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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>14.3.Encoding with the libavcodec
codec family</title><link rel="stylesheet" href="default.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.68.1"><link rel="start" href="index.html" title="MPlayer - The Movie Player"><link rel="up" href="encoding-guide.html" title="Chapter14.Encoding with MEncoder"><link rel="prev" href="menc-feat-telecine.html" title="14.2.How to deal with telecine and interlacing within NTSC DVDs"><link rel="next" href="menc-feat-xvid.html" title="14.4.Encoding with the XviD
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codec family</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="menc-feat-telecine.html">Prev</a></td><th width="60%" align="center">Chapter14.Encoding with <span class="application">MEncoder</span></th><td width="20%" align="right"><a accesskey="n" href="menc-feat-xvid.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="menc-feat-enc-libavcodec"></a>14.3.Encoding with the <code class="systemitem">libavcodec</code>
codec family</h2></div></div></div><p>
<a href="video-codecs.html#ffmpeg" title="7.1.1.FFmpeg/libavcodec"><code class="systemitem">libavcodec</code></a>
provides simple encoding to a lot of interesting video and audio formats.
You can encode to the following codecs (more or less up to date):
</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="menc-feat-enc-libavcodec-video-codecs"></a>14.3.1.<code class="systemitem">libavcodec</code>'s video codecs</h3></div></div></div><p>
</p><div class="informaltable"><table border="1"><colgroup><col><col></colgroup><thead><tr><th>Video codec name</th><th>Description</th></tr></thead><tbody><tr><td>mjpeg</td><td>
Motion JPEG
</td></tr><tr><td>ljpeg</td><td>
lossless JPEG
</td></tr><tr><td>h261</td><td>
H.261
</td></tr><tr><td>h263</td><td>
H.263
</td></tr><tr><td>h263p</td><td>
H.263+
</td></tr><tr><td>mpeg4</td><td>
ISO standard MPEG-4 (DivX, XviD compatible)
</td></tr><tr><td>msmpeg4</td><td>
pre-standard MPEG-4 variant by MS, v3 (AKA DivX3)
</td></tr><tr><td>msmpeg4v2</td><td>
pre-standard MPEG-4 by MS, v2 (used in old ASF files)
</td></tr><tr><td>wmv1</td><td>
Windows Media Video, version 1 (AKA WMV7)
</td></tr><tr><td>wmv2</td><td>
Windows Media Video, version 2 (AKA WMV8)
</td></tr><tr><td>rv10</td><td>
RealVideo 1.0
</td></tr><tr><td>rv20</td><td>
RealVideo 2.0
</td></tr><tr><td>mpeg1video</td><td>
MPEG-1 video
</td></tr><tr><td>mpeg2video</td><td>
MPEG-2 video
</td></tr><tr><td>huffyuv</td><td>
lossless compression
</td></tr><tr><td>asv1</td><td>
ASUS Video v1
</td></tr><tr><td>asv2</td><td>
ASUS Video v2
</td></tr><tr><td>ffv1</td><td>
FFmpeg's lossless video codec
</td></tr><tr><td>svq1</td><td>
Sorenson video 1
</td></tr><tr><td>flv</td><td>
Sorenson H.263 used in Flash Video
</td></tr><tr><td>dvvideo</td><td>
Sony Digital Video
</td></tr><tr><td>snow</td><td>
FFmpeg's experimental wavelet-based codec
</td></tr></tbody></table></div><p>
The first column contains the codec names that should be passed after the
<code class="literal">vcodec</code> config, like: <tt class="option">-lavcopts vcodec=msmpeg4</tt>
</p><div class="informalexample"><p>
An example with MJPEG compression:
</p><pre class="screen">mencoder dvd://2 -o title2.avi -ovc lavc -lavcopts vcodec=mjpeg -oac copy</pre><p>
</p></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="menc-feat-enc-libavcodec-audio-codecs"></a>14.3.2.<code class="systemitem">libavcodec</code>'s audio codecs</h3></div></div></div><p>
</p><div class="informaltable"><table border="1"><colgroup><col><col></colgroup><thead><tr><th>Audio codec name</th><th>Description</th></tr></thead><tbody><tr><td>mp2</td><td>MPEG Layer 2</td></tr><tr><td>ac3</td><td>AC3, AKA Dolby Digital</td></tr><tr><td>adpcm_ima_wav</td><td>IMA adaptive PCM (4 bits per sample, 4:1 compression)</td></tr><tr><td>sonic</td><td>experimental lossy/lossless codec</td></tr></tbody></table></div><p>
The first column contains the codec names that should be passed after the
<code class="literal">acodec</code> option, like: <tt class="option">-lavcopts acodec=ac3</tt>
</p><div class="informalexample"><p>
An example with AC3 compression:
</p><pre class="screen">mencoder dvd://2 -o title2.avi -oac lavc -lavcopts acodec=ac3 -ovc copy</pre><p>
</p></div><p>
Contrary to <code class="systemitem">libavcodec</code>'s video
codecs, its audio codecs do not make a wise usage of the bits they are
given as they lack some minimal psychoacoustic model (if at all)
which most other codec implementations feature.
