[MPlayer-DOCS] CVS: main/DOCS/xml/en mencoder.xml,1.62,1.63
Guillaume Poirier CVS
syncmail at mplayerhq.hu
Sat May 14 01:03:22 CEST 2005
CVS change done by Guillaume Poirier CVS
Update of /cvsroot/mplayer/main/DOCS/xml/en
In directory mail:/var2/tmp/cvs-serv8809/en
Modified Files:
mencoder.xml
Log Message:
Preparing to encode: Identifying source material and framerate + how to encode interlaced content
Index: mencoder.xml
===================================================================
RCS file: /cvsroot/mplayer/main/DOCS/xml/en/mencoder.xml,v
retrieving revision 1.62
retrieving revision 1.63
diff -u -r1.62 -r1.63
--- mencoder.xml 13 May 2005 05:30:12 -0000 1.62
+++ mencoder.xml 13 May 2005 23:03:20 -0000 1.63
@@ -519,10 +519,243 @@
for you.
</para>
+<sect2 id="menc-feat-dvd-mpeg4-preparing-encode">
+<title>Preparing to encode: Identifying source material and framerate</title>
+<para>
+ Before you even think about encoding a movie, you need to take
+ several preliminary steps.
+</para>
+
+<para>
+ The first and most important step before you encode should be
+ determining what type of content you are dealing with.
+ If your source material comes from DVD or broadcast/cable/satellite
+ TV, it will be stored in one of two formats: NTSC for North
+ America and Japan, and PAL for Europe, etc.
+ But it is important to realize that this is just the formatting for
+ presentation on a television, and often does
+ <emphasis role="bold">not</emphasis> correspond to the
+ original format of the movie.
+ In order to produce a suitable encode, you need to know the original
+ format.
+ Failure to take this into account will result in ugly combing
+ (interlacing) artifacts in your encode.
+ Besides being ugly, the artifacts also harm coding efficiency:
+ You will get worse quality per bitrate.
+</para>
+
+<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-fps">
+<title>Identifying source framerate</title>
+<para>
+ Here is a list of common types of source material, where you are
+ likely to find them, and their properties:
+</para>
+<itemizedlist>
+<listitem><para>
+ <emphasis role="bold">Standard Film</emphasis>: Produced for
+ theatrical display at 24fps.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">PAL video</emphasis>: Recorded with a PAL
+ video camera at 50 fields per second.
+ A field consists of just the even or odd numbered lines of a
+ frame.
+ Television was designed to refresh these in alternation as a
+ cheap form of analog compression.
+ The human eye supposedly compensates for this, but once you
+ understand interlacing you will learn to see it on TV too and
+ never enjoy TV again.
+ Two fields do <emphasis role="bold">not</emphasis> make a
+ complete frame, because they are captured 1/50 of a second apart
+ in time, and thus they do not line up unless there is no motion.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">NTSC Video</emphasis>: Recorded with an
+ NTSC video camera at 59.94 fields per second, or 60 fields per
+ second in the pre-color era.
+ Otherwise similar to PAL.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">Animation</emphasis>: Usually drawn at
+ 24fps, but animation also comes in mixed-framerate varieties.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">Computer Graphics (CG)</emphasis>: Can be
+ any framerate, but 24 and 30 fps are the most frequently
+ encountered in NTSC regions, and 25 fps in PAL regions.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">Old Film</emphasis>: Various lower
+ framerates.
+</para></listitem>
+</itemizedlist>
+</sect3>
+
+<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-material">
+<title>Identifying source material</title>
+<para>
+ Movies consisting of frames are referred to as progressive,
+ while those consisting of independent fields are called
+ interlaced, or sometimes video, although this latter term is
+ ambiguous.
+</para>
+<para>
+ To further complicate matters, some movies will be a mix of
+ several of the above.
+</para>
+<para>
+ The most important distinction to make between all of these
+ formats is that some are frame-based, while others are
+ field-based.
