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Telecine HOWTO by Corey Hickey <bugfood-ml@fatooh.org>, some modifications

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by my humble self.


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@ -761,4 +761,548 @@ mencoder dvd://1 -aid 128 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vqscale=3:v
</sect1>
<sect1 id="menc-feat-telecine">
<title>How to deal with telecine and interlacing within NTSC DVDs</title>
<formalpara>
<title>Introduction</title>
<para>
I suggest you visit this page if you don't understand much of what
is written in this document:
<ulink url="http://www.divx.com/support/guides/guide.php?gid=10">http://www.divx.com/support/guides/guide.php?gid=10</ulink>
This URL links to an understandable and reasonably comprehensive
description of what telecine is.
</para></formalpara>
<para>
For technical reasons pertaining to the limitations of early
television hardware, all video intended to be displayed on an NTSC
television set must be 59.94 fields per second. Made-for-TV movies
and shows are often filmed directly at 59.94 fields per second, but
the majority of cinema is filmed at 24 or 23.976 frames per
second. When cinematic movie DVDs are mastered, the video is then
converted for television using a process called telecine.
</para>
<para>
On a DVD, the video is never actually stored as 59.94 fields per
second. For video that was originally 59.94, each pair of fields is
combined to form a frame, resulting in 29.97 frames per
second. Hardware DVD players then read a flag embedded in the video
stream to determine whether the odd- or even-numbered lines should
form the first field.
</para>
<para>
Usually, 23.976 frames per second content stays as it is when
encoded for a DVD, and the DVD player must perform telecining
on-the-fly. Sometimes, however, the video is telecined
<emphasis>before</emphasis> being stored on the DVD; even though it
was originally 23.976 frames per second, it becomes 59.94 fields per
second, and is stored on the disk as 29.97 frames per second.
</para>
<para>
When looking at individual frames formed from 59.94 fields per
second video, telecined or otherwise, interlacing is clearly visible
wherever there is any motion, because one field (say, the
even-numbered lines) represents a moment in time 1/59.94th of a
second later than the other. Playing interlaced video on a computer
looks ugly both because the monitor is higher resolution and because
the video is shown frame-after-frame instead of field-after-field.
</para>
<para>
Notes:
</para>
<itemizedlist>
<listitem><para>
This section only applies to NTSC DVDs, and not PAL.
</para></listitem>
<listitem><para>
The example <application>MEncoder</application> lines throughout the
document are <emphasis role="bold">not</emphasis> intended for
actual use. They are simply the bare minimum required to encode the
pertaining video category. How to make good DVD rips or fine-tune
<systemitem class="library">libavcodec</systemitem> for maximum
quality is not within the scope of this document.
</para></listitem>
<listitem><para>
There are a couple footnotes specific to this guide, linked like this:
<link linkend="menc-feat-telecine-footnotes">[1]</link>
</para></listitem>
</itemizedlist>
<sect2 id="menc-feat-telecine-ident">
<title>How to tell what type of video you have</title>
<sect3 id="menc-feat-telecine-ident-progressive">
<title>Progressive</title>
<para>
Progressive video was originally filmed at 23.976 fps, and stored
on the DVD without alteration.
</para>
<para>
When you play a progressive DVD in <application>MPlayer</application>,
<application>MPlayer</application> will print the following line as
soon as the movie begins to play:
<screen> demux_mpg: 24fps progressive NTSC content detected, switching framerate.</screen>
From this point forward, demux_mpg should never say it finds
&quot;30fps NTSC content.&quot;
</para>
<para>
When you watch progressive video, you should never see any
interlacing. Beware, however, because sometimes there is a tiny bit
of telecine mixed in, where you wouldn't expect. I've encountered TV
show DVDs that have one second of telecine at every scene change, or
at seemingly random places. I once watched a DVD that had a
progressive first half, and the second half was telecined. If you
want to be <emphasis>really</emphasis> thorough, you can scan the
entire movie:
<screen>mplayer dvd://1 -nosound -vo null -benchmark</screen>
Using <option>-benchmark</option> makes
<application>MPlayer</application> play the movie as quickly as it
possibly can; still, depending on your hardware, it can take a
while. Every time demux_mpg reports a framerate change, the line
immediately above will show you the time at which the change
occurred.