However, note that all these audio codecs are very fast and work
out-of-the-box everywhere <span class="application">MEncoder</span> has been
compiled with <code class="systemitem">libavcodec</code> (which
is the case most of time), and do not depend on external libraries.
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="menc-feat-dvd-mpeg4-lavc-encoding-options"></a>14.3.3.Encoding options of libavcodec</h3></div></div></div><p>
Ideally, you would probably want to be able to just tell the encoder to switch
into "high quality" mode and move on.
That would probably be nice, but unfortunately hard to implement as different
encoding options yield different quality results depending on the source material.
That is because compression depends on the visual properties of the video
in question.
For example, anime and live action have very different properties and
thus require different options to obtain optimum encoding.
The good news is that some options should never be left out, like
<tt class="option">mbd=2</tt>, <tt class="option">trell</tt>, and <tt class="option">v4mv</tt>.
See below for a detailed description of common encoding options.
</p><div class="itemizedlist"><p class="title"><b>Options to adjust:</b></p><ul type="disc"><li><p>
<span class="bold"><strong>vmax_b_frames</strong></span>: 1 or 2 is good, depending on
the movie.
Note that if you need to have your encode be decodable by DivX5, you
need to activate closed GOP support, using
<code class="systemitem">libavcodec</code>'s <tt class="option">cgop</tt>
option, but you need to deactivate scene detection, which
is not a good idea as it will hurt encode efficiency a bit.
</p></li><li><p>
<span class="bold"><strong>vb_strategy=1</strong></span>: helps in high-motion scenes.
On some videos, vmax_b_frames may hurt quality, but vmax_b_frames=2 along
with vb_strategy=1 helps.
</p></li><li><p>
<span class="bold"><strong>dia</strong></span>: motion search range. Bigger is better
and slower.
Negative values are a completely different scale.
Good values are -1 for a fast encode, or 2-4 for slower.
</p></li><li><p>
<span class="bold"><strong>predia</strong></span>: motion search pre-pass.
Not as important as dia. Good values are 1 (default) to 4. Requires preme=2
to really be useful.
</p></li><li><p>
<span class="bold"><strong>cmp, subcmp, precmp</strong></span>: Comparison function for
motion estimation.
Experiment with values of 0 (default), 2 (hadamard), 3 (dct), and 6 (rate
distortion).
0 is fastest, and sufficient for precmp.
For cmp and subcmp, 2 is good for anime, and 3 is good for live action.
6 may or may not be slightly better, but is slow.
</p></li><li><p>
<span class="bold"><strong>last_pred</strong></span>: Number of motion predictors to
take from the previous frame.
1-3 or so help at little speed cost.
Higher values are slow for no extra gain.
</p></li><li><p>
<span class="bold"><strong>cbp, mv0</strong></span>: Controls the selection of macroblocks.
Small speed cost for small quality gain.
</p></li><li><p>
<span class="bold"><strong>qprd</strong></span>: adaptive quantization based on the
macroblock's complexity.
May help or hurt depending on the video and other options.
This can cause artifacts unless you set vqmax to some reasonably small value
(6 is good, maybe as low as 4); vqmin=1 should also help.
</p></li><li><p>
<span class="bold"><strong>qns</strong></span>: very slow, especially when combined
with qprd.
This option will make the encoder minimize noise due to compression
artifacts instead of making the encoded video strictly match the source.
Do not use this unless you have already tweaked everything else as far as it
will go and the results still are not good enough.
