On Sun, 2006-08-27 at 21:55 +0100, `Zidane Tribal wrote: > On Sun, 2006-08-27 at 19:03 +0100, `Zidane Tribal wrote: > > hello all. > > > > I'm trying to put together various dvd's with 5.1 ac3 audio tracks. > > Can anyone point me in the right direction to some documentation on how > > i would normalise the audio? > > > > Basically, some of the video's are too loud, others too quiet. I know > > transcode itself will let me increase or decrease the volume by a > > specific amount, but i would need to discover how much i need to inc/dec > > each track and then re-transcode the audio adjusting each track by a > > specific amount. what would be really spiffy is something like > > normalise in batch mode, which would allow me to have, say, 10 ac3 > > tracks, scan them all and normalise them all to 12db. > > > > does such a thing exist? if not, can anyone point me towards some > > documentation on how to convert ac3 5.1 surround into different channels > > so i can normalise them as wavs, then re-mux and transcode them back > > into an ac3? > > > > any help would be much appreciated. > > > > `Zidane. > > > > > > > ok, now i know i'm replying to my own mail, but hopefully this should > keep it in the same thread ;) > > after much man-page reading and fiddling around, it would seem i can use > mplayer to extract each individual audio track in turn, as follows: > > mplayer -channels 6 -af channels=1:1:1:1 ./x-men-1.vob > mplayer -channels 6 -af channels=1:1:2:1 ./x-men-1.vob > mplayer -channels 6 -af channels=1:1:3:1 ./x-men-1.vob > (etc... for all six channels) > > where:- > > mplayer -channels 6 > -af > channels=no-of-output-channels:no-of-routes:map-channel-X:to-channel-X > > now i can get each channel out on its own, it shouldn't be too much > trouble to fiddle around with transcoding it to, say, wav, and using > something to normalise it. > > however, this leads me to another curious quandry. after digging > around to try to find out which channel number represented which > 'speaker', i came accross the ac3 spec here > http://www.atsc.org/standards/a_52b.pdf which implies there can be 8 > different track layouts (table 5.8 is the part that defines them). so, > the question now becomes, does anyone know of a tool that can give me > the 'acmod' feild, so that i know which track is which? preferably > something cli-based, as i want to incorperate this into a shell script. > > many thanks in advance if anyone can point me in the direction of > something that could tell me which trach is which 'speaker'. > > `Zidane. >
ok, for those who are following the only thread where one person answers his own questions, you'll be glad to know the men in the white coats are on the way ;) on a more on-topic note, in a blinding flash of inspiration, i realised i'm over-thinking the problem :) rather than having to identify the tracks, i can pull them out, normalise them, then put them back in the right order. i dont need to know what each track is, just make sure i maintain the order of the tracks. i noticed someone asked on the wiki whether a procedure exists to normalise 6 channel ac3 audio. there is now :) i'll list it here and put it on the wiki just as soon as i make sure all the levels are normalised ok and find the email that gives me the editing instructions. to normalise 6 channel ac3 audio tracks.... (note: a couple of parts of this are shamelessly copy/paste'ed from the wiki and the http://mightylegends.zapto.org/ pages) Find out if the original .avi/.mpg file already contains a 5.1 AC3 audio track: mplayer -vo dummy -identify movie.avi 2> /dev/null | grep 5.1 A positive output would look something like: AC3: 5.1 (3f+2r+lfe) 48000 Hz 384.0 kbit/s If it does, then extract it using 'tcextract' tcextract -d2 -i movie.avi -a0 -x ac3 | tcextract -d2 -x ac3 -t raw > movie.ac3 once this has been extracted, use mencoder to extract each individual track into a pcm wav. mplayer -channels 6 -af channels=1:1:0:0 -ao pcm:waveheader:file=track0.wav -vc null -vo null ../movie.ac3 mplayer -channels 6 -af channels=1:1:1:0 -ao pcm:waveheader:file=track1.wav -vc null -vo null ../movie.ac3 mplayer -channels 6 -af channels=1:1:2:0 -ao pcm:waveheader:file=track2.wav -vc null -vo null ../movie.ac3 mplayer -channels 6 -af channels=1:1:3:0 -ao pcm:waveheader:file=track3.wav -vc null -vo null ../movie.ac3 mplayer -channels 6 -af channels=1:1:4:0 -ao pcm:waveheader:file=track4.wav -vc null -vo null ../movie.ac3 mplayer -channels 6 -af channels=1:1:5:0 -ao pcm:waveheader:file=track5.wav -vc null -vo null ../movie.ac3 this should leave you with 6 files, track 0 through 5. now, time for some normalisation (yay! linux can make me normal! no more talking to myself on mailing lists!) normalise-audio -b *.wav we use batch mode (-b) on the normalisation process for a reason. namely, the 5.1 soundtracks are balanced, you dont want all of them at exactly the same volume. batch mode reads the average levels of all the files, then calculates *one* increase, and applies the same increase to all files, rather than normalising each file individually. once we are normal, we bunch all the tracks back up into a 6 channel ac3 file with multimux and ffmpeg. multimux track0.wav track1.wav track2.wav track3.wav track4.wav track5.wav -o final.wav ffmpeg -i final.wav -ab 448 -ar 48000 -ac 6 final.ac3 and there we have our shiny normalised ac3 soundtrack, with all the channels increased or decreased in volume :) its a little kludgey, bit it appears to work. time for me to go get some sleep and let transcode do its thing. `Zidane (sleep deprived, sanity torn and tattered).