</para>
<para>
Sometimes progressive video is referred to as &quot;soft-telecine&quot;
because it is intended to be telecined by the DVD player.
</para>
</sect3>
<sect3 id="menc-feat-telecine-ident-telecined">
<title>Telecined</title>
<para>
Telecined video was originally filmed at 23.976, but was telecined
<emphasis>before</emphasis> it was written to the DVD.
</para>
<para>
<application>MPlayer</application> does not (ever) report any
framerate changes when it plays telecined video.
</para>
<para>
Watching a telecined video, you will see interlacing artifacts that
seem to &quot;blink&quot;: they repeatedly appear and disappear.
You can look closely at this by
<orderedlist>
<listitem>
<screen>mplayer dvd://1 -speed 0.1</screen>
</listitem>
<listitem><para>
Seek to a part with motion.
</para></listitem>
<listitem><para>
Look at the pattern of interlaced-looking and progressive-looking
frames. If the pattern you see is PPPII,PPPII,PPPII,... then the
video is telecined. If you see some other pattern, then the video
may have been telecined using some non-standard method and
<application>MEncoder</application> cannot losslessly convert it
to progressive. If you don't see any pattern at all, then it is
most likely interlaced.
</para></listitem>
</orderedlist>
</para>
<para>
Sometimes telecined video is referred to as &quot;hard-telecine&quot;.
</para>
</sect3>
<sect3 id="menc-feat-telecine-ident-interlaced">
<title>Interlaced</title>
<para>
Interlaced video was originally filmed at 59.94 fields per second,
and stored on the DVD as 29.97 frames per second. The interlacing is
a result of combining pairs of fields into frames, because within
each frame, each field is 1/59.94 seconds apart.
</para>
<para>
As with telecined video, <application>MPlayer</application> should
not ever report any framerate changes when playing interlaced content.
</para>
<para>
When you view an interlaced video closely with <option>-speed 0.1</option>,
you will see that every single frame is interlaced.
</para>
</sect3>
<sect3 id="menc-feat-telecine-ident-mixedpt">
<title>Mixed progressive and telecine</title>
<para>
All of a &quot;mixed progressive and telecine&quot; video was originally
23.976 frames per second, but some parts of it ended up being telecined.
</para>
<para>
When <application>MPlayer</application> plays this category, it will
(often repeatedly) switch back and forth between &quot;30fps
NTSC&quot; and &quot;24fps progressive NTSC&quot;. Watch the bottom of
<application>MPlayer's</application> output to see these messages.
</para>
<para>
You should check the &quot;30fps NTSC&quot; sections to make sure
they are actually telecine, and not just interlaced.
</para>
</sect3>
<sect3 id="menc-feat-telecine-ident-mixedpi">
<title>Mixed progressive and interlaced</title>
<para>
In &quot;mixed progressive and interlaced&quot; content, progressive
and interlaced video have been have been spliced together.
</para>
<para>
This category looks just like &quot;mixed progressive and telecine&quot;,
until you examine the 30fps sections and see that they don't have the
telecine pattern.
</para>
</sect3>
</sect2>
<sect2 id="menc-feat-telecine-encode">
<title>How to encode each category</title>
<para>
As I mentioned in the beginning, example <application>MEncoder</application>
lines below are <emphasis role="bold">not</emphasis> meant to actually be used;
they only demonstrate the minimum parameters to properly encode each category.
</para>
<sect3 id="menc-feat-telecine-encode-progressive">
<title>Progressive</title>
<para>
Progressive video requires no special filtering to encode. The only
parameter you need to be sure to use is
<option>-ofps 23.976</option>. Otherwise, <application>MEncoder</application>
will try to encode at 29.97 fps and duplicate frames.
