On Tue, 3 Jun 2003, Steven M. Schultz wrote: >> From [EMAIL PROTECTED] Mon Jun 2 22:39:54 2003 >> > Hmmm, the common problem mentioned has been "splotches of grey" in >> > low light scenes - hadn't heard 'ghosting' mentioned before. >> >> That's the same problem, just differently described. If you look at >> each individual P or B frame, there are "splotches of grey" where, >> er, things > > Similar symptom but slightly different problem. Hmmm, how does one > view standalone B and P frames? I know I frames can be decoded and > viewed by themselves but not the other types.
I don't seem to be doing a great job of describing this; maybe I should generate a sequence of images from the DVD material... Anyway, my "individual P or B frames" I meant the final produce of the decoding of the I-frame and the sequence of P and B frames leading up to that point -- using single-stepping the decoder output. I hope that's a clearer description of what I was doing. The effect seems pretty much decoder independent as well, either a (forgiving[1]) hardware, or the mplayer or xine software players. [...] >> through my current set of DV sources and see if I can find a sample >> that has this issue. Sadly, I only watched 'Baby Cart in Hades' after >> I deleted the raw DV; it shows this really, er, well. > > I see later on that you mentioned the data originated as analog from > broadcast TV of a movie that probably wasn't the highest quality in > the first place. It was analog cable, not over-the-air, and there are no real transmission artifacts visible to the eye, even when closely studied. OTOH, it is analog cable and a composite stream from the cable codec box to the DV codec box... [...] > I think part of the problem you're having is that "-N 1.5" and "-Q > 1.5" are combining to toss out a lot of information and '-q 2' is then > being very careful with whatever quality still remains. > > As it turns out the "-N 1.5" setting is more aggressive than the > comment "mild noise reduction" would indicate. > > You'd be far better off using "-N 1.0 and -q 4" or similar. Well, that's what I am trying with my current encoding. >> I have tried, previously, to find a rough guide to what -q value to >> give for fitting a given length of time to a target size, but failed. > > When you specify "-q" you're telling the encoder to use VBR encoding. > At that point "-b" sets the MAX bitrate, and "-q" says how hard to > push the encoder UP TO the MAX. *nod* Having discovered the '-v 1' option to mpeg2enc which spits out the quantizer used for each frame, using -N 0.5, no -Q and -q 4 produces a *much* more stable series of quant values than the previous settings did. I think I have the time to compare the results with 'preaching to the perverted', which has an awful lot of darkness scenes in it as well. >> Is there any rough guideline you can suggest for trying to pick the >> quantizer? > > Sure - I've never been known to back away from expressing an opinion > or two ;-) > > This assumes that the target is a DVD. It is. I still figure that broad compatibility is better than the quality improvement that MPEG-4 would get me. :) [...] > For DVD with good quality sources I use either "-q 5" (for more > playtime on a single disc) or perhaps 4 (if I know that I have lots of > space). -N between 0.5 and 1.0 (higher setttings are useful for low > quality sources or if the destination is VCD). > > On one set of DVDs I'm in the process of creating now I only need to > fit about 1hour maximum of video on a DVD - thus the only constraint I > have is to keep the bitrate under the legal DVD maximum. "-q 4 -N 0.6 > -b 8500" is working well with the average around 7700 and peaks up to > ~8700. So, on a relatively low noise source, with an hour and a half, I probably want to use -q 5 to get a decent output size, with around 10% overhead on the bitrate cap? [...] >> So, either this is some sort of noise effect in the source as was >> suggested, and so specific to the source, or I need darker material >> to play with. > > So it's specific to the one movie. That really makes it sound like > there is something not 100% right with the original movie that started > the thread. *nod* That is looking more likely all the time. >> Sadly, I don't have the DV source to that movie around any longer; it >> only occurs very occasionally in things and I don't tend to keep the >> source around for long after encoding finishes. > > At 12GB/hr (for NTSC at least - PAL's a bit larger) *nod* The source is, for reference, PAL DV, with me in Australia. > I can understand not keeping stuff around for a long time. Couple > weeks ago I bought a 200GB drive (with discount and rebate it was only > US$149) and it's 59% full already. Time to start doing some encoding > and reduce the backlog ;) That also makes me jealous. I am still waiting until the price on the 250GB Firewire drive I use drops below the AU$700 mark before I can get a second of them. That will make life much nicer. [...] >> I noticed you discussing that the other day -- my video source is an >> analog to DV bridge box converting footage broadcast via analog cable > > Canopus or one of the other similar units? Yes, the DAC-100 from DataVideo <http://www.datavideo-tek.com/> >> television, so it's generally pretty good quality.[1] > > Digital TV or analog? In the US, at least where I live, broadcast > (over the airwaves rather than cable) TV is fairly to very poor > quality. Over the air broadcast stuff is of variable quality, and kind of marginal in the area I live in. Our cable is supplied over physical cable, however, from the source and so the quality is quite good. Thanks for your help. I will report what I can learn from all of this. Daniel Footnotes: [1] This DVD player happily plays not-quite-right AC3 streams and ignores IFO hacks that make other players give up... -- Moloch whose mind is pure machinery! Moloch whose blood is running money! Moloch whose fingers are ten armies! Moloch whose breast is a cannibal dynamo! Moloch whose ear is a smoking tomb! -- Allen Ginsberg, _Howl_ ------------------------------------------------------- This SF.net email is sponsored by: Etnus, makers of TotalView, The best thread debugger on the planet. Designed with thread debugging features you've never dreamed of, try TotalView 6 free at www.etnus.com. _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