+ <emphasis role="bold">Whenever</emphasis> a movie is prepared
+ for display on television (including DVD), it is converted to a
+ field-based format.
+ The various methods by which this can be done are collectively
+ referred to as "pulldown", of which the infamous NTSC
+ "3:2 telecine" is one variety.
+ Unless the original material was also field-based (and the same
+ fieldrate), you are getting the movie in a format other than the
+ original.
+</para>
+
+<itemizedlist>
+<title>There are several common types of pulldown:</title>
+<listitem><para>
+ <emphasis role="bold">PAL 2:2 pulldown</emphasis>: The nicest of
+ them all.
+ Each frame is shown for two fields duration, by extracting the
+ even and odd lines and showing them in alternation.
+ If the original material is 24fps, this process speeds up the
+ movie by 4%.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">PAL 2:2:2:2:2:2:2:2:2:2:2:3 pulldown</emphasis>:
+ Every 12th frame is shown for three fields duration, instead of
+ just two.
+ This avoids the 4% speedup issue, but makes the process much
+ more difficult to reverse.
+ It is usually seen in musical productions where adjusting the
+ speed by 4% would seriously damage the musical score.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">NTSC 3:2 telecine</emphasis>: Frames are
+ shown alternatively for 3 fields or 2 fields duration.
+ This gives a fieldrate 5/2 times the original framerate.
+ The result is also slowed down very slightly from 60 fields per
+ second to 59.94 fields per second to maintain NTSC fieldrate.
+</para></listitem>
+<listitem><para>
+ <emphasis role="bold">NTSC 2:2 pulldown</emphasis>: Used for
+ showing 30fps material on NTSC.
+ Nice, just like 2:2 PAL pulldown.
+</para></listitem>
+</itemizedlist>
+
+<para>
+ There are also methods for converting between NTSC and PAL video.
+ Such topics are beyond the scope of this guide.
+ If you encounter such a movie and want to encode it, your best
+ bet is to find a copy in the original format.
+ NTSC/PAL conversion is highly destructive and cannot be reversed
+ cleanly, so your encode will greatly suffer if it is made from a
+ converted source.
+</para>
+<para>
+ When video is stored on DVD, consecutive pairs of fields are
+ grouped as a frame, even though they are not intended to be shown
+ at the same moment in time.
+ The MPEG-2 standard used on DVD and digital TV provides a way to
+ encode the original progressive frames, and store the number of
+ fields for which each should be shown in the frame headers.
+ If this method has been used, the term "soft telecine" will often
+ be used to describe the movie, since the process only directs the
+ DVD player to apply pulldown to the movie rather than altering
+ the movie itself.
+ This case is highly preferable since it can easily be reversed
+ (actually ignored) by the encoder, and since it preserves maximal
+ quality.
+ However, many DVD and broadcast production studios do not use
+ proper encoding techniques, and instead produce movies with
+ "hard telecine", where fields are actually duplicated in the
+ encoded MPEG-2.
+</para>
+<para>
+ The procedures for dealing with these cases will be covered later
+ in this guide.
+ For now, we leave you with some guides to identifying which type
+ of material you are dealing with:
+</para>
+
+<itemizedlist>
+<title>NTSC regions:</title>
+<listitem><para>
+ If <application>MPlayer</application> prints that the framerate
+ has changed to 23.976 when watching your movie, and never changes
+ back, it is almost certainly 24fps content that has been
+ "soft telecined".
+</para></listitem>
+<listitem><para>
+ If <application>MPlayer</application> shows the framerate
+ switching back and forth between 23.976 and 29.97, and you see
+ "combing" at times, then there are several possibilities.
+ The 23.976 fps segments are almost certainly 24fps progressive
+ content, "soft telecined", but the 29.97 fps parts could be
+ either hard-telecined 24fps content or NTSC video content.
+ Use the same guidelines as the following two cases to determine
+ which.
