New 1080p encode for Elephants Dream

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lvella
Posts: 10
Joined: Wed Jan 21, 2009 6:50 pm

New 1080p encode for Elephants Dream

Postby lvella » Wed Jan 13, 2010 5:51 am

Not happy with the quality of the biggest Elephants Dream version available in the official website (AVI, MPEG4 / AC3 5.1 Surround, 815 MB), I wanted to create a better version. I downloaded the original lossless video and audio and made a brand new encoding. It ended up smaller than the "official" and with much better perceived quality.

Can grab it via torrent:
http://thepiratebay.org/torrent/5275493

Vorbis is the best lossy audio codec commonly available, but it is not a very common choice for 5.1 audio. I wanted to take the risk, because I am not a fan of proprietary formats and there is no good open source AAC encoder. The problem I found is that at least MPlayer can not automatically downmix the 6 channels into 2 channels for those who don't have a 5.1 setup. For now, I have to workaround the problem with:

Code: Select all

mplayer -af pan=2:1:0:0:1:1:0:0:1:0.5:0.5:0:0 movie.mkv


Please let me know if you have audio issues with other players...

Jan Morgenstern
Posts: 9
Joined: Sat Nov 03, 2007 6:12 pm

Re: New 1080p encode for Elephants Dream

Postby Jan Morgenstern » Fri Jan 15, 2010 12:31 pm

Hi,

lvella wrote:Vorbis is the best lossy audio codec commonly available, but it is not a very common choice for 5.1 audio. I wanted to take the risk, because I am not a fan of proprietary formats and there is no good open source AAC encoder. The problem I found is that at least MPlayer can not automatically downmix the 6 channels into 2 channels for those who don't have a 5.1 setup. For now, I have to workaround the problem with:

Code: Select all

mplayer -af pan=2:1:0:0:1:1:0:0:1:0.5:0.5:0:0 movie.mkv



out of interest, what's the channel order in your Vorbis stream? From the downmix settings above, it looks like it's L R Ls Rs C LFE, which would be different from the Xiph specification (L C R Ls Rs LFE). In any way, to replicate the stereo downmix settings of the original, C should be mixed at -3 dB and the surrounds at -6 dB, respectively. So, assuming that my guess about your channel order was correct, the line should be more like

pan=2:1:0:0:1:0.5:0:0:0.5:0.7:0.7:0:0

The reason we chose AC3 for the online releases of ED and BBB is that it's still the only multichannel format that has a solid downmixing facility built in (AAC comes close, but some players still mess it up).

lvella
Posts: 10
Joined: Wed Jan 21, 2009 6:50 pm

Re: New 1080p encode for Elephants Dream

Postby lvella » Fri Jan 15, 2010 4:26 pm

Jan Morgenstern wrote:out of interest, what's the channel order in your Vorbis stream? From the downmix settings above, it looks like it's L R Ls Rs C LFE, which would be different from the Xiph specification (L C R Ls Rs LFE).


The channels are in correct order, following Vorbis spec (L C R Ls Rs LFE), but mplayer rearranges the channels' order before passing the audio through the filters. Amazingly enough, this rearranged order is different for AC3 and Vorbis, so this filter only works with Vorbis.

Jan Morgenstern wrote:In any way, to replicate the stereo downmix settings of the original, C should be mixed at -3 dB and the surrounds at -6 dB, respectively. So, assuming that my guess about your channel order was correct, the line should be more like

pan=2:1:0:0:1:0.5:0:0:0.5:0.7:0.7:0:0

The reason we chose AC3 for the online releases of ED and BBB is that it's still the only multichannel format that has a solid downmixing facility built in (AAC comes close, but some players still mess it up).


Thanks for the info. This downmixing facility of AC3 you speak of is in its specification? Has AC3 a facility for the audio creator to specify how the downmix should be done?

Given the right channel order, would it be good to hardcode this downmix setup (pan=2:1:0:0:1:0.5:0:0:0.5:0.7:0.7:0:0) inside ffmpeg Vorbis decoder to solve the problem of most players? (I am assuming that ffmpeg has interface to request the number of channels you want, I really don't remember if it works like that.)

Jan Morgenstern
Posts: 9
Joined: Sat Nov 03, 2007 6:12 pm

Re: New 1080p encode for Elephants Dream

Postby Jan Morgenstern » Fri Jan 15, 2010 5:29 pm

lvella wrote:The channels are in correct order, following Vorbis spec (L C R Ls Rs LFE), but mplayer rearranges the channels' order before passing the audio through the filters. Amazingly enough, this rearranged order is different for AC3 and Vorbis, so this filter only works with Vorbis.


Oh, I see. That's weird. :)

Thanks for the info. This downmixing facility of AC3 you speak of is in its specification? Has AC3 a facility to the audio creator specify how the downmix should be done?


Yeah, it's part of the bitstream info in the frame header. Valid values are -3, -4.5 and -6 dB for the center channel, and -3, -6 dB and "discard" for the surrounds.

Given the right channel order, would it be good to hardcode this downmix setup (pan=2:1:0:0:1:0.5:0:0:0.5:0.7:0.7:0:0) inside ffmpeg Vorbis decoder to solve the problem of most players?


Yes, I'd say that's the most sensible default for a 5.1-to-stereo downmix if there's nothing known about its origin.

lvella
Posts: 10
Joined: Wed Jan 21, 2009 6:50 pm

Postby lvella » Thu Jan 21, 2010 3:43 pm

A lot of people already downloaded this version of the movie, and I tend to believe most of them are from this forum. What do you think of it? Is it worth to be listed in the download page of Elephants Dream?


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