[Libav-user] E-AC-3 7.1 encoding?

[David Henry]

I'm wondering about encoding E-AC-3 7.1 surround using CODEC_ID_EAC3, but couldn't find any sample code.
If supported, when was this feature added? (i'm using libavcodec   53. 42. 4) 
I'm thinking that I select: 
CODEC_ID_EAC3 as the codec,
AVCodecContext.channels = 8
AVCodecContext.sample_fmt = AV_SAMPLE_FMT_FLT
AVCodecContext.channel_layout = AV_CH_LAYOUT_7POINT1
and then just encode as I would any other audio using avcodec_encode_audio().
Are there any extra steps or gotchas when trying to encode 7.1 surround?