Dolby Pro Logic II (2 channel) vs 6 Channel Discrete?

[Henry Hall]

What is best for 5.1 surround sound, "Dolby Pro Logic II" (2 channel), or "6 Channel Discrete"?
After encoding the overall file size is almost the same, so which would give the best overall surround sound effect?

Many Thanks!

[Deleted User 11865]

6-channel discrete features 6 discrete channels (as opposed to matrixed-encoded into 2 discrete channels), so channel separation will be better.

[mithrandir]

Depends on what audio bitrate you are using. At or under 256 kbps, Dolby Pro Logic II will be better than 6 channel discrete.

Also what is your source? DVD? If so then use "Auto Passthru" instead of "6 channel discrete" because there is no sense in transcoding an AC3 5.1 track (which will never be above 448kbps). 6 channel discrete is useful OTOH when your source track is high-bitrate (1536kbps) DTS or an HD audio track on a blu-ray disc.

[Henry Hall]

The source is DVD and the audio is AC3 5.1 Dolby digital.
I am converting to H.264 in .mp4 container.
I want to run the converted file on my PLEX server (home media server). However I want to stream the file to an Xbox 360. Xbox 360 only supports AAC (Dolby Surround, Dolby Pro Logic II, 6 channel discrete). It does not support AC3. Which one is best for a) DVD and b) BluRay. ?

[mithrandir]

Use 6 channel discrete then for both DVD and Blu-ray. Make sure to select "AAC (ffmpeg)" instead of "AAC (faac)"; the ffmpeg implementation seems better than faac's.

[Henry Hall]

Ok thanks. Also whats the best bit-rate? I'v been using 320kbps with 6 channel discrete. Think that is good enough?
Also again what is best for when the source is 2 channel. Pro Logic II or 6 channel discrete. I notice that when I set 6 channel discrete for when the source is 2 channel, the converted file is still only 2 channels.

[Deleted User 11865]

Use 6 channel discrete then for both DVD and Blu-ray. Make sure to select "AAC (ffmpeg)" instead of "AAC (faac)"; the ffmpeg implementation seems better than faac's.

The Libav AAC encoder ("AAC (ffmpeg)") doesn't do 5.1/6-channel; or rather, it does but he output is unusable so we disable it (if you request 6-channel with that encoder, you get DPL2 instead).