+</para></listitem>
+<listitem><para>
+ If <application>MPlayer</application> never shows the framerate
+ change, and every single frame with motion appears combed, your
+ movie is NTSC video at 59.94 fields per second.
+</para></listitem>
+<listitem><para>
+ If <application>MPlayer</application> never shows the framerate
+ change, and two frames out of every five appear combed, your
+ movie is "hard telecined"
+ 24fps content.
+</para></listitem>
+</itemizedlist>
+
+<itemizedlist>
+<title>PAL regions:</title>
+<listitem><para>
+ If you never see any combing, your movie is 2:2 pulldown.
+</para></listitem>
+<listitem><para>
+ If you see combing alternating in and out every half second,
+ then your movie is 2:2:2:2:2:2:2:2:2:2:2:3 pulldown.
+</para></listitem>
+<listitem><para>
+ If you always see combing during motion, then your movie is PAL
+ video at 50 fields per second.
+</para></listitem>
+</itemizedlist>
+
+<note><title>Hint:</title>
+<para>
+ <application>MPlayer</application> can slow down movie playback
+ with the -speed option.
+ Try using <option>-speed</option> 0.2 to watch the movie very
+ slowly and identify the pattern, if you cannot see it at full speed.
+</para>
+</note>
+</sect3>
+</sect2>
+
<sect2 id="menc-feat-dvd-mpeg4-2pass">
<title>Constant Quantizer vs. two pass</title>
<para>
+ It is possible to encode your movie at a wide range of qualities.
+ With modern video encoders and a bit of pre-codec compression
+ (downscaling and denoising), it is possible to achieve very good
+ quality at 700 MB, for a 90-110 minute widescreen movie.
+ And all but the longest movies can be encoded with near-perfect
+ quality at 1400 MB.
+</para>
+
+<para>
There are three approaches to encoding the video: constant bitrate
(CBR), constant quantizer, and two pass (ABR, or average bitrate).
</para>
@@ -1354,6 +1587,59 @@
</sect2>
+<sect2 id="menc-feat-dvd-mpeg4-encoding-interlaced">
+<title>Encoding interlaced video</title>
+
+<para>
+ If the movie you want to encode is interlaced (NTSC video or
+ PAL video), you will need to choose whether you want to
+ deinterlace or not.
+ While deinterlacing will make your movie usable on progressive
+ scan displays such a computer monitors and projectors, it comes
+ at a cost: The field rate of 50 or 59.94 fields per second
+ is halved to 25 or 29.97 frames per second, and roughly half
+ the information in your movie will be lost during scenes with
+ significant motion.
+</para>
+
+<para>
+ Therefore, if you are encoding for high quality archival purposes,
+ it is recommended not to deinterlace.
+ You can always deinterlace the movie at playback time when
+ displaying it on progressive scan devices, and future players will
+ be able to deinterlace to full fieldrate, interpolating 50 or
+ 59.94 entire frames per second from the interlaced video.
+</para>
+
+<para>
+Special care must be taken when working with interlaced video:
+</para>
+
+<orderedlist>
+<listitem><para>
+ Crop height and y-offset must be multiples of 4.
+</para></listitem>
+<listitem><para>
+ Any vertical scaling must be performed in interlaced mode.
+</para></listitem>
+<listitem><para>
+ Postprocessing and denoising filters may not work as expected
+ unless you take special care to operate them a field at a time,
+ and they may damage the video if used incorrectly.
+</para></listitem>
+</orderedlist>
+
+<para>
+With these things in mind, here is our first example:
+</para>
+<screen>
+ mencoder <replaceable>capture.avi</replaceable> -mc 0 -oac lavc -ovc lavc -lavcopts \
+ vcodec=mpeg2video:vbitrate=6000:ilmv:ildct:acodec=mp2:abitrate=224
+</screen>
+<para>
+Note the <option>ilmv</option> and <option>ildct</option> options.
+</para>
+</sect2>
<sect2 id="menc-feat-dvd-mpeg4-filtering">
<title>Filtering</title>
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