I have been experimenting with 5.1 audio encoded in Vorbis, and I found that MPlayer can't automatically downmix 5.1 Vorbis audio to stereo, like in AC3 or DTS. It seems that it leaves this task to the decoder, and since the decoder can't do the downmixing, MPlayer simply discards all but the left and right channels. To workaround the problem, I tried to use the pan filter with these settings: -channels 6 -af pan=2:1:0:0:1:0.5:0:0:0.5:0.7:0.7:0:0 My first problem was to find out what channel order was being delivered to the filter, the order was obviously different from what Vorbis specify for 5.1 audio. After some trial and error, I found the order. The remaining problem was to find what values to use. At first I did a guess, but the final values were suggested in this forum thread: http://www.blender.org/forum/viewtopic.php?t=16557 These values worked fine for the movie Elephants Dream from that thread, but when I played another movie in my TV via HDMI, whose audio I converted from DTS to Vorbis, I get some strong noise in the parts where LFE is strong (even if the pan filter, like above, is configured to discard the LFE channel). There is no such problem when using the default DTS dowmixing facility. So, do you know what may be causing this strong noise effect? Should the fact that MPlayer can't automatically downmix from 5.1 to stereo be considered a bug? -- Lucas Clemente Vella lvella at gmail.com.br
