CVS: main/DOCS/xml/en encoding-guide.xml,1.32,1.33
CVS change done by Guillaume Poirier CVS Update of /cvsroot/mplayer/main/DOCS/xml/en In directory mail:/var2/tmp/cvs-serv16251/DOCS/xml/en Modified Files: encoding-guide.xml Log Message: Add indicative QP for ASP and AVC codecs Index: encoding-guide.xml =================================================================== RCS file: /cvsroot/mplayer/main/DOCS/xml/en/encoding-guide.xml,v retrieving revision 1.32 retrieving revision 1.33 diff -u -r1.32 -r1.33 --- encoding-guide.xml 20 Oct 2005 13:45:41 -0000 1.32 +++ encoding-guide.xml 27 Nov 2005 19:48:39 -0000 1.33 @@ -1043,6 +1043,9 @@ <sect3 id="menc-feat-dvd-mpeg4-resolution-bitrate-compute"> <title>Computing the resolution</title> <para> + The following steps will guide you to compute the resolution of your + encode without taking too much distortion by taking into account several + information about the souce video. First, you should compute the encoded aspect ratio: <systemitem>ARc = (Wc x (ARa / PRdvd )) / Hc</systemitem> <itemizedlist> @@ -1079,17 +1082,30 @@ </para> <para> - The CQ depends both on the bitrate and the movie resolution. + The CQ depends both on the bitrate, the video codec efficiency and the + movie resolution. In order to raise the CQ, typically you would downscale the movie given that the bitrate is computed in function of the target size and the length of the movie, which are constant. - A CQ below 0.18 usually ends up in a very blocky picture, because there + With MPEG-4 ASP codecs such as <systemitem class="library">XviD</systemitem> + and <systemitem class="library">libavcodec</systemitem>, a CQ below 0.18 + usually ends up in a pretty blocky picture, because there are not enough bits to code the information of each macroblock (MPEG4, like many other codecs, groups pixels by blocks of several pixels to compress the image; if there are not enough bits, the edges of those blocks are visible). It is therefore wise to take a CQ ranging from 0.20 to 0.22 for a 1 CD rip, - and 0.26-0.28 for 2 CDs. + and 0.26-0.28 for 2 CDs with standard encoding options. + More advanced encoding options such as those listed here for + <link linkend="menc-feat-mpeg4-lavc-example-settings"><systemitem class="library">libavcodec</systemitem></link> + and +<link linkend="menc-feat-xvid-example-settings"><systemitem class="library">XviD</systemitem></link> + should make it possible to get the same quality with CQ ranging from + 0.18 to 0.20 for 1 CD rip, and 0.24-0.26 for 2 CDs + With MPEG-4 ASP codecs such as <systemitem class="library">x264</systemitem>, + you can use a CQ ranging from 0.14 to 0.16 with standard encoding options, + and should be able to go as low as 0.10 to 0.12 with + <link linkend="menc-feat-x264-example-settings"><systemitem class="library">x264</systemitem>'s advanced encoding settings</link>. </para> <para> @@ -1098,6 +1114,8 @@ to a movie such as The Matrix, which contains many high-motion scenes. On the other hand, it is worthless to raise CQ higher than 0.30 as you would be wasting bits without any noticeable quality gain. + Also note that as said earlier on this quide, low resolution comparatively + need a bigger QP to look good. </para> </sect3>
On Sun, 27 Nov 2005, Guillaume Poirier CVS wrote:
Index: encoding-guide.xml
<para> @@ -1098,6 +1114,8 @@ to a movie such as The Matrix, which contains many high-motion scenes. On the other hand, it is worthless to raise CQ higher than 0.30 as you would be wasting bits without any noticeable quality gain. + Also note that as said earlier on this quide, low resolution comparatively + need a bigger QP to look good. </para> </sect3>
Shouldn't that be bigger CQ / smaller QP? --Loren Merritt
On 11/27/2005 02:48 PM, Guillaume Poirier CVS wrote:
CVS change done by Guillaume Poirier CVS
+ The following steps will guide you to compute the resolution of your + encode without taking too much distortion by taking into account several + information about the souce video.
