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| Encoding Tutorial; The most confusing part | |
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| Tweet Topic Started: Aug 6 2009, 03:33 PM (1,599 Views) | |
| JinK | Aug 6 2009, 03:33 PM Post #1 |
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Basic Concept When one sees a video, they expect many things. One would expect the video to be clean with crisp edges and nice blending of colors. One would expect the video to play smoothly and without lag. One would expect the video and audio to be in synch. One would expect the video to be a good size for its quality given. One would expect the video to play correctly on their computer. All of these troubles depend on the encoder. To do all this is not one easy job. It requires a GREAT wealth of knowledge (as well as trial and error) to get the perfect outcome… a delicate balance between file size and quality. Many others explain videos from the basics to the specific details. In this tutorial, the fine details shall be explained first because if one wants to encode videos, an encoder must know these details. Compression As many know, an anime uncompressed takes a ridiculous amount of space; approximately 4 GB of data in a single minute in a 1280x720 video. Because of this, videos are compressed for the sake of saving space so that one can store more of those precious videos. That single minute that was 4 GB can be compressed down to a mere 20MB (that’s about 1/200ths the uncompressed size) and still retain its video and audio quality. Animes, as of late, have been compressed down to standard sizes of 175MB, 200MB, 230MB, 270MB, 300MB, 330MB, or 350MB for its ability to fit in CDs and DVDs and not because it’s an ideal size of a balance between quality and size. A video can be compressed in many, many methods. Compressing a video is quite the headache for anybody that doesn’t know anything about encoding. First of all, there are many different ways to compress videos. The reason why there are so many compression methods is because each compression method takes more or less CPU power or takes more or less space. Therefore, certain compression methods are used for different purposes (examples: streaming, archival, one-time-viewing, professional editing, etc.). These different ways of compressing videos are where codecs come in. Video codecs either encode for when you want to make into a different compression format or to change the compression level, or decode videos for when you wanna see video (You may notice that trays on the taskbar on the bottom right appear when you watch videos). Codecs basically allow one to read or write with different compression methods of videos. You may already know a few compression methods (H.264, divX, Xvid, rm, rmvb, mpeg, mp3, pcm, gsm, etc). For the sake of common understanding, to explain the image portion of a video, the word video shall be used and audio for the sound portion of a video from now-on-forth. Edited by JinK, Aug 6 2009, 07:17 PM.
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| JinK | Aug 6 2009, 03:38 PM Post #2 |
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Video Compression Videos take a tremendously large portion of space. By compressing data, unneeded data gets thrown away. What kinds of data get thrown away? Well…for instance, when there is a still background, it’s unnecessary for the one to store the same data over and over again for each frame the background is there. Or in another situation, a moving object doesn’t change how it looks and merely moves around. One has to make sure that the video encoded is done well. There are many factors to which make a video good or bad. The two pictures below are from videos encoded to the same file size yet the outcome was drastically different. Posted Image Posted Image Video compression is very complex and is still advancing. And it's necessary to know all those little things. There are two different types of video compression: lossy and lossless. As its name suggests, lossy video loses picture quality and lossless video retains all of the original video’s quality. However nice lossless sounds, it is largely not preferred as the video still is huge. Lossy video is what this tutorial shall cover. There are multiple compression methods. Compressing a video will require more than just general knowledge of compression formats. For the sake of simplicity, this tutorial shall talk specifically about mpeg-2, mpeg-4, divX, Xvid, and h.264 out of the countless others that there are.
Video Standards There were 3 video standards that were developed for the sake of broadcast television. Those three would be National Television System Committee(NTSC), Phase Alternating Line (PAL), and Séquentiel couleur avec mémoire (SECAM). NTSC and PAL the more commonly used systems. Although these were originally for analog systems and actually refer to color encoding and such into broadcast waves, these systems are now used mostly to identify standards of frame rate and frame size in digital videos, which are now much more popular. Currently, a new system is being developed, known as ATSC. This system will be used to broadcast high definition.
Video bitrates Bitrates are basically the amount of video information that the video gives out per second. You can find the average bitrate of a video by getting the size of the video and dividing the size in Kb(kilobits) by the number of seconds. You can find the size in kilobits by getting the size of the video in MB, multiplying that by 1024 to get kilobytes and then multiplying the kilobytes by 8 to get kilobits. Increasing the bitrate doesn’t necessarily always make the quality better, but it does increase the possibility of higher quality. However, higher bitrates mean higher file size, too. It's wise to have a Variable Bit Rate(VBR) than a Constant Bit Rate(CBR) as some parts of video are simple compared to other parts and thus you can save space by lowering the Bit Rate. Motion estimation(ME) Motion estimation compares macroblocks of a previous frame to macroblocks of the current frame.
Quantization Quantization is the most complex part of video compressing. This requires advanced knowledge and isn’t something a novice would want to try to mess with. Although, one may want to play around to try to find the perfect balance as quantization is something that directly effects the video quality, in a large way.
Encoding modes
Other Stuff
Edited by JinK, Apr 28 2013, 04:37 PM.
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| JinK | Aug 6 2009, 03:45 PM Post #3 |
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Audio Compression There are multiple compression methods. Compressing a video will require more than just general knowledge of compression formats. For the sake of simplicity, this tutorial shall talk specifically about mp3, **TO BE EDITED** out of the countless others that there are. mp3 – **TO BE EDITED** Audio Sample Rates 8000Hz, 11025Hz, 16000Hz, 22050Hz, 44100Hz, 48000Hz **TO BE EDITED** Audio bitrates Just like for the video, bitrates for audio are basically the amount of audio data that’s given out per second. You can find the average bitrate of an audio by getting the total size of audio in kilobits and dividing it by the total time. You can find the kilobits by getting the size in MB and multiplying by 1024 to get Kilobytes and then further multiplying by 8 to get Kilobits. 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 and 384kbps are standard bitrates for audio. Channel Encoding
Other Stuff **TO BE EDITED** Edited by JinK, Aug 6 2009, 09:43 PM.
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| JinK | Aug 6 2009, 03:47 PM Post #4 |
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Putting it all together This is the part where most people are familiar with and also the easy part. First, you need a container. A container holds the video and audio in a format to be read. Some formats include mp4, mkv, ogg, ogm, rmvb, rm, avi, flv, wmv, mpg, mp4, and etc. Not all containers are compatible with all video/audio compression formats. Although there are countless formats, this tutorial shall concentrate on 3 formats: avi, mkv, and mp4
Programs Virtual Dub – **TO BE EDITED** Media Coder – **TO BE EDITED** AviDemux – **TO BE EDITED** MeGUI – **TO BE EDITED** Sony Vegas – **TO BE EDITED** MP4Muxer – **TO BE EDITED** Edited by JinK, Feb 27 2010, 10:23 PM.
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