Thanks Jesse - I mean, I know what compression is, what codecs are, how you only want to compress once, etc... but the rest of the details you sent are very useful - thanks. Do I owe you for that? That was better than Moses!
Jason Merrill | E-Learning Solutions | icfconsulting.com >>-----Original Message----- >>From: [EMAIL PROTECTED] [mailto:flashcoders- >>[EMAIL PROTECTED] On Behalf Of JesterXL >>Sent: Monday, November 21, 2005 3:52 PM >>To: Flashcoders mailing list >>Subject: Re: [Flashcoders] Flash 8 grossly inflates .flv file? >> >>Codecs, standing for "compression/decompression" are mathematical algorithms >>to shrink overall filesize of assets. There are codecs for both video & >>audio. Some image form compression algorithms translate to video, others do >>not, since video is just a bunch of images stitched together. >> >>RAW video, usually, is a series of images & audio. Depending on format, >>they can be independent entities (like Quicktime's "tracks"), or just called >>tracks, but really a mesh (like MPEG for example). Usually, even RAW video >>is broken down into mJPEG (motion jpeg) to be more managable since although >>mJPEG is a lossy codec, at such a high setting (like 90), the video still >>looks good, but drops significantly in filesize. >> >>Codecs, like image formats, come in 2 flavors: lossy and lossless. Lossy >>compression means you lose image quality when using the codec. JPEG does >>this by removing colors the human eye cannot see (nor can a lot of computer >>video monitors render). Most go farther depending on how low you set the >>quality level. Bottom line, the more you compress something with a lossy >>codec, the more image degradation will occur and overall, it becomes to look >>worse and worse (pixelated, blurry, smudged, weird colors). >> >>Lossless codecs, like PNG, do not negitively affect the image quality in >>anyway, they mere use common mathetical algorithms to shrink the filesize of >>each frame. Lossless, however, have a set value, are usually not too >>configurable, and you have little to no control over "how compressed" >>something gets. >> >>Lossy codecs use 2 basic methods to compress video. Frame compression and >>time-lapse compression. >> >>Most codecs use something called a keyframe. There are other types of >>frames too, but the point is, you take a point in the video, a frame that is >>pretty high quality, and then save the information. So, for a talking head >>video for instance, they'll compress the backround more because if it's all >>1 color, say bluescreened or white, it's really easy to not only use >>losslesss compression (like GIF where it uses lzw and turns a ton of white >>pixels it 1 white pixel). >> >>Timelapse, they'll use that 1 keyframe as a guide to how to compress the >>rest of the frames, say the next 30. If it's a person talking, usually only >>parts of the face change, while the rest doesn't, so there is little point >>in redrawing each of the other frames if the face doesn't change. >>Additionally, you don't even need to store pixel information about those >>frmaes if you are just redrawing really small parts. >> >>There are other types of frames used in different codecs, but those are the >>basic 2. >> >>Spark & On2 are both lossy codecs. As such, you can control the level of >>compression (usually by the datarate, or how much kilobytes is used per >>second). So, if you have 30 frames per second, you'll effectively have 700k >>to distribute amongst 30 small images, assuming you go with On2's highest, >>default datarate. You can quickly see how lowering framerate of video >>drastically increases quality since going from 30 to 15 frames per second >>doubles the amount of kilobtyes each frame gets to use. >> >>...obvoiusly, audio usually uses mp3. >> >>Now, re-compression of compressed video usually screws this up on a number >>of levels, resulting in worse looking video, and higher filesizes. 2 main >>reasons for this. >> >>First off, the video already looks bad. No video codec in the world makes >>something look BETTER after you'ev used it, even lossless. You are losing >>infromation somewhere, and with lossy, you can be sure image quality will >>degrade. If you do it again, you are degrading something that is already >>degraded, thus degrading it more. What does that mean? You took something >>that looked bad and made it worse. >> >>Secondly, codecs are designed to find common light and color patterns in >>video and compress based on those. The pixels that are left over via >>redraw, as well as the blurring of color, and added noise to the compressed >>video not only confuses the codec, but gives it less information to work >>with. >> >>Go take a JPEG that';s comprssed to 50 percent, and then compress it again, >>and you'll see how both visually it looks like crap, and filesize doesn';t >>improve. >> >>It is common in the video world, however, to not save the source. Since >>uncomprssed video, even using mJPEG to compress it once still takes up gigs >>and gigs of space (usually a hard drive or two), you can't just "have it >>around" unless you work in the video industry and have the space for such >>things (like DV tapes, DVD-ROM storage devices, huge RAIDs, etc.). >> >> >> >> >>----- Original Message ----- >>From: "Merrill, Jason" <[EMAIL PROTECTED]> >>To: "Flashcoders mailing list" <[email protected]> >>Sent: Monday, November 21, 2005 3:15 PM >>Subject: RE: [Flashcoders] Flash 8 grossly inflates .flv file? >> >> >>Yeah, I think I will just tell them to bite me. Not really, but >>something like that. >> >>Is this true of any video editing software? - that compressed WMV files >>get inflated when you try and convert them to another format because the >>codec freaks out - or is it just an anomaly/bug with Flash 8 and/or the >>available codecs? >> >>Jason Merrill | E-Learning Solutions | icfconsulting.com >> >> >> >> >> >>>>-----Original Message----- >>>>From: [EMAIL PROTECTED] [mailto:flashcoders- >>>>[EMAIL PROTECTED] On Behalf Of JesterXL >>>>Sent: Monday, November 21, 2005 3:11 PM >>>>To: Flashcoders mailing list >>>>Subject: Re: [Flashcoders] Flash 8 grossly inflates .flv file? >>>> >>>>No one ever does it seems. You're best bet is to use Spark then, >>although, >>>>the size will still be unnacceptable. >>NOTICE: >>This message is for the designated recipient only and may contain privileged >>or confidential information. If you have received it in error, please notify >>the sender immediately and delete the original. Any other use of this e-mail >>by you is prohibited. >>_______________________________________________ >>Flashcoders mailing list >>[email protected] >>http://chattyfig.figleaf.com/mailman/listinfo/flashcoders >> >>_______________________________________________ >>Flashcoders mailing list >>[email protected] >>http://chattyfig.figleaf.com/mailman/listinfo/flashcoders _______________________________________________ Flashcoders mailing list [email protected] http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