</para>
<para>
<screen>mencoder dvd://1 -nosound -ovc lavc -ofps 23.976</screen>
</para>
</sect3>
<sect3 id="menc-feat-telecine-encode-telecined">
<title>Telecined</title>
<para>
Telecine can be reversed to retrieve the original 23.976 content,
using a process called inverse-telecine.
<application>MPlayer</application> contains two filters to
accomplish this: <option>detc</option> and
<option>ivtc</option>. You can read the manual page to see their
differences, but for DVDs I've never had a problem with
<option>ivtc</option>. Note that you should
<emphasis role="bold">always</emphasis> inverse-telecine before any
rescaling; unless you really know what you're doing,
inverse-telecine before cropping, too
<link linkend="menc-feat-telecine-footnotes">[1]</link>. Again,
<option>-ofps 23.976</option> is needed, too.
</para>
<para>
<screen>mencoder dvd://1 -nosound -vf ivtc=1 -ovc lavc -ofps 23.976</screen>
</para>
</sect3>
<sect3 id="menc-feat-telecine-encode-interlaced">
<title>Interlaced</title>
<para>
For most practical cases it is not possible to retrieve a complete
progressive video from interlaced content. The only way to do so
without losing half of the vertical resolution is to double the
framerate and try to &quot;guess&quot; what ought to make up the
corresponding lines for each field (this has drawbacks - see method
3).
</para>
<orderedlist>
<listitem><para>
Encode the video in interlaced form. Normally, interlacing wreaks
havoc with the encoder's ability to compress well, but
<systemitem class="library">libavcodec</systemitem> has two
parameters specifically for dealing with storing interlaced video a
bit better: <option> ildct</option> and <option>ilme</option>. Also,
using <option>mbd=2</option> is strongly recommended
<link linkend="menc-feat-telecine-footnotes">[2] </link> because it
will encode macroblocks as non-interlaced in places where there is
no motion. Note that <option>-ofps</option> is NOT needed here.
<screen>mencoder dvd://1 -nosound -ovc lavc -lavcopts ildct:ilme:mbd=2</screen>
</para></listitem>
<listitem><para>
Use a deinterlacing filter before encoding. There are several of
these filters available to choose from, each with its own advantages
and disadvantages. Consult <option>mplayer -pphelp</option> to see
what's available (grep for &quot;deint&quot;), and search the
<ulink url="http://www.mplayerhq.hu/homepage/design6/info.html#mailing_lists">
MPlayer mailing lists</ulink> to find many discussions about the
various filters. Again, the framerate is not changing, so no
<option>-ofps</option>. Also, deinterlacing should be done after
cropping <link linkend="menc-feat-telecine-footnotes">[1]</link> and
before scaling.
<screen>mencoder dvd://1 -nosound -vf pp=lb -ovc lavc</screen>
</para></listitem>
<listitem><para>
Unfortunately, this option is buggy with
<application>MEncoder</application>; it ought to work well with
<application>MEncoder G2</application>, but that isn't here yet. You
might experience crahes. Anyway, the purpose of <option> -vf
tfields</option> is to create a full frame out of each field, which
makes the framerate 59.94. The advantage of this approach is that no
data is ever lost; however, since each frame comes from only one
field, the missing lines have to be interpolated somehow. There are
no very good methods of generating the missing data, and so the
result will look a bit similar to when using some deinterlacing
filters. Generating the missing lines creates other issues, as well,
simply because the amount of data doubles. So, higher encoding
bitrates are required to maintain quality, and more CPU power is
used for both encoding and decoding. tfields has several different
options for how to create the missing lines of each frame. If you
use this method, then Reference the manual, and chose whichever
option looks best for your material. Note that when using
<option>tfields</option> you
<emphasis role="bold">have to </emphasis> specify both
<option>-fps</option> and <option>-ofps</option> to be twice the
framerate of your original source.
