video quality ( bit rates )

[fares_poka]

<p>Hello, <br>

I read a lot of articles about bit rates and the compression that the camera does<br>

<br>

Hers my questions<br>

<br>

1/ how does the camera, compress the video? Andwhy? How to control it?<br>

<br>

2/ what are the best settings to achieve the best video quality? <br>

I have a canon 600 d with an SD card (64G) with a speed of 95m/s (u1 )<br>

<br>

3/ is there any good source to learn about this subject? And understanding codecs?</p>

[brett_w.]

<p>you might get more answers in the <strong>video</strong> section here or at a DSLR video section like<br>

http://photography-on-the.net/forum/forumdisplay.php?s=8784c168bb81dd581dcf10f0d71958b8&f=131<br>

or http://www.dpreview.com/forums/1045</p>

<p>also, if you shoot a lot of video the free magic lantern software (installed on the camera) is useful http://www.magiclantern.fm/</p>

<p> </p>

[Charles_Webster]

<p>Fares, since you are a beginner with a new camera, you don't need to be too concerned with these issues. In general the camera's compression algorithms are not visible to us as the user and for a beginner make no difference.<br>

Just go shoot stuff, and when you can tell that your stuff isn't perfect or what you wanted, then go do research. Until then, don't worry about it. It'll be fine.<br>

<Chas><br /><br /></p>

[Andrew Garrard]

<p>What Chas said. Wikipedia isn't a bad starting point if you really want to learn about image codecs, but unless you're a software engineer who needs to know about this (I am, and I don't want you to share my pain), I'd not worry. For what it's worth, <a href="http://www.cameralabs.com/reviews/Canon_EOS_600D_Rebel_T3i/movie_mode.shtml">I gather</a> the codec is <a href="http://en.wikipedia.org/wiki/H.264">h.264</a>.<br />

<br />

<i>Why</i> does it compress it? Because if you record video at 1920x1080 resolution and 30 frames per second with no compression, even if you're using 4:2:0 downsampling, you need to record 89MB per second. If you manage that with your card (unlikely - getting close to the maximum rate is hard), you'd still fill it in twelve minutes. There are external systems that can record uncompressed video for later editing, and cameras that can output this over the HDMI output, but you almost definitely don't want them built into a consumer camera. Delivered video is always compressed - quite heavily for most TV streams, extremely heavily over the internet, less so for Blu-ray (although a "high quality" Blu-ray stream might be 40mbits/s, 18 times less than your uncompressed stream). It's the same reason that people use JPEG to store images rather than raw files, except that it's possible to get much better compression out of video at a good quality, because there's usually a lot of similarity between frames.<br />

<br />

As for quality, there's a "movie rec size" menu on the 600D. If you're set to PAL mode (used for TVs in a number of countries, including my native UK), you'll get the ability to record 1920x1080 at 25fps, 1280x720 at 50fps, and the low quality 640x480 mode at 25fps. If you're set to NTSC mode (used in the US, among other places) you get 1920x1080 and 640x480 at 30fps and 1280x720 at 60fps. The higher the frame rate (fps = "frames per second"), the smoother the video - but bear in mind that mains electricity frequency usually matches these numbers, so recording at 60fps in the UK (for example) might make any lights appear to flicker in the recording. 1920x1080 is "full HD" resolution - the resolution of decent HDTVs - but you pay for it here with a reduced frame rate. 1280x720 is the "other" HD standard, and the faster frame rate might mean it's better if you're shooting sports, etc. Both formats are broadcast, depending on the content. There's also a "1920x1080 24fps" mode which is offered because 24 frames per second matches conventional cinema photography, so you'll get "the cinema look". That appears to be the only control you have in the default BIOS - though Magic Lantern might be able to expand on the available options.<br />

<br />

I hope that helps.</p>

[hong_chow]

<p>I am not sure the bit rate you mean is the bit rate for the compressed video. If so, for a good video quality, the bit-rate, compression ratio, frame rate and SNR are critical. The bigger the bit-rate the better the video quality provided that the others parameters are constant. For example, if you record a video for 1080p 30fps, the video quality of a 20Mbps bit rate is better than 5Mbps.<br>

On the other hand the smaller bit rate has a better compression ratio. So this is a question of balance between video quality and compression ratio.<br>

If you want to be serious about the video codec, you may need to read the video standards (eg. H.264, MPEG4, VC1, DIVX, etc. for what is macro-blocks, motion vectors) or you can search over website for "Introduction to video codec".<br>

Hope it can help.</p>

[fares_poka]

<p>wow , that's a lot of information , thank you , really ! and i think that i should focus on the basics before getting deep</p>