On Tue, Nov 04, 2014 at 20:12:56 +0100, blue...@caramail.com wrote: > XBMC WILL play Dolby encoded files correctly if the channels > are all present and not encoded in some weird format, in fact it is > very good at that.
That's understood. > It would be really great if ffmpeg could detect these channels and > reencode them to a more standard (if that is the way to put it) ac3 > format. This is the technicality which needs to be understood. If the source is what Carl Eugen has identified, there is no digital indication that this is "Dolby Surround". You will identify two channels which can be played on stereo output, and will sound like a down-mix of surround material on stereo. Yet in these two channels, there is a mixture of four or six audio channels. If you know how to "decode" them, you can separate them. Actually, you should be able to detect this surround encoding if you analyze the audio waveforms, but this may mean actually decoding them and checking whether the "extra" channels contain sound. (My hardware decoder creates pseudo-surround effects from plain stereo material by the way, due to the way it "tries" to decode 6 from 2 channels and the audio's phases.) Actually, a lot of digital TV channels broadcast their movies with surround sound like this, i.e. using two channels, but still containing surround. Mostly this is the case when they don't have 6 channels available. This is very common in broadcast, from my experience. Basically, ffmpeg currently can neither detect nor decode this encoding. I think decoding it would require something like an audio filter. > "Carl Eugen Hoyos" <ceho...@ag.or.at> wrote: > > I will hopefully open a ticket for PLII decoding, > > I have no idea how difficult / trivial this is > > given that we support encoding... Since it's easy to find algorithms (i.e. matrices) for encoding but not for decoding, I am guessing that the latter may be a much tougher task. It's not as easy as inverting the matrix. I'm no smarter than Carl Eugen concerning this. Here's the only description I have found of the process, and it looks very DSPish (if not analog): http://www.eetimes.com/document.asp?doc_id=1225389 See figure 5 for a summarizing diagram. No C source code provided though. ;-) Moritz _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user
