Wikipedia:Reference desk/Archives/Computing/2012 October 8

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October 8

Ogv issues

Apparently there are some issues with these two videos. Please see: Talk:Phodopus#Please place, where it says "...What you've done is to upload a hi-res video (4x the recommended area) and told it to display as a thumb. That doesn't compress, so it still tries to come in at 7.12Mbps...". I really haven't a clue what to do. Please, please enlighten me. "Obi-reference-desk-onobi, you are my only hope." Anna Frodesiak (talk) 02:51, 8 October 2012 (UTC)

Sorry if the above question is about Wikipedia. Are questions here only to be about computers? Anna Frodesiak (talk) 03:46, 8 October 2012 (UTC)

Well, questions on Wikipedia policies belong over at the Help Desk, yes, but if your question is how to create a lower resolution version of your movie, we could possibly help with that. What movie editing software do you have  ? Also, what's the diff between the two videos you posted on the right ? The most obvious way to reduce the size of that movie is to trim off the edges. There's nothing of interest going on outside the disc, is there ? StuRat (talk) 14:08, 8 October 2012 (UTC)

They both play instantly for me, and while I'm in a comparatively affluent western country, my broadband connection is nothing special. My guess is that Stfg was or is having software or local network issues himself. That said, you can of course get help reducing the size of the video. ¦ Reisio (talk) 18:45, 8 October 2012 (UTC)

I just drag-n-dropped the video into Miro Video Converter 2.5 and selected Theora format and let it do its thing. It doesn't seem to have options. Thanks for the replies. Anna Frodesiak (talk) 23:29, 8 October 2012 (UTC)

@Reisio, thanks for looking into this. I think my software issues are solved, as I can play the lower-res videos, and my broadband checked at 9.4Mbps at a time when I couldn't view Anna's which requires 7.12 Mbps. What I don't quite grok is how Wikipedia:Creation and usage of media files#Limitations and Implementation Issues is counselling to stay below 1Mbps to keep within the "ability of Wikipedia or the Commons to deliver ...", when the obviously approved videos at Commons:Media of the day are going so much higher -- those fine magpies are asking for 33.05Mbps, no less. What throughput does the server end typically achieve? --Stfg (talk) 00:18, 9 October 2012 (UTC)

Questions for those better informed than I, but I will say it's fairly apparent that in-browser video support is less than perfect at this point, particularly in regard to prebuffering. ¦ Reisio (talk) 15:50, 9 October 2012 (UTC)

I am mildy curious how http://dl.dropbox.com/u/98754825/dhrod_q06.ogv.tar would compare, however. It was generated with the following command:
ffmpeg -i Dwarf_hamsters_running_on_disc.ogv -vcodec libtheora -q:v 6 -an -vf crop=544:480:88:0 dhrod_q06.ogv
¦ Reisio (talk) 16:23, 9 October 2012 (UTC)

Windows movie editing software to change aspect ratio ?

See Wikipedia:Reference_desk/Computing#My_iphone_4.27s_camera_shot_the_video_in_disarray.2C_now_i_need_help_editing_the_vid. They've now clarified what they want, so does anyone have any recommendations ? StuRat (talk) 14:15, 8 October 2012 (UTC)

Blu-Ray vs. Pirating

How large is a typical 1080p movie file on a purchased Blu-Ray Disc? Suppose if one illegally torrents a 1080p Blu-Ray rip of the same movie, is that the exact same quality as one would receive if one purchased it instead? I suppose the file format has something to do with it right? Frequently, one can find .avi's and .mp4's and .mkv's. Which one is best? Why is there such a size discrepancy between the file types (s22 gb vs 2gb)? Thanks. Acceptable (talk) 20:09, 8 October 2012 (UTC)

Are you suggesting we give you advice on the merits of doing something illegally? AndyTheGrump (talk) 20:13, 8 October 2012 (UTC)