"to compute" -> "in computing", but while the result would be mostly grammatical I'm not sure it would be clear. I think what you mean is "without distorting the video too much" (i.e., without losing much quality), but the current phrasing does not seem to say that, and I'm not entirely sure what would be a good fix. Also, the double use of the word "taking" in close proximity is not a very good thing.
<para> - The CQ depends both on the bitrate and the movie resolution. + The CQ depends both on the bitrate, the video codec efficiency and the + movie resolution.
Since you're no longer talking about just two things, you want "depends on all of" or just "depends on".
In order to raise the CQ, typically you would downscale the movie given that the bitrate is computed in function of the target size and the length of the movie, which are constant. - A CQ below 0.18 usually ends up in a very blocky picture, because there + With MPEG-4 ASP codecs such as <systemitem class="library">XviD</systemitem> + and <systemitem class="library">libavcodec</systemitem>, a CQ below 0.18 + usually ends up in a pretty blocky picture, because there
"ends up" -> "results" (I'm thinking that I might need to go over this file and see what I can fix, just on my own.)
are not enough bits to code the information of each macroblock (MPEG4, like many other codecs, groups pixels by blocks of several pixels to compress the image; if there are not enough bits, the edges of those blocks are visible).
I'd add a period after "macroblock" and move the existing period back one character, making the entire parenthetical comment its own (still parenthetical) sentence. This is, of course, unrelated to your change.
It is therefore wise to take a CQ ranging from 0.20 to 0.22 for a 1 CD rip, - and 0.26-0.28 for 2 CDs. + and 0.26-0.28 for 2 CDs with standard encoding options. + More advanced encoding options such as those listed here for + <link linkend="menc-feat-mpeg4-lavc-example-settings"><systemitem class="library">libavcodec</systemitem></link> + and +<link linkend="menc-feat-xvid-example-settings"><systemitem class="library">XviD</systemitem></link> + should make it possible to get the same quality with CQ ranging from + 0.18 to 0.20 for 1 CD rip, and 0.24-0.26 for 2 CDs
"a 1 CD rip" or "1 CD rips" or even just "1 CD" - for both correct plurality and, in some cases, parallelism with the "two" case.
On the other hand, it is worthless to raise CQ higher than 0.30 as you would be wasting bits without any noticeable quality gain. + Also note that as said earlier on this quide, low resolution comparatively + need a bigger QP to look good.
"as said earlier on" -> "as mentioned earlier in" (or even "as described earlier in") ...actually, there's something wrong with the entire sentence. There's something strange about the tense of "need", and I'm not sure what is meant here by "comparatively" at all - comparatively low resolution? comparatively high QP? something else which I'm not quite finding words for? -- The Wanderer Warning: Simply because I argue an issue does not mean I agree with any side of it. Secrecy is the beginning of tyranny.
On Sun, Nov 27, 2005 at 06:23:10PM -0500, The Wanderer wrote:
(I'm thinking that I might need to go over this file and see what I can fix, just on my own.)
Go for it, and don't hold back :) Diego
Diego Biurrun wrote:
On Sun, Nov 27, 2005 at 06:23:10PM -0500, The Wanderer wrote:
(I'm thinking that I might need to go over this file and see what I can fix, just on my own.)
Go for it, and don't hold back :)
Thanks for reminding me - I was thinking of this earlier today and couldn't remember which file I'd said it about. I'm probably not going to get to it this evening, but it's a good candidate for the morrow. -- The Wanderer Warning: Simply because I argue an issue does not mean I agree with any side of it. Secrecy is the beginning of tyranny.
participants (4)
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Diego Biurrun -
Loren Merritt -
syncmail＠mplayerhq.hu -
The Wanderer