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Codecs and Colour Sampling
Notes on Video Codecs
CODECS
What is a video Codec: "A video codec is a device or software that enables video compression and/or decompression for digital video. The compression usually employs lossy data compression.
There is a complex balance between the video quality, the quantity of the data needed to represent it (also known as the bit rate), the complexity of the encoding and decoding algorithms, robustness to data losses and errors, ease of editing, random access, the state of the art of compression algorithm design, end-to-end delay, and a number of other factors.
(Adapted from Wikipedia0
What three general types of CODECS have we discussed
-Codec for image capture
-Codec for post production, sometimes called an "Intermediate" codec, such as ProRes 422.
-Codec for playback or distribution, such as H264 or Mpeg 4 used for High definition video (which can be rendered in the .mov format)
-If you look on p. 128 of the manual for the HG 21 Vixia Canon camera you are using in class, you will see it describes the Recording Sysem as: Movies: AVCHD, Video compression MPEG-4 AVC/H.26. AVCHD is the tapeless format and MPEG-4 is therecording compression, and you can read more about it here: http://en.wikipedia.org/wiki/AVCHD.http://en.wikipedia.org/wiki/AVCHD.
When you bring the files into Final Cut they are automatically transcoded into ProRes 422 for editing.
Where can you see what the codec of your clips is?
A: in your browser,the information to the right of each clip.
Where/How can you change the codec of your timeline?
A: Under Sequece Settings
What distinguishes Apple Prores 422 (the codec you are using to edit) :
ProRes 422 uses a full 10-bit 4:2:2 color space, which provides much better color fidelity than 8-bit color. This makes a real difference when color grading and compositing images. There is simply more color data to work with, and that can eliminate color banding issues by providing more steps in color gradients.
ProRes 422 uses a variable bit-rate compression scheme in which complex scenes are less compressed than basic or static scenes, so the quality is distributed as needed to maximize the efficiency of the codec for the best possible image. For 1080i, the ProRes 422 data rate is 145Mbps, and there’s also an HQ setting with a 220Mbps rate.
Compared to uncompressed HD video, ProRes files are about five times smaller, using about 20% as much hard drive space per hour. This means smaller, less expensive storage systems can be utilized, making broadcast-quality HD video production more affordable to smaller production houses and independent video producers. ProRes 422 HD video files are so efficient they can be captured and edited on a Mac Book Pro, something you wouldn’t try with uncompressed HD!
There are other HD codecs with lower data rates available, but because they are more highly compressed, they take more processing power to encode and decode (play back). The ProRes 422 codec provides a good middle-ground by providing a smaller file size than uncompressed, while providing easy capture and playback on even marginal machines.
But what about quality? Review after review by video professionals have consistently rated ProRes 422 quality as "visually equivalent" and "undistinguishable" from uncompressed footage, even after multiple encode/decode cycles. This can’t be said about many other compressed codecs available today.
From: http://www.sharbor.com/tutorials/1669.html
-When to use Prores 422, if you have shot in HDV and have a large project. You will likely encounter problems editing and it would be good to switch to Prores 422 or Apple Intermediate codec.
-If your project includes more than one format --both DV and HDV material for example--then you'll need to set your FCP sequence codec to ProRes 422.
From: http://www.mediastorm.com/blog/?p=2442 |
Colour Sampling
Video Colour Sampling (Chroma Sampling)
Color sampling effects how much gradation you have in each color. A camera like Canon’s new XF300 offers 4:2:2 color sampling. That’s twice that of cameras using 4:2:0 sampling, which is most of the competition.
http://www.hdcamreview.com/bitrate.html
The first number in the three number expression is "4" as this represents the luma (or brightness) component, and the next two represent the colour.
The Canon Vixia HG21 which you have been using shoots in AVCHD and AVCHD (Like HDV) video uses the 4:2:0 sampling format, which is superior to the 4:1:1 used in DV camcorders.
http://digitalcontentproducer.com/hdhdv/depth/avchd_compression_070907/
More technical explanations of Colour Sampling
a fuller explanation: http://www.dvxuser.com/articles/colorspace/
and here: http://www.larryjordan.biz/articles/lj_sampling.html
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