He didn't say anything about advice. The question itself is descriptive and neutral. --Trovatore (talk) 20:15, 8 October 2012 (UTC)

The 22 GB sounds like the full movie, at the compression level it has on a Blu-Ray disk. 2 GB would require heavy, lossy compression, and would look bad on a 1080p screen, as a result. They might also drop frames, making it look jumpy on any sized screen. StuRat (talk) 20:19, 8 October 2012 (UTC)

Well, it would not look _as good_ on a 1080p screen as a result. The question as to whether it would look _20 gigs worse_ is one most pirates have already answered: no. ¦ Reisio (talk) 20:42, 8 October 2012 (UTC)

It's perhaps worth remembering most legal HD downloads use no where near the bitrate of most BluRay releases so apparently even those responsible don't feel BluRay bitrate is always needed when other considerations come in to play. (And sometimes there isn't even a BluRay release but there is a HD download release, but by nature there are easier to restrict by location possibly requiring a working proxy for whatever geographical location and a foreign credit card to 'purchase' and download. And then there are the releases which were never released on BluRay or HD download but were broadcast in HD and released in DVD or SD download. Both meaning ironically in some locations HD is available to those who obtain stuff by copyright infrigement but not to those who do want to obtain stuff legally either at all or without jumping through many hoops.) Nil Einne (talk) 12:11, 14 October 2012 (UTC)

Most 'rips' are recompressed. It's possible simply special feature or certain audio tracks were removed but this is rarer, generally speaking if it's description as a 'rip' (or particularly 'brrip') by someone who knows what they're talking about, that often means it's recompressed. If it's the original BluRay which hasn't been recompressed etc, it will often be called something like 'untouched' (or possibly BD25/BD50 although these terms may not guarantee it was untouched as they simply refer to what it's suitable to burn to) or 'remux' (although this term could also be used in other cases) depending on what was done to it. You may be able to tell by the size too but you have to be careful. Generally the nfo should make it clear what was done if it's a scene release or a decent releaser. Nil Einne (talk) 03:02, 9 October 2012 (UTC)

Depending on the quality of the encoding, disk content and the number of sound channels, original blu-rays can be anywhere from 5 gigs to 50 gigs (dual layer) large. The merits of mkv can be found at www.matroska.org but afaik it's a far more efficient format than avi and less lossy. Therefore mkv files are large... I've seen them ranging from 4 gigs to 20 gigs. The format is gaining in popularity and is supported by more hardware media players nowadays. Sandman30s (talk) 07:18, 9 October 2012 (UTC)

MKV is simply a container format. It has a minor efficiency advantage with certain codecs and configs over AVI (particularly when it comes to VBR and B frames) and better support for certain things like the aforementioned, as well as multiple video streams and embedded (not hardcoded) subtitles; also for related reasons may have other advantages like when it comes to avoiding audio sync issues, seeking and support (meaning since there's a better defined way of doing that stuff, you don't get a bunch of different implementations which don't always work with different players). However the efficiency of MKV is largely dependent on the codec used since as stated it's simply a container format. MKV could contain lossless video, or as I hinted above the original unreencoded BluRay streams, or something encoded with a high efficiency codec at crappier quality then the lowest Youtube quality (and therefore of comparable low size). Generally speaking, any AVI could be remuxed as an MKV so it doesn't make any sense to talk about quality or size difference when it comes to MKV vs AVI, discounting the minor efficiency advantage except perhaps in regard to scene rules and common practices. Notably the WebM container is basically a subset of the Matroska one, albeit with only one possible video and audio codec, and that of course is one of the options Youtube uses for their HTML5 video support which gives a limited idea of the bitrate/quality variation possible. Nil Einne (talk) 12:31, 9 October 2012 (UTC)