</p></li><li><p>
<span class="bold"><strong>vqcomp</strong></span>: Tweak ratecontrol.
What values are good depends on the movie.
You can safely leave this alone if you want.
Reducing vqcomp puts more bits on low-complexity scenes, increasing it puts
them on high-complexity scenes (default: 0.5, range: 0-1. recommended range:
0.5-0.7).
</p></li><li><p>
<span class="bold"><strong>vlelim, vcelim</strong></span>: Sets the single coefficient
elimination threshold for luminance and chroma planes.
These are encoded separately in all MPEG-like algorithms.
The idea behind these options is to use some good heuristics to determine
when the change in a block is less than the threshold you specify, and in
such a case, to just encode the block as "no change".
This saves bits and perhaps speeds up encoding. vlelim=-4 and vcelim=9
seem to be good for live movies, but seem not to help with anime;
when encoding animation, you should probably leave them unchanged.
</p></li><li><p>
<span class="bold"><strong>qpel</strong></span>: Quarter pixel motion estimation.
MPEG-4 uses half pixel precision for its motion search by default,
therefore this option comes with an overhead as more information will be
stored in the encoded file.
The compression gain/loss depends on the movie, but it is usually not very
effective on anime.
qpel always incurs a significant cost in CPU decode time (+25% in
practice).
</p></li><li><p>
<span class="bold"><strong>psnr</strong></span>: does not affect the actual encoding,
but writes a log file giving the type/size/quality of each frame, and
prints a summary of PSNR (Peak Signal to Noise Ratio) at the end.
</p></li></ul></div><div class="itemizedlist"><p class="title"><b>Options not recommended to play with:</b></p><ul type="disc"><li><p>
<span class="bold"><strong>vme</strong></span>: The default is best.
</p></li><li><p>
<span class="bold"><strong>lumi_mask, dark_mask</strong></span>: Psychovisual adaptive
quantization.
You do not want to play with those options if you care about quality.
Reasonable values may be effective in your case, but be warned this is very
subjective.
</p></li><li><p>
<span class="bold"><strong>scplx_mask</strong></span>: Tries to prevent blocky
artifacts, but postprocessing is better.
</p></li></ul></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="menc-feat-mpeg4-lavc-example-settings"></a>14.3.4.Encoding setting examples</h3></div></div></div><p>
The following settings are examples of different encoding
option combinations that affect the speed vs quality tradeoff
at the same target bitrate.
</p><p>
All the encoding settings were tested on a 720x448 @30000/1001 fps
video sample, the target bitrate was 900kbps, and the machine was an
AMD-64 3400+ at 2400 MHz in 64 bits mode.
Each encoding setting features the measured encoding speed (in
frames per second) and the PSNR loss (in dB) compared to the "very
high quality" setting.
Please understand that depending on your source, your machine type
and development advancements, you may get very different results.
</p><p>
</p><div class="informaltable"><table border="1"><colgroup><col><col><col><col></colgroup><thead><tr><th>Description</th><th>Encoding options</th><th>speed (in fps)</th><th>Relative PSNR loss (in dB)</th></tr></thead><tbody><tr><td>Very high quality</td><td><tt class="option">vcodec=mpeg4:mbd=2:mv0:trell:v4mv:cbp:last_pred=3:predia=2:dia=2:vmax_b_frames=2:vb_strategy=1:precmp=2:cmp=2:subcmp=2:preme=2:qns=2</tt></td><td>6fps</td><td>0dB</td></tr><tr><td>High quality</td><td><tt class="option">vcodec=mpeg4:mbd=2:trell:v4mv:last_pred=2:dia=-1:vmax_b_frames=2:vb_strategy=1:cmp=3:subcmp=3:precmp=0:vqcomp=0.6:turbo</tt></td><td>15fps</td><td>-0.5dB</td></tr><tr><td>Fast</td><td><tt class="option">vcodec=mpeg4:mbd=2:trell:v4mv:turbo</tt></td><td>42fps</td><td>-0.74dB</td></tr><tr><td>Realtime</td><td><tt class="option">vcodec=mpeg4:mbd=2:turbo</tt></td><td>54fps</td><td>-1.21dB</td></tr></tbody></table></div><p>
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="custommatrices"></a>14.3.5.Custom inter/intra matrices</h3></div></div></div><p>
With this feature of
<a href="video-codecs.html#ffmpeg" title="7.1.1.FFmpeg/libavcodec"><code class="systemitem">libavcodec</code></a>
you are able to set custom inter (I-frames/keyframes) and intra
(P-frames/predicted frames) matrices. It is supported by many of the codecs:
<code class="systemitem">mpeg1video</code> and <code class="systemitem">mpeg2video</code>
are reported as working.
