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    <p>It will vary dramatically depending on the content of the source videos. I'll get to that in a bit. </p> <p>640x360 is not that large. 512kbps is very reasonable and arguably standard. Maybe 768kbps if you are really interested in quality.</p> <p>How is this possible? A simplified answer: There are a couple of techniques and facts about <a href="http://en.wikipedia.org/wiki/Video_compression" rel="noreferrer">video compression</a> that make this possible: </p> <ol> <li><strong>Not every video frame</strong> data structure in an common H.264 (or other CODECs for that matter) <strong>is a full image</strong>. Instead there are two types which are colloquially referred to as <ol> <li><strong>Key Frames</strong>: a full rendering of the entire video image</li> <li><strong>Intra-frames</strong>: a description of changes to the previous frame. These frames generally make up the vast majority (80%-99%) of frames in a video.</li> </ol></li> <li><strong>H.264 is "<em>lossy</em>"</strong>, as are many other CODECs. They do not reproduce a pixel-by-pixel, frame-by-frame exact duplicate of the original source video. <strong><em>Example</em></strong>: Lossy blocks: If all but one pixel in an area is the same color, the CODEC 'loses' the one pixel. So, instead of having to store information about every single pixel in a frame, the CODEC just says <em>"x1, y1 to x2, y2 are all color x"</em>. Very efficient. </li> </ol> <p>It is all wildly more complex than that, with zillions of different approaches, techniques and algorithms within specific CODECs and between CODECs to make this happen.</p> <p>So, back to the "It will vary dramatically depending on the content of the source videos" comment: The compression ratio you'll see, and the resulting quality, will depend significantly upon:</p> <ul> <li>the contents of the video</li> <li>your tolerance for artifacts (blocks, loss of color, loss of definition)</li> <li>the CODEC parameters you set, and how you set them</li> </ul> <p><strong><em>Example</strong>: A video of a door in a room (like a security camera) with one key frame every ten minutes is going to have an amazingly high compression ratio. My back-of-the-napkin calculations put that scenario at 15,000:1 compression.</em></p> <p>Since you are starting on a large video encoding project, I would recommend a couple of things to determine what your compression ratio is going to be:</p> <ul> <li>take a sample of the source videos you are going to encode. 100 or more being statistically relevant.</li> <li>encode them at various bit rates, with various parameters, to determine what resulting characteristics meets your needs</li> </ul> <p>Changing the parameters of the encoder to make the videos smaller can have other impacts too:</p> <ul> <li>higher play back CPU requirements</li> <li>player CODEC expectations. Not all H.264 encoded videos can be played back by all players</li> <li>longer encoding times</li> <li>various degrading of quality</li> </ul> <p>It's a big complicated subject. Good luck. My experienced <em>"thumb-to-the-wind"</em> test says you'll be more than happy with 512-768kbps for your project.</p>
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    1. POSuggested Compression Ratio with H.264?
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    1. USStu Thompson
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    1. COStu, thanks for the detailed response. I've been waiting for a while for some answers to this question. Really helpful to get a concise guide to what I should be researching further. It's amazing how efficient H.264 seems to be...
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