<screen>mencoder dvd://1 -nosound -vf tfields=2 -ovc lavc -fps 59.94 -ofps 59.94</screen>
</para></listitem>
<listitem><para>
If you plan on downscaling dramatically, you can excise and encode
only one of the two fields. Of course, you'll lose half the vertical
resolution, but if you plan on downscaling to at most 1/2 of the
original, the loss won't matter much. The result will be a
progressive 29.97 frames per second file. The procedure is to use
<option>-vf field</option>, then crop
<link linkend="menc-feat-telecine-footnotes">[1]</link> and scale
appropriately. Remember that you'll have to adjust the scale to
compensate for the vertical resolution being halved.
<screen>mencoder dvd://1 -nosound -vf field=0 -ovc lavc</screen>
</para></listitem>
</orderedlist>
</sect3>
<sect3 id="menc-feat-telecine-encode-mixedpt">
<title>Mixed progressive and telecine</title>
<para>
In order to turn mixed progressive and telecine video into entirely
progressive video, the telecined parts have to be
inverse-telecined. There are two filters that accomplish this
natively, but a better solution most of the time is to use two
filters in conjunction (read onward for more detail).
</para>
<itemizedlist>
<listitem><para>
Currently the most reliable method to deal with this type of video
is to, rather than inverse-telecine the telecined parts, telecine
the non-telecined parts and then inverse-telecine the whole
video. Sound confusing? softpulldown is a filter that goes through
a video and makes the entire file telecined. If we follow
softpulldown with either <option>detc</option> or
<option>ivtc</option>, the final result will be entirely
progressive. Cropping and scaling should be done after the
inverse-telecine operations, and <option> -ofps 23.976</option> is
needed.
<screen>mencoder dvd://1 -nosound -vf softpulldown,ivtc=1 -ovc lavc -ofps 23.976</screen>
</para>
</listitem>
<listitem><para>
<option>-vf pullup</option> is designed to inverse-telecine
telecined material while leaving progressive data alone. Pullup
doesn't really work well with the current
<application>MEncoder</application>, though, and is really intended
for use with <application>MEncoder G2</application> (whenever it's
ready). It works fine without <option>-ofps</option>, but
<option>-ofps</option> is needed to prevent choppy output. With
<option>-ofps</option>, it sometimes fails. The problems arise from
<application>MEncoder's</application> behavior of dropping frames to
maintain synchronization between the audio and video: it drops
frames before sending them through the filter chain, rather than
after. As a result, <option>pullup</option> is sometimes deprived
of the data it needs.
</para>
<para>
If <application>MEncoder</application> drops too many frames in a
row, it starves <option>pullup</option>'s buffers and causes it to
crash.
</para>
<para>
Even if <application>MEncoder</application> only drops one frame,
<option> pullup</option> still doesn't get to see it, and will end
up operating on an incorrect sequence of frames. Even though this
doesn't cause a crash, <option> pullup</option> won't be able to
make correct decisions on how to reassemble progressive frames, and
will either match fields together incorrectly or drop several fields
to compensate.
</para>
</listitem>
<listitem><para>
I haven't used <option>-vf filmdint</option> myself, but here's what
D Richard Felker III has to say:
<blockquote><para>It's OK, but IMO it tries to deinterlace rather
than doing inverse telecine too often (much like settop DVD
players &amp; progressive TVs) which gives ugly flickering and
other artefacts. If you're going to use it, you at least need to
spend some time tuning the options and watching the output first
to make sure it's not messing up.</para></blockquote>
</para></listitem>
</itemizedlist>
</sect3>
<sect3 id="menc-feat-telecine-encode-mixedpi">
<title>Mixed progressive and interlaced</title>
<para>
There are two options for dealing with this category, each of
which is a compromise. You should decide based on the
duration/location of each type.
</para>
<itemizedlist>
<listitem><para>
Treat it as progressive. The interlaced parts will look interlaced,
and some of the interlaced fields will have to be dropped, resulting
in a bit of uneven jumpiness. You can use a postprocessing filter if
you want to, but it may slightly degrade the progressive parts.
