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<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>10.1.聽TV input</title><link rel="stylesheet" href="default.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.73.2"><link rel="start" href="index.html" title="MPlayer - The Movie Player"><link rel="up" href="tv.html" title="Chapter聽10.聽TV"><link rel="prev" href="tv.html" title="Chapter聽10.聽TV"><link rel="next" href="tv-teletext.html" title="10.2.聽Teletext"><link rel="preface" href="howtoread.html" title="How to read this documentation"><link rel="chapter" href="intro.html" title="Chapter聽1.聽Introduction"><link rel="chapter" href="install.html" title="Chapter聽2.聽Installation"><link rel="chapter" href="usage.html" title="Chapter聽3.聽Usage"><link rel="chapter" href="cd-dvd.html" title="Chapter聽4.聽CD/DVD usage"><link rel="chapter" href="faq.html" title="Chapter聽5.聽Frequently Asked Questions"><link rel="chapter" href="containers.html" title="Chapter聽6.聽Containers"><link rel="chapter" href="codecs.html" title="Chapter聽7.聽Codecs"><link rel="chapter" href="video.html" title="Chapter聽8.聽Video output devices"><link rel="chapter" href="audio.html" title="Chapter聽9.聽Audio output devices"><link rel="chapter" href="tv.html" title="Chapter聽10.聽TV"><link rel="chapter" href="radio.html" title="Chapter聽11.聽Radio"><link rel="chapter" href="ports.html" title="Chapter聽12.聽Ports"><link rel="chapter" href="mencoder.html" title="Chapter聽13.聽Basic usage of MEncoder"><link rel="chapter" href="encoding-guide.html" title="Chapter聽14.聽Encoding with MEncoder"><link rel="appendix" href="bugreports.html" title="Appendix聽A.聽How to report bugs"><link rel="appendix" href="bugs.html" title="Appendix聽B.聽Known bugs"><link rel="appendix" href="skin.html" title="Appendix聽C.聽MPlayer skin format"><link rel="appendix" href="history.html" title="Appendix聽D.聽History"><link rel="subsection" href="tv-input.html#tv-compilation" title="10.1.1.聽Compilation"><link rel="subsection" href="tv-input.html#tv-tips" title="10.1.2.聽Usage tips"><link rel="subsection" href="tv-input.html#tv-examples" title="10.1.3.聽Examples"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">10.1.聽TV input</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="tv.html">Prev</a>聽</td><th width="60%" align="center">Chapter聽10.聽TV</th><td width="20%" align="right">聽<a accesskey="n" href="tv-teletext.html">Next</a></td></tr></table><hr></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="tv-input"></a>10.1.聽TV input</h2></div></div></div><p>
This section is about how to enable <span class="bold"><strong>watching/grabbing
from V4L compatible TV tuner</strong></span>. See the man page for a description
of TV options and keyboard controls.
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="tv-compilation"></a>10.1.1.聽Compilation</h3></div></div></div><div class="procedure"><ol type="1"><li><p>
First, you have to recompile. <tt class="filename">./configure</tt> will
autodetect kernel headers of v4l stuff and the existence of
<tt class="filename">/dev/video*</tt> entries. If they exist, TV support will
be built (see the output of <tt class="filename">./configure</tt>).
</p></li><li><p>
Make sure your tuner works with another TV software in Linux, for
example <span class="application">XawTV</span>.
</p></li></ol></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="tv-tips"></a>10.1.2.聽Usage tips</h3></div></div></div><p>
The full listing of the options is available on the manual page.
Here are just a few tips:
</p><div class="itemizedlist"><ul type="disc"><li><p>
Use the <tt class="option">channels</tt> option. An example:
</p><pre class="screen">-tv channels=26-MTV1,23-TV2</pre><p>
Explanation: Using this option, only the 26 and 23 channels will be usable,
and there will be a nice OSD text upon channel switching, displaying the
channel's name. Spaces in the channel name must be replaced by the
"_" character.
</p></li><li><p>
Choose some sane image dimensions. The dimensions of the resulting image
should be divisible by 16.
</p></li><li><p>
If you capture the video with the vertical resolution higher than half
of the full resolution (i.e. 288 for PAL or 240 for NTSC), then the
'frames' you get will really be interleaved pairs of fields.
Depending on what you want to do with the video you may leave it in
this form, destructively deinterlace, or break the pairs apart into
individual fields.
</p><p>
Otherwise you'll get a movie which is distorted during
fast-motion scenes and the bitrate controller will be probably even unable
to retain the specified bitrate as the interlacing artifacts produce high
amount of detail and thus consume lot of bandwidth. You can enable
deinterlacing with <tt class="option">-vf pp=DEINT_TYPE</tt>.
Usually <tt class="option">pp=lb</tt> does a good job, but it can be matter of
personal preference.
See other deinterlacing algorithms in the manual and give it a try.
