Videomaker – Learn video production and editing, camera reviews › Forums › General › Video and Film Discussion › miniDV Quality to DVD › There will always be some
There will always be some quality loss when encodingfor DVD. (even if you can’t notice it)
DVD footage needs to be mpeg2which is a lossy format, but it shouldn’t look bad if its encoded properly.
Thethree general formats are:
1 PASS CBR:
This is for shorter videos that have a minimal amount of fast action movements and/or pans Thisisthe faster method of encoding and will render a larger file.typically the best bit rate will be 8mbps, but 7mbps is good too. You can go higher but this is not recommended becauseit may be to fast for some DVD players.
1 PASS VBR
This setting may not be available with many encoders and really isn’t necessary, but it would typically be used with longer videos with a minimal amount of fast movement.
2 pass VBR
This is used for longer videos that include fast action movement. It will analylze the video in the first pass and than encode a higher bit rate for parts of the video that have fast action and lower bitrates in the areas that have less movement. This format maximizes quality while maintaing a smaller file size. The bitrate will depend on how long your video is. In variable bitrate encoding, there are3 settings:
-Average Bitrate-Maximum Bit Rate – Minimum Bitrate
The range between 6.5 -8.0 mbps will renderbetter quality, however, if you video is over 90 minutes, you’ll have to use a lower range.
I have noticed that motion graphics and animated backgrounds seem to be more affected by DVD compression, so if this describes your video, expect there to me some undesireable effects. There really is not too much you can do…DVD compression was great for awhile, especially when there wereonly tube TVs. The moitors today are very detailed and show off all the imperfections.
If you have aGood HD monitor, you’ll notice that any Hollywood Blockester on DVD has some artifacts in the motion graphic intros…and in some cases, it’s really bad…including text. You’ll also notice some artifacts in thedarker scenes of the movie as well. But sometimes, you really can’t tell unless you’re looking for it.
It also may help to do a search for a good Bit Rate calculator. This may make it a little easier for you to determine the settings for VBR. If you don’t like the quality using the settings that the bit rate calculator gave you, try using a higher rate if you video didn’t max out the space on the DVD.
Its not necessary to know this, but you may see settings for GOP(groups of pictures). You can usually keep this at the default setting. GOPis the compression techniquethat givesDVD compression its lossy characteristic. Thaey consist of I-frames B-frames and P-frames.
I found this following explanation fromwikipedia to be rather humorous the fist time I read it:
MPEG-2 specifies that the raw frames be compressed into three kinds of frames: intra-coded frames (I-frame), predictive-coded frames (P-frames), and bidirectionally-predictive-coded frames (B-frames).
An I-frame is a compressed version of a single uncompressed (raw) frame. It takes advantage of spatial redundancy and of the inability of the eye to detect certain changes in the image. Unlike P-frames and B-frames, I-frames do not depend on data in the preceding or the following frames. Briefly, the raw frame is divided into 8 pixel by 8 pixel blocks. The data in each block is transformed by a discrete cosine transform. The result is an 8 by 8 matrix of coefficients. The transform converts spatial variations into frequency variations, but it does not change the information in the block; the original block can be recreated exactly by applying the inverse cosine transform. The advantage of doing this is that the image can now be simplified by quantizing the coefficients. Many of the coefficients, usually the higher frequency components, will then be zero. The penalty of this step is the loss of some subtle distinctions in brightness and color. If one applies the inverse transform to the matrix after it is quantized, one gets an image that looks very similar to the original image but that is not quite as nuanced. Next, the quantized coefficient matrix is itself compressed. Typically, one corner of the quantized matrix is filled with zeros. By starting in the opposite corner of the matrix, then zigzagging through the matrix to combine the coefficients into a string, then substituting run-length codes for consecutive zeros in that string, and then applying Huffman coding to that result, one reduces the matrix to a smaller array of numbers. It is this array that is broadcast or that is put on DVDs. In the receiver or the player, the whole process is reversed, enabling the receiver to reconstruct, to a close approximation, the original frame.
Typically, every 15th frame or so is made into an I-frame. P-frames and B-frames might follow an I-frame like this, IBBPBBPBBPBB(I), to form a Group Of Pictures (GOP); however, the standard is flexible about this.