</para>
<para>
This option should definitely not be used if you want to eventually
display the video on an interlaced device (with a TV card, for
example). If you have interlaced frames in a 23.976 frames per
second video, they will be telecined along with the progressive
frames. Half of the interlaced "frames" will be displayed for three
fields' duration (3/59.94 seconds), resulting in a flicking
&quot;jump back in time&quot; effect that looks quite bad. If you
even attempt this, you <emphasis role="bold">must</emphasis> use a
deinterlacing filter like <option>lb</option> or
<option>l5</option>.
</para>
<para>
It may also be a bad idea for progressive display, too. It will drop
pairs of consecutive interlaced fields, resulting in a discontinuity
that can be more visible than with the second method, which shows
some progressive frames twice. 29.97 frames per second interlaced
video is already a bit choppy because it really should be shown at
59.94 fields per second, so the duplicate frames don't stand out as
much.
</para>
<para>
Either way, it's best to consider your content and how you intend to
display it. If your video is 90% progressive and you never intend to
show it on a TV, you should favor a progressive approach. If it's
only half progressive, you probably want to encode it as if it's all
interlaced.
</para>
</listitem>
<listitem><para>
Treat it as interlaced. Some frames of the progressive parts will
need to be duplicated, resulting in uneven jumpiness. Again,
deinterlacing filters may slightly degrade the progressive parts.
</para></listitem>
</itemizedlist>
</sect3>
</sect2>
<sect2 id="menc-feat-telecine-footnotes">
<title>Footnotes</title>
<orderedlist>
<listitem><formalpara>
<title>About cropping:</title>
<para>
Video data on DVDs are stored in a format called YUV 4:2:0. In YUV
video, luma (&quot;brightness&quot;) and chroma (&quot;color&quot;)
are stored separately. Because the human eye is somewhat less
sensitive to color than it is to brightness, in a YUV 4:2:0 picture
there is only one chroma pixel for every four luma pixels. In a
progressive picture, each square of four luma pixels (two on each
side) has one common chroma pixel. You must crop progressive YUV
4:2:0 to even resolutions, and use even offsets. For example,
<option>crop=716:380:2:26</option> is OK but
<option>crop=716:380:3:26 </option> is not.
</para>
</formalpara>
<para>
When you are dealing with interlaced YUV 4:2:0, the situation is a
bit more complicated. Instead of every four luma pixels in the
<emphasis>frame </emphasis> sharing a chroma pixel, every four luma
pixels in each <emphasis> field</emphasis> share a chroma
pixel. When fields are interlaced to form a frame, each scanline is
one pixel high. Now, instead of all four luma pixels being in a
square, there are two pixels side-by-side, and the other two pixels
are side-by-side two scanlines down. The two luma pixels in the
intermediate scanline are from the other field, and so share a
different chroma pixel with two luma pixels two scanlines away. All
this confusion makes it necessary to have vertical crop dimensions
and offsets be multiples of four. Horizontal can stay even.
</para>
<para>
For telecined video, I recommend that cropping take place after
inverse telecining. Once the video is progressive you only need to
crop by even numbers. If you really want to gain the slight speedup
that cropping first may offer, you must crop vertically by multiples
of four or else the inverse-telecine filter won't have proper data.
</para>
<para>
For interlaced (not telecined) video, you must always crop
vertically by multiples of four unless you use <option>-vf
field</option> before cropping.
</para>
</listitem>
<listitem><formalpara>
<title>About encoding parameters and quality:</title>
<para>
Just because I recommend <option>mbd=2</option> here doesn't mean it
shouldn't be used elsewhere. Along with <option>trell</option>,
<option>mbd=2</option> is one of the two
<systemitem class="library">libavcodec</systemitem> options that
increases quality the most, and you should always use at least those
two unless the drop in encoding speed is prohibitive (e.g. realtime
encoding). There are many other options to
<systemitem class="library">libavcodec</systemitem> that increase
encoding quality (and decrease encoding speed) but that is beyond
the scope of this document.
</para>
</formalpara>
</listitem>
</orderedlist>
</sect2>
</sect1>
</chapter>