback that the Center channel and Front-Left channel appear to be swapped.

Have you experienced this before? Do you know if it's a Handbrake bug that I can fix post production (I can tweak the mapping), or if it's a decoder issue?

[Deleted User 11865]

Activity Log please.

[Deleted User 16137]

Thanks Rodeo,

This is from the nightly release I used (I can run the same task again with the current official release if need be) as I've been experimenting with volume gain and hardcoding SSA subtitles.

http://paste.handbrake.fr/pastebin.php?show=2805

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Lion? And VLC?

I don't think it is a HB issue. Try playing the file in QuickTime (no Perian) or some other player and see what happens. Then add your voice to the VLC complaints as the issue was supposedly fixed in 1.1.12 or 1.2.0-git but seemingly hasn't.

[Deleted User 16137]

Thanks.

I'll dig a bit deeper this weekend.

But surely it's not VLC if my iPhone is down-mixing the 6ch AAC into stereo, but playing the centre channel through the left headphone.

Unless VLC is messing up the mapping during the encoding somehow?

[Deleted User 11865]

I spent a good deal of time testing AAC channel mappings. I'm 100% sure that HandBrake's AAC 5.1 output has the correct mapping as long as the source is AAC, DTS, AC3 or TrueHD.

In 0.9.5, we remap from the source mapping to the native AAC mapping using Apple-provided Core Audio functions, which are broken under OS X Lion. But we fixed it in the nightlies by using the built-in HandBrake remapping function, so that's not your issue.

The problem must be lie with the iPhone, not HandBrake.

[Deleted User 11865]

As a side note, the AppleTV is known to use some sort of Dolby Surround/ProLogic mixdown, rather than a stictly Stereo mixdown. It's quite possible the iPhone does the same. Maybe the fact that the center channel comes out of the left channel is a side effect of matrix-encoding 4/5 channels into 2 actual channels.