mjpegtools.1

来自「Motion JPEG编解码器源代码」· 1 代码 · 共 2,296 行 · 第 1/5 页

First there is some general description in the encoding process and afterwards
there is a detailed description of some commonly used output formats. 

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If you want a one command conversation to mpeg videos try lav2mpeg in
the scripts directory

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The encoding with the lav2mpeg script looks like this for mpeg1 output:

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\fB>lav2mpeg -a 160 -b 2110 -d 320x240 -m mpeg1 -o output.mpg file.eli\fP

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.nr ll +1
.nr t\n(ll 0
.if \n(ll>1 .RS
.nr bi 1
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Will create a mpeg1 with videobitrate of 2110kBit/sec and audiobitrate of 
160 kBit/sec
.nr bi 1
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at a resolution of 320x240
.if \n(ll>1 .RE
.nr ll -1

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Or for the generation of mpeg2 output:

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\fBlav2mpeg -o mpeg2 -O output.mpg file.eli\fP

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.nr ll +1
.nr t\n(ll 0
.if \n(ll>1 .RS
.nr bi 1
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Will create a mpeg2 with default bitrate in same resolution as the input
resolution
.if \n(ll>1 .RE
.nr ll -1

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Better results can be accomplished, however, by trying various options
and find out which ones work best for you. These are discussed below.

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The creation of MPEG1 movies is explained with more examples and in
greater detail because most of the things that can be used for MPEG1 also work 
for the other output formats

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For the creation of of VCD/SVCD Stills sequences (-f 6, -f 7 in mpeg2enc) you
should see:

Still sequences are needed for the creation of menus in VCD/SVCD. The
creation of menus is described in the doku of vcdimager.

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.SH Creating sound


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MPEG-1 videos need MPEG1-layer2 sound files. For MPEG-2 videos you can
use MPEG1-Layer2 and MPEG1-Layer3 (MP3).    Layer 3 (MP3) audio is not an
offically valid audio format but many VCD players will recognize it.   MP3
audio is not valid for DVDs.
You should stick to MPEG1-Layer2 because most of the MPEG2 players
(DVD Player for example usually the different Winxx Versions have
great problems with this too) are not able to play MPEG2-Video and
MPEG1-Layer3 sound.

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mp2enc is a MPEG1-layer 2 Audio encoder. The toolame encoder is also able
to produce an layer 2 file. You can use that one as well.   Toolame is much
faster than mp2enc but toolame does not peform resampling (48000 to 44100
samples/second).  Many hardware players will play SVCDs using 48000 rate
audio.  For mp3 creation I'm be sure you have an encoder.

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Example:

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\fB> lav2wav stream.avi \(br mp2enc -o sound.mp2\fP

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This creates a mpeg sound file out of the stream.avi with 224kBit/sec
bitrate and a sample rate of 48kHz. If you audio file has 44.1kHz mp2enc
resamples the audio to create a 48kHz output. If you want a 44.1kHz 
output sample rate you have to add -r 44100 to the mp2enc command

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Example

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\fB> cat sound.wav \(br mp2enc -v 2 -V -o sound.mp2\fP

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This creates a VCD (-V bitrate=224, stereo, sampling rate:44100)
compatible output from the wav file.

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With -v 2 mp2enc is more verbose, while encoding you see the number of sec of
audio already encoded.

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You can test the output with:

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\fB> plaympeg sound.mp2\fP

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\fBNOTE:\fP plaympeg is a MPEG1 Player for Linux, you can use other players
as well, for MPEG audio testing you can also use mpg123.

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.SH Converting video


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You can create MPEG1 and MPEG2 videos.

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Normally the first video you create is not the best. For optimal
quality/size you need to play with the bitrate, search radius, noise
filter .... The options of mpeg2enc are described in the manpage of
mpeg2enc.

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Example:

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\fBlav2yuv stream.avi stream1.avi \(br mpeg2enc -o video.m1v\fP

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This creates an video file with the default constant bitrate of 1152kBit/sec.
This is the bitrate you need if you want to create VCDs. You can specify more
files and also use the placeholder %nd. Where \fBn\fP describes
the number.

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Example:

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\fB> lav2yuv streami%02d.avi \(br mpeg2enc -b 1500 -r 16 -o video.m1v\fP

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mpeg2enc creates a video with a bitrate of 1500kBit/s uses
an search radius of 16. That means when trying to find similar 16*16
macroblocks of pixels between frames the encoder looks up to 16
pixels away from the current position of each block. It looks twice as
far when comparing frames 1 frame apart and so on. Reasonable values
are 16 or 24. The default is 16 so adding the option here is silly.
Lower values (0, 8), improve the encoding speed but you get lower
quality (more visible artifacts) while higher values (24, 32) improve the
quality at the cost of the speed. With the file description of
stream%02d.avi all files are processed that match this pattern
with 00, 01....