</p></li><li><p>
Crop out the dead space. When you capture the video, the areas at the edges
are usually black or contain some noise. These again consume lots of
unnecessary bandwidth. More precisely it's not the black areas themselves
but the sharp transitions between the black and the brighter video image
which do but that's not important for now. Before you start capturing,
adjust the arguments of the <tt class="option">crop</tt> option so that all the
crap at the margins is cropped out. Again, don't forget to keep the resulting
dimensions sane.
</p></li><li><p>
Watch out for CPU load. It shouldn't cross the 90% boundary for most of the
time. If you have a large capture buffer, <span class="application">MEncoder</span>
can survive an overload for few seconds but nothing more. It's better to
turn off the 3D OpenGL screensavers and similar stuff.
</p></li><li><p>
Don't mess with the system clock. <span class="application">MEncoder</span> uses the
system clock for doing A/V sync. If you adjust the system clock (especially
backwards in time), <span class="application">MEncoder</span> gets confused and you
will lose frames. This is an important issue if you are hooked to a network
and run some time synchronization software like NTP. You have to turn NTP
off during the capture process if you want to capture reliably.
</p></li><li><p>
Don't change the <tt class="option">outfmt</tt> unless you know what you are doing
or your card/driver really doesn't support the default (YV12 colorspace).
In the older versions of <span class="application">MPlayer</span>/
<span class="application">MEncoder</span> it was necessary to specify the output
format. This issue should be fixed in the current releases and
<tt class="option">outfmt</tt> isn't required anymore, and the default suits the
most purposes. For example, if you are capturing into DivX using
<code class="systemitem">libavcodec</code> and specify
<tt class="option">outfmt=RGB24</tt> in order to increase the quality of the captured
images, the captured image will be actually later converted back into YV12 so
the only thing you achieve is a massive waste of CPU power.
</p></li><li><p>
To specify the I420 colorspace (<tt class="option">outfmt=i420</tt>), you have to
add an option <tt class="option">-vc rawi420</tt> due to a fourcc conflict with an
Intel Indeo video codec.
</p></li><li><p>
There are several ways of capturing audio. You can grab the sound either using
your sound card via an external cable connection between video card and
line-in, or using the built-in ADC in the bt878 chip. In the latter case, you
have to load the <span class="bold"><strong>btaudio</strong></span> driver. Read the
<tt class="filename">linux/Documentation/sound/btaudio</tt> file (in the kernel
tree, not <span class="application">MPlayer</span>'s) for some instructions on using
this driver.
</p></li><li><p>
If <span class="application">MEncoder</span> cannot open the audio device, make
sure that it is really available. There can be some trouble with the sound
servers like aRts (KDE) or ESD (GNOME). If you have a full duplex sound card
(almost any decent card supports it today), and you are using KDE, try to
check the "full duplex" option in the sound server preference menu.
</p></li></ul></div><p>
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="tv-examples"></a>10.1.3.聽Examples</h3></div></div></div><div class="informalexample"><p>
Dummy output, to AAlib :)
</p><pre class="screen">mplayer -tv driver=dummy:width=640:height=480 -vo aa tv://</pre><p>
</p></div><div class="informalexample"><p>
Input from standard V4L:
</p><pre class="screen">
mplayer -tv driver=v4l:width=640:height=480:outfmt=i420 -vc rawi420 -vo xv tv://
</pre><p>
</p></div><div class="informalexample"><p>
A more sophisticated example. This makes <span class="application">MEncoder</span>
capture the full PAL image, crop the margins, and deinterlace the picture
using a linear blend algorithm. Audio is compressed with a constant bitrate
of 64kbps, using LAME codec. This setup is suitable for capturing movies.
</p><pre class="screen">
mencoder -tv driver=v4l:width=768:height=576 -oac mp3lame -lameopts cbr:br=64\
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=900 \
-vf crop=720:544:24:16,pp=lb -o <em class="replaceable"><code>output.avi</code></em> tv://
</pre><p>
</p></div><div class="informalexample"><p>
This will additionally rescale the image to 384x288 and compresses the
video with the bitrate of 350kbps in high quality mode. The vqmax option
looses the quantizer and allows the video compressor to actually reach so
low bitrate even at the expense of the quality. This can be used for
capturing long TV series, where the video quality isn't so important.
</p><pre class="screen">
mencoder -tv driver=v4l:width=768:height=576 \
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=350:vhq:vqmax=31:keyint=300 \
-oac mp3lame -lameopts cbr:br=48 -sws 1 -o <em class="replaceable"><code>output.avi</code></em>\
-vf crop=720:540:24:18,pp=lb,scale=384:288 tv://
</pre><p>
It's also possible to specify smaller image dimensions in the
<tt class="option">-tv</tt> option and omit the software scaling but this approach
uses the maximum available information and is a little more resistant to noise.
The bt8x8 chips can do the pixel averaging only in the horizontal direction due
to a hardware limitation.
</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="tv.html">Prev</a>聽</td><td width="20%" align="center"><a accesskey="u" href="tv.html">Up</a></td><td width="40%" align="right">聽<a accesskey="n" href="tv-teletext.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter聽10.聽TV聽</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">聽10.2.聽Teletext</td></tr></table></div></body></html>
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