Appliance timers

They generally can turn things on or off every few minutes, but I'm looking for one that can turn things on or off every second, to attach to my microwave oven. Currently, even on the lowest setting, the outside of food burns while the center stays cold. So, I'd like to cook things longer, on a lower average power setting. My current workaround is to turn the microwave on and off manually, waiting in between for the heat to evenly distribute, which isn't very satisfactory. One of those microwave absorbing disks under the center also helps a bit, but not enough. And, yes, I have a manual microwave which is "always on" so long as it has power, time on the manual dial timer, and the door shut. StuRat (talk) 22:59, 8 October 2012 (UTC)

I can hardly imagine a more effective way of destroying electrical equipment than cycling the power every second. Well, bashing it with a hammer, I suppose. Looie496 (talk) 00:59, 9 October 2012 (UTC)

Actually may not be a bad idea. After StuRat spends $50-100 on the 'second' cycling timer and kills their microwave, they can spend $200-300 on a new microwave oven with an inverter/PWM and hopefully not have to complain here again. Nil Einne (talk) 03:08, 9 October 2012 (UTC)

When you turn a microwave to low, that's exactly what it does, it cycles on and off. Unfortunately, 1 second on and 7 off seems to be about the longest cycle, which isn't enough for the heat to redistribute fully. StuRat (talk) 04:42, 9 October 2012 (UTC)

The difference is that when you use the controls, you can be sure that the device has capacitors and stuff to protect itself against any power surges that might result. When you are cycling the external power rapidly, you're putting the device into a situation that it was not designed to handle. Any modern electrical device is designed to handle power fluctuations, but not an extended series of large fast fluctuations like that. It's possible that nothing bad would happen, but it's also possible that you would fry the circuitry. Looie496 (talk) 05:19, 9 October 2012 (UTC)

I'm assuming you have a pretty simple Microwave with mechanical controls, since you can cut the power and reconnect it and have it keep cooking. If you feel like cycling the power won't hurt it, then go ahead. The best cheap solution I can think of is to build something yourself, if you have the skills. For an analog setup you could set up some sort of simple RC delay turn a relay on and off. You could even work in a potentiometer for control. I can't help you much, because I would go the digital way - use a cheap hobbyist microcontroller kit like the Arduino and use it to drive a relay. If you want to look more into prebuilt solutions, "pulse-width modified" is a way to describe an output that acheives an average voltage by turning a constant higher voltage on and off. Usually it applies to things cycling several times a second, but the industrial controllers I have worked with still use the term to describe things that can cycle on the order of several seconds. 209.131.76.183 (talk) 11:29, 9 October 2012 (UTC)

Probably quicker, easier and safer to buy a new microwave oven that works properly. Astronaut (talk) 15:04, 9 October 2012 (UTC)

I agree, but that solution was already given. I figured I could at least point him towards what he wanted. Sturat, I am curious what you're cooking that burns on a 13% duty cycle. I normally only need that low of power for defrosting, and I haven't had anything burn while using it. Maybe there is simple solution to cooking the food that doesn't involve buying a new microwave or modifying your existing one. Also, out of curiosity, how does the power setting work on your microwave? I'm picturing something like several sets of traces on the back of your timer dial, each for a different duty-cycle. If that is the case, you may be able to trim off some of the conductor for the lowest power setting, if you don't mind permanently modifying your microwave. 209.131.76.183 (talk) 16:16, 9 October 2012 (UTC)

Microwaves seem to prefer liquid water over ice, so they can seriously overheat one thawed pocket while leaving the rest frozen. Unless, of course, enough time is allowed for the heat to distribute itself and for everything to thaw. At that point, heating by microwave becomes more even. For boil-in-bag items, I sometimes thaw them first in hot water, but this doesn't work for other items which would get soggy while thawing. StuRat (talk) 23:11, 9 October 2012 (UTC)

An alternative to decreasing the energy output would be to add a container of water to absorb some of that energy, thus decreasing the amount absorbed by the food item. Be sure to include a wooden spoon or popsicle stick to encourage boiling and avoid superheating should the water get that hot. -- Tom N (tcncv) talk/contrib 22:57, 9 October 2012 (UTC)