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Scaling


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Using yuvscaler one can now also scale the video before encoding it.
This can be useful for users with a DC10 or DC10+ cards which captures
at -d 1 768x576 or -d 2 384x288 (PAL/SECAM) or -d 1 640x480 (NTSC).

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You get a full description of all commands by reading the manpage or running:

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\fB>yuvscaler -h\fP

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Example:

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\fB> lav2yuv stream.avi \(br yuvscaler -O VCD \(br mpeg2enc -o video.m1v\fP

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This will scale the stream to VCD size which for PAL/SECAM is 352x288 and
for NTSC is 352x240. The scaled yuvstream is encoded to MPEG-1.

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It can also do SVCD scaling to 480x480 (NTSC) or 480x576 (PAL/SECAM):

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\fB> lav2yuv stream.avi \(br
yuvscaler -O SVCD -M BICUBIC \(br mpeg2enc -o video.m1v\fP

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The mode keyword (-M) forces yuvscaler to use the higher quality
bicubic algorithms for downscaling and not the default resample
algorithms. Upscaling is always done using the bicubic algorithm.

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Example

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\fB> lav2yuv stream.avi \(br yuvscaler -I USE_450x340+20+30
-O SIZE_320x200 \(br mpeg2enc -o video.m1v \fP

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Here we only use a part of the input and specify a nonstandard output 
resolution.

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\fBNOTE:\fP yuvscaler can set a active area, and set everything else to
black using: -I ACTIVE_WidthxHeight+WidthOffset+HeightOffset 

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Testing is done by:

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\fB> plaympeg video.m1v\fP

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\fBNOTE:\fPThese are only examples. There are more options you can use. You
can use most of them together to create high quality videos with the
lowest possible bitrate.

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\fBNOTE2:\fPThe higher you set the search radius the longer the conversion
will take. In general the more options used the longer encoding takes.

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\fBNOTE3:\fPMPEG1 was not designed to be a VBR (variable bitrate stream) !!
So if you encode with -q 15 mpeg2enc sets the maximal bitrate -b to
1152. If you want a VBR MPEG1 you have to set -b very high (2500).

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\fBNOTE4:\fPMaybe you should give better names than video.mpg. A good idea
is to use the options as part of the filename
(for example: \fBvideo_b1500_r16_41_21.m1v\fP).
Another possibility is to call all the layer 2 files \(rq\&.mp2\(rq all the
MPEG-1 video files \(rq\&.m1v\(rq and all MPEG-2 video files 
\(rq\&.m2v\(rq Easy to see what's happening then. Reserve .mpg for
multiplexed MPEG-1/2 streams.

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.SH Putting the streams together


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Example:

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\fB> mplex sound.mp2 video.m1v -o my_video.m1v\fP

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Puts the sound.mp2 and the video.m1v stream together to my_video.mpg

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Now you can use your preferred MPEG player and watch it. All players (gtv for
example) based on the SMPEG library work well for MPEG-1. Other players 
(which can play MPEG-2 as well as MPEG-1 movies) are: xmovie, xine, and 
MPlayer.

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\fBNOTE:\fP If you have specified the \fB-S\fP option for mpeg2enc
mplex will automatically split the files if there is in the output filename
a %d (looks like: -o test%d.mpg) The files generated this way
are separate stand-alone MPEG steams!

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\fBNOTE2:\fP xine might have a problem with seeking through videos.
mplayer has a problem with the \(rqseek backward/forward\(rq with 
variable bitrate streams because it goes forward in the file the amount of
data for a constant bitrate stream. That amount might be significantly more
than 10 seconds or one minute (those are the amount mplayer seeks for each
press of the arrow keys). So don't wonder if it seeks much more time
forward or backward than you expect.

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\fBVariable bit-rate multiplexing:\fP
Remember to tell mplex you're encoding VBR (-V option) as well as
mpeg2enc (see the example scripts). It *could* auto-detect but it is not
working yet. You should tell mplex a video buffer size at least as large
as the one you specified to \(rqmpeg2enc\(rq Sensible numbers for
MPEG-1 might be a ceiling bit-rate of 2800Kbps, a quality ceiling
(quantization floor) of 6 and a buffer size of 400K.

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Example:

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\fB> mplex -V -r 1740 audio.mp2 video_vbr.m1v -o vbr_stream.mpg\fP

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Here we multiplex a variable bitrate stream. mplex is now a single
pass multiplexer so it can't detect the maximal bitrate and we have to
specify it. The data rate for the output stream is: audio bitrate +  
peak videobitrate + 1-2% for mplex information. If audio (-b 224) has
224kBit, video has 1500kBit (was encoded with -b 1500 -q 9) then we
have 1724 * 1.01 or about 1740kBit.