</p><p>
A typical usage of this feature is to set the matrices preferred by the
<a href="http://www.kvcd.net/" target="_top">KVCD</a> specifications.
</p><p>
The <span class="bold"><strong>KVCD "Notch" Quantization Matrix:</strong></span>
</p><p>
Intra:
</p><pre class="screen">
8 9 12 22 26 27 29 34
9 10 14 26 27 29 34 37
12 14 18 27 29 34 37 38
22 26 27 31 36 37 38 40
26 27 29 36 39 38 40 48
27 29 34 37 38 40 48 58
29 34 37 38 40 48 58 69
34 37 38 40 48 58 69 79
</pre><p>
Inter:
</p><pre class="screen">
16 18 20 22 24 26 28 30
18 20 22 24 26 28 30 32
20 22 24 26 28 30 32 34
22 24 26 30 32 32 34 36
24 26 28 32 34 34 36 38
26 28 30 32 34 36 38 40
28 30 32 34 36 38 42 42
30 32 34 36 38 40 42 44
</pre><p>
</p><p>
Usage:
</p><pre class="screen">
$ mencoder <em class="replaceable"><code>input.avi</code></em> -o <em class="replaceable"><code>output.avi</code></em> -oac copy -ovc lavc -lavcopts inter_matrix=...:intra_matrix=...
</pre><p>
</p><p>
</p><pre class="screen">
$ mencoder <em class="replaceable"><code>input.avi</code></em> -ovc lavc -lavcopts
vcodec=mpeg2video:intra_matrix=8,9,12,22,26,27,29,34,9,10,14,26,27,29,34,37,
12,14,18,27,29,34,37,38,22,26,27,31,36,37,38,40,26,27,29,36,39,38,40,48,27,
29,34,37,38,40,48,58,29,34,37,38,40,48,58,69,34,37,38,40,48,58,69,79
:inter_matrix=16,18,20,22,24,26,28,30,18,20,22,24,26,28,30,32,20,22,24,26,
28,30,32,34,22,24,26,30,32,32,34,36,24,26,28,32,34,34,36,38,26,28,30,32,34,
36,38,40,28,30,32,34,36,38,42,42,30,32,34,36,38,40,42,44 -oac copy -o svcd.mpg
</pre><p>
</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="menc-feat-dvd-mpeg4-example"></a>14.3.6.Example</h3></div></div></div><p>
So, you have just bought your shiny new copy of Harry Potter and the Chamber
of Secrets (widescreen edition, of course), and you want to rip this DVD
so that you can add it to your Home Theatre PC. This is a region 1 DVD,
so it is NTSC. The example below will still apply to PAL, except you will
omit <tt class="option">-ofps 24000/1001</tt> (because the output framerate is the
same as the input framerate), and of course the crop dimensions will be
different.
</p><p>
After running <tt class="option">mplayer dvd://1</tt>, we follow the process
detailed in the section <a href="menc-feat-telecine.html" title="14.2.How to deal with telecine and interlacing within NTSC DVDs">How to deal
with telecine and interlacing in NTSC DVDs</a> and discover that it is
24000/1001 fps progressive video, which means that we need not use an inverse
telecine filter, such as <tt class="option">pullup</tt> or
<tt class="option">filmdint</tt>.
</p><p>
Next, we want to determine the appropriate crop rectangle, so we use the
cropdetect filter:
</p><pre class="screen">mplayer dvd://1 -vf cropdetect</pre><p>
Make sure you seek to a fully filled frame (such as a bright scene), and
you will see in <span class="application">MPlayer</span>'s console output:
</p><pre class="screen">crop area: X: 0..719 Y: 57..419 (-vf crop=720:362:0:58)</pre><p>
We then play the movie back with this filter to test its correctness:
</p><pre class="screen">mplayer dvd://1 -vf crop=720:362:0:58</pre><p>
And we see that it looks perfectly fine. Next, we ensure the width and
height are a multiple of 16. The width is fine, however the height is
not. Since we did not fail 7th grade math, we know that the nearest
multiple of 16 lower than 362 is 352.