That's a good idea, and nice use of a previous Ref Desk Q regarding the wooden spoon. StuRat (talk) 23:08, 9 October 2012 (UTC)

I know this sounds weird, but try putting the food not in the middle of the microwave but to the side. They (talk) 22:46, 11 October 2012 (UTC)

Presumably more microwaves are aimed at the center than the sides of the microwave, so that wouldn't help. I do sometimes do that, though, say if I have one end hot and the other end frozen. I try to position the frozen end towards the center and the hot end near the edge. StuRat (talk) 00:26, 14 October 2012 (UTC)

The reason why it's recommended to place things at the side is because the turntable is ineffective in the centre as it doesn't move the food around so may have the problem of parts of the food being in continous 'hot' spots (peaks of a standing wave) and others in continous 'cold' spots, this was also discussed on the RD before BTW. Or to put it a different way, there is a reason why most microwaves have turntables and if you're putting food in the centre you may be barely using them. (It may also depend on your microwave even if it does have a turnable [1].) Of course if you are using the microwave at non full power, it's possible that the turntable frequency and on and off frequency may be in sync meaning it may not matter where you put the food, I'm not sure whether this is always taken in to account. In any case, clearly the moving around is likely to be less effective when you use a microwave which achieves lower powers by turning it on and off seconds apart. Another reason why a microwave with an inverter may make sense. I don't believe it's generally correct that more microwaves are aimed at the centre BTW, in fact I think the results of those experiment aimed at measuring the speed of light, or the microwave wavelength or whatever or just a demonstrating the aforemention issue with food in the centre demonstrates that. E.g. [2] [3] [4] [5] [6] [7]. In fact from those results I'm not sure whether the centre is even always the location of a peak/hot spot, it may commonly be but not always. Nil Einne (talk) 12:03, 14 October 2012 (UTC)

I reasoned that they would design them that way, to minimize the effect of the center of frozen foods remaining frozen while the edges burn. StuRat (talk) 08:27, 15 October 2012 (UTC)

The notion that it's recommended to place things at the side is because the turntable is ineffective in the centre as it doesn't move the food around is valid only if the axis isn't occupied if "things" are placed at the side. As long as the food is not off axis, shifting the food on the turntable will only "move" the axis within the food, which may be detrimental IF a peak is on the axis and the axis is near the edge of the food item.

However, (OR/wild guess) it would make sense to place the peaks off-axis when designing a microwave oven, as having a strong peak at the axis would defeat the purpose of a turntable. From the frequency (2.45Hz) and the speed of light (~3e8m/s) one gets a half-wavelength of ~6.1cm, and that should be the order of magnitude of a strong peak. Where the peak is will probably be hard to compute, and I wouldn't be surprised if designers worked out a new oven by applying a crude 1D model (say, make the oven a multiple of 6.1cm wide) and then try different heights and emitter placements until they're satisfied with the wave distribution.

I looked at my turntable, and it is mounted slightly (~1.5cm) off-center, so I'd guess the main peak will be off-axis by that amount, and neither a peak nor a node will be on the axis.

p.s. Not sure what this has to do with computing anyway... - ¡Ouch! (^{hurt me} / _{more pain}) 07:03, 17 October 2012 (UTC)

It's a terrible idea without knowing the details of how the high-voltage electronics and magnetron will interact with a triac on the supply circuit, but I am curious what would happen if you plugged the microwave into one of your new dimmer switches. :-) Of course, don't try it unless you don't mind breakings things and don't mind buying a new microwave/dimmer/countertop. 209.131.76.183 (talk) 13:46, 17 October 2012 (UTC)

I'm already aware that reducing the voltage to the magnetron is not a good idea. If it were, then that's how microwave ovens would vary the power level. They keep turning it on and off precisely to get around that problem. StuRat (talk) 21:00, 17 October 2012 (UTC)