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Example:

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\fB> plaympeg my_video.mpg\fP

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oder

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\fB> gtv my_video.mpg\fP
.SH Creating MPEG1 Videos


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For MPEG1 you can use mpeg layer 2 Audio and mpeg1 video. A subset of
MPEG1 movies are VCD's. You can use VBR (Variable BitRate) for the
Video (although VCDs are almost always use CBR video) but the Audio has to 
be CBR (Constant BitRate).

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MPEG1 is recommended for picture sizes up to 352x288 for PAL and
352x240 for NTSC for larger sizes MPEG2 is the better choice.
There is no exact resolution where MPEG1 is better than MPEG2.
Just to make soure, MPEG1 can't handle interlaced sources. If you video
is interlaced you need MPEG2 to get it proper encoded. .

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MPEG1 Audio creation Example


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\fB> lav2wav editlist.eli \(br mp2enc -r 44100 -o sound.mp2\fP

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You can save some bits by telling
mp2enc to use a lower bitrate (-b option) like 160 or 192 kBit/s.
The -r 44100 option forces mp2enc to generate a 44.1kHz audio file.

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\fB> lav2wav editlist.eli \(br mp2enc -b 128 -m -o sound.mp2\fP

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This creates a mono output with an bitrate of 128kBit/sec bitrate.   
The input this time is the editlistfile (can have any name) created  
with glav so all changes you made in glav are direct processed and   
handed over to mp2enc.  You do NOT have to create an edited stream
with lavtrans to get it converted properly.

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MPEG1 Video creation Example


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\fB> lav2yuv editlist.eli \(br mpeg2enc -b 2000 -r 24 -q 6 -o video.m1v\fP

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mpeg2enc creates an video with an bitrate of 2000kBit/s (or
2048000Bit/s) but the -q flag activates the variable bitrate and a
quality factor of 6. It uses a search radius of 24.

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\fBExplanation:\fPwhen mpeg2enc is invoked without the 'q'
flag it creates \(rqconstantbit-rate\(rq MPEG streams. Where (loosely
speaking) the strength of compression (and hence picture quality) is
adjusted to ensure that on average each frame of video has exactly the
specified number of bits. Such constant bit-rate streams are needed for
broadcasting and for low-cost hardware like DVD and VCD players which use
slow fixed-speed player hardware.

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Obviously this is fairly inefficient as it means inactive scenes use
up bits that could better be \(rqspent\(rq on rapidly changing scenes.
Setting the 'q' flag tells mpeg2enc to generate variable bit-rate
streams. For such streams the bit-rate specified is simply the maximum
permissible. The 'q' parameter specifies the minimum degree of
compression to be applied by specifying how exactly picture
information is recorded. Typically, 'q' would be set so that quiet
scenes would use less than the specified maximum (around 6 or 8) but
fast moving scenes would still be bit-rate limited. For archival
purposes setting a maximum bit-rate high enough never to be reached
(e.g. 10Mbps) and a q of 2 or 3 are reasonable choices.

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Example:

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\fB> lav2yuv stream.avi \(br yuvscaler -I ACTIVE_352x240+0+24
\(br mpeg2enc -b 1152 -r 16 -4 1 -2 1 -o video.m1v\fP

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Usually there is at the top and at the bottom a nearly black border
and a lot of bandwidth is used for something you do not like. The
yuvscaler -I ACTIVE option sets everything that is not in the
described area to black, but the imagesize (352x288) is not changed.
So you have a real black border the encoder only uses a few bits for
encoding them. You are still compatible with the VCD's format in this example.
To determine the active window extract one frame to the jpeg format:

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\fB> lavtrans -f i -i 100 -o frame.jpg test.avi\fP

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Than use your favorite graphic display program to determine the active size.
The -4 1 and -2 1 options improves the quality about 10% but conversion
is slower.

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At the size of 352x288 (1/2 PAL size, created when using the -d 2 
option when recording) the needed bitrate is/should be between 1000 -
1500kBit/s. For NTSC it should be about the same, because the image is smaller,
but there are more frames per second than in PAL.

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Anyways, the major factor is quality of the original and the degree of
filtering. Poor quality unfiltered material typically needs a higher
rate to avoid visible artifacts.
If you want to reduce bit-rate without annoying artifacts when
compressing broadcast material you should try one (or more) of the noise 
filters.

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Example:

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\fB> lav2yuv stream.avi \(br mpeg2enc -b 1500 -n s -g 6 -G 20 -P -o
video.m1v\fP

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Here the stream.avi will be encoded with:

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.nr ll +1
.nr t\n(ll 2
.if \n(ll>1 .RS
.IP "-b 1500"
.nr bi 1

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a Bitrate of 1500kBit/sec
.IP "-n s"
.nr bi 1

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the input Video norm is forced to SECAM