</p><p>
We could just use <tt class="option">crop=720:352:0:58</tt>, but it would be nice
to take a little off the top and a little off the bottom so that we
retain the center. We have shrunk the height by 10 pixels, but we do not
want to increase the y-offset by 5-pixels since that is an odd number and
will adversely affect quality. Instead, we will increase the y-offset by
4 pixels:
</p><pre class="screen">mplayer dvd://1 -vf crop=720:352:0:62</pre><p>
Another reason to shave pixels from both the top and the bottom is that we
ensure we have eliminated any half-black pixels if they exist. Note that if
your video is telecined, make sure the <tt class="option">pullup</tt> filter (or
whichever inverse telecine filter you decide to use) appears in the filter
chain before you crop. If it is interlaced, deinterlace before cropping.
(If you choose to preserve the interlaced video, then make sure your
vertical crop offset is a multiple of 4.)
</p><p>
If you are really concerned about losing those 10 pixels, you might
prefer instead to scale the dimensions down to the nearest multiple of 16.
The filter chain would look like:
</p><pre class="screen">-vf crop=720:362:0:58,scale=720:352</pre><p>
Scaling the video down like this will mean that some small amount of
detail is lost, though it probably will not be perceptible. Scaling up will
result in lower quality (unless you increase the bitrate). Cropping
discards those pixels altogether. It is a tradeoff that you will want to
consider for each circumstance. For example, if the DVD video was made
for television, you might want to avoid vertical scaling, since the line
sampling corresponds to the way the content was originally recorded.
</p><p>
On inspection, we see that our movie has a fair bit of action and high
amounts of detail, so we pick 2400Kbit for our bitrate.
</p><p>
We are now ready to do the two pass encode. Pass one:
</p><pre class="screen">mencoder dvd://1 -ofps 24000/1001 -oac copy -vf pullup,softskip,crop=720:352:0:62,hqdn3d=2:1:2 -ovc lavc \
-lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:mbcmp=3:autoaspect:vpass=1 \
-o Harry_Potter_2.avi</pre><p>
And pass two is the same, except that we specify <tt class="option">vpass=2</tt>:
</p><pre class="screen">mencoder dvd://1 -ofps 24000/1001 -oac copy -vf pullup,softskip,crop=720:352:0:62,hqdn3d=2:1:2 -ovc lavc \
-lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:mbcmp=3:autoaspect:vpass=2 \
-o Harry_Potter_2.avi</pre><p>
</p><p>
The options <tt class="option">v4mv:mbd=2:trell</tt> will greatly increase the
quality at the expense of encoding time. There is little reason to leave
these options out when the primary goal is quality. The options
<tt class="option">cmp=3:subcmp=3:mbcmp=3</tt> select a comparison function that
yields higher quality than the defaults. You might try experimenting with
this parameter (refer to the man page for the possible values) as
different functions can have a large impact on quality depending on the
source material. For example, if you find
<code class="systemitem">libavcodec</code> produces too much
blocky artifacting, you could try selecting the experimental NSSE as
comparison function via <tt class="option">*cmp=10</tt>.
</p><p>
For this movie, the resulting AVI will be 138 minutes long and nearly
3GB. And because you said that file size does not matter, this is a
perfectly acceptable size. However, if you had wanted it smaller, you
could try a lower bitrate. Increasing bitrates have diminishing
returns, so while we might clearly see an improvement from 1800Kbit to
2000Kbit, it might not be so noticeable above 2000Kbit. Feel
free to experiment until you are happy.
</p><p>
Because we passed the source video through a denoise filter, you may want
to add some of it back during playback. This, along with the
<tt class="option">spp</tt> post-processing filter, drastically improves the
perception of quality and helps eliminate blocky artifacts in the video.
With <span class="application">MPlayer</span>'s <tt class="option">autoq</tt> option,
you can vary the amount of post-processing done by the spp filter
depending on available CPU. Also, at this point, you may want to apply
gamma and/or color correction to best suit your display. For example:
</p><pre class="screen">mplayer Harry_Potter_2.avi -vf spp,noise=9ah:5ah,eq2=1.2 -autoq 3</pre><p>
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