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Avoid short forms and libavcodec should not the that much singled out
git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@16179 b3059339-0415-0410-9bf9-f77b7e298cf2
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@ -292,7 +292,8 @@
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<note><title>Note:</title>
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<para>
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Most codecs which support ABR encode only support two pass encode
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while some others such as <systemitem class="library">x264</systemitem>
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while some others such as <systemitem class="library">x264</systemitem>,
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<systemitem class="library">XviD</systemitem>
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and <systemitem class="library">libavcodec</systemitem> support
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multipass, which slightly improves quality at each pass,
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yet this improvement is no longer measurable nor noticeable after the
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@ -303,28 +304,31 @@
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</note>
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<para>
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In each of these modes, <systemitem class="library">libavcodec</systemitem>
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In each of these modes, the video codec (such as
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<systemitem class="library">libavcodec</systemitem>)
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breaks the video frame into 16x16 pixel macroblocks and then applies a
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quantizer to each macroblock. The lower the quantizer, the better the
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quality and higher the bitrate. The method
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<systemitem class="library">libavcodec</systemitem> uses to determine
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quality and higher the bitrate.
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The method the movie encoder uses to determine
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which quantizer to use for a given macroblock varies and is highly
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tunable. (This is an extreme over-simplification of the actual
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process, but the basic concept is useful to understand.)
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</para>
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<para>
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When you specify a constant bitrate, <systemitem
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class="library">libavcodec</systemitem> will encode the video, discarding
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When you specify a constant bitrate, the video codec will encode the video,
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discarding
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detail as much as necessary and as little as possible in order to remain
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lower than the given bitrate. If you truly do not care about file size,
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you could as well use CBR and specify a bitrate of infinity. (In
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practice, this means a value high enough so that it poses no limit, like
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10000Kbit.) With no real restriction on bitrate, the result is that
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<systemitem class="library">libavcodec</systemitem> will use the lowest
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the codec will use the lowest
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possible quantizer for each macroblock (as specified by
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<option>vqmin</option>, which is 2 by default). As soon as you specify a
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low enough bitrate that <systemitem class="library">libavcodec</systemitem>
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<option>vqmin</option> for
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<systemitem class="library">libavcodec</systemitem>, which is 2 by default).
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As soon as you specify a
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low enough bitrate that the codec
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is forced to use a higher quantizer, then you are almost certainly ruining
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the quality of your video.
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In order to avoid that, you should probably downscale your video, according
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@ -333,12 +337,13 @@
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</para>
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<para>
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With constant quantizer, <systemitem
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class="library">libavcodec</systemitem> uses the same quantizer, as
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specified by the <option>vqscale</option> option, on every macroblock. If
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you want the highest quality rip possible, again ignoring bitrate, you can
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use <option>vqscale=2</option>. This will yield the same bitrate and PSNR
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(peak signal-to-noise ratio) as CBR with
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With constant quantizer, the codec uses the same quantizer, as
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specified by the <option>vqscale</option> option (for
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<systemitem class="library">libavcodec</systemitem>), on every macroblock.
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If you want the highest quality rip possible, again ignoring bitrate,
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you can use <option>vqscale=2</option>.
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This will yield the same bitrate and PSNR (peak signal-to-noise ratio)
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as CBR with
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<option>vbitrate</option>=infinity and the default <option>vqmin</option>
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of 2.
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</para>
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@ -960,7 +965,7 @@
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If you will not be encoding in constant quantizer mode, you need to
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select a bitrate.
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The concept of bitrate is quite simple.
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It's the (average) number of bits that will be consumed to store your
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It is the (average) number of bits that will be consumed to store your
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movie, per second.
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Normally bitrate is measured in kilobits (1000 bits) per second.
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The size of your movie on disk is the bitrate times the length of the
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@ -980,10 +985,10 @@
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<orderedlist>
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<listitem><para>
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<emphasis role="bold">Perceptual</emphasis>: You notice MPEG
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artifacts more if they're scaled up bigger!
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artifacts more if they are scaled up bigger!
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Artifacts appear on the scale of blocks (8x8).
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Your eye will not see errors in 4800 small blocks as easily as it
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sees errors in 1200 large blocks (assuming you'll be scaling both
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sees errors in 1200 large blocks (assuming you will be scaling both
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to fullscreen).
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</para></listitem>
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<listitem><para>
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@ -1009,7 +1014,7 @@
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However this has not been verified with theoretical or empirical
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rigor.
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Further, given that movies vary greatly with regard to noise, detail,
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degree of motion, etc., it's futile to make general recommendations
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degree of motion, etc., it is futile to make general recommendations
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for bits per length-of-diagonal (the analog of bits per pixel,
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using the square root).
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</para>
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