mjpegtools.1

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.TH "MJPEG tools" "MJPEG Linux Square" "MJPEG tools manual"
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MJPEG HOWTO - An introduction to the MJPEG-toolsPraschinger Bernhardv1.48MJPEG capture/editting/replay and MPEG encoding toolset description

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Introduction


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I wrote this things down, because I had many sheets with notes on them.
This should be some kind of summary of collected knowledge of this sheets.
Andrew Stevens helped with encoding and VCD knowledge and hints.

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The mjpegtools are a set of programs that can do recording, playback, editing
and eventual MPEG compression of audio and video under Linux.

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Although primarily intended for use with capture / playback boards based on the
Zoran ZR36067 MJPEG codec chip, the mjpegtools can easily be used to process
and compress MJPEG video streams captured using xawtv using simple
frame-buffer devices.

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The HOWTO for the tools intended to give an an introduction to the MJPEG-tools
and the creation of MPEG 1/2 videos. VCD and SVCD, and the transcoding of 
existing mpeg streams.

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For more information about the programs read the corresponding man-page.

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Achtung es gibt auch eine deutsche Version bei:

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There is also a manpage of this text, you can read it with
\(rqman mjpegtools\(rq if installed. 

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The text version of this text is available via cvs, you should get it with a
tarball or the precompiled package (RPM and deb).

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In the following picture you see the typical workflow when you record a video.
Cut it afterwards and encode it. In the picture you also see the connections
to other programs. These parts are in grey, the parts in blue can be done with
the mjpegtools. 

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Video encoding workflow

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Unsorted list of useful Hints


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You have to compile and install the mjpeg_play package, for this read the
README & REQUIRED_SOFTWARE & INSTALL.
If you do not want to compile it, you can download the mjpeg .RPM or .DEB
package at Sourceforge.

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There is a script in the scripts/ directory. This script is something that
show's you a way how it can be done. It also creates (under certain
circumstances) videos that look quite good. Better videos you only get by
tuning the parameters yourself. 

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You will usually have to load the drivers for the Buz or DC10 or LML33 cards.So you have to run the update script providing as option the name of your card
you have. The script is usually in /usr/src/driver-zoran/.
The zoran kernel driver below the kernel 2.4.4 do not work.
You have to use the driver available from:

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The driver for the Matrox Marvel card also works, more information about it:

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If you compile the tools on a P6 based computer (PPro, P-II, P-III, P-4,
Athlon,Duron) then never try to let them run on a P5 based computer
(Pentium, Pentium-MMX, K6, K6-x, Cyrix, Via, Winchip). You'll get a 
\(rqillegal instruction\(rq and the program won't work.

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If lav2yuv dumps core then one possible cause is
no dv support was included. To enable it make sure that libdv is installed
on the system.  This will be necessary if you are using a digital camera 
(or analog to DV converter such as the Canopus ADVC100) and converting the 
dv avi format into the MPEG format.

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Start xawtv to see if you get an picture. If you want to use HW-playback of
the recorded streams you have to start xawtv (any TV application works) once
to get the streams played back. You should also check the settings of your
mixer in the sound card.

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If you compile the tools on a platform other than Linux not all tools 
will work.   Mjpegtools on a OS/X system for example will not have V4L
(video4linux) capability.

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Never try to stop or start the TV application when lavrec runs. If you start
or stop the TV application lavrec will stop recording, or your computer could
get \(rqfrozen\(rq\&. This is a problem of v4l (video4linux).

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This problem is solved with v4l2. If you use v4l2 you can record the video and stop and start the tv application whenever you want.
But v4l2 is currently (7. Jan. 2003) only supported for the zoran based cards (BUZ, DC10, DC10+, LML33) if you use the CVS driver from mjpeg.sf.net tagged with ZORAN_VIDEODEV_2.
And this driver only works with the 2.4.20 kernel and the 2.5.* development kernel.

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One last thing about the data you get before we start:

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.DS
.sp 
.ft RR
.nf
Audio: ( Samplerate * Channels * Bitsize ) / (8 * 1024)
CD Quality:(44100 Samples/sec * 2 Chanels * 16 Bit) / (8 * 1024)=172,2 kB/sec

The 8 * 1024 convert the value from bit/sec to kByte/sec

Video: (width * height * framerate * quality ) / (200 * 1024)
PAL HALF Size : (352 * 288 * 25 * 80) / (200 * 1024) = 990 kB/sec
PAL FULL size : (720 * 576 * 25 * 80) / (200 * 1024) = 4050 kB/sec
NTSC HALF size: (352 * 240 * 30 * 80) / (200 * 1024) = 990 kB/sec
NTSC FULL size: (720 * 480 * 30 * 80) / (200 * 1024) = 4050 kB/sec
.DE
.fi 
.ec
.ft P
.sp

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The 1024 converts the Bytes to kBytes. Not every card can record the size
mentioned. The Buz and Marvel G400 for example can only record a size of 
720x576 when using -d 1, the DC10 records a size of 384x288 when using -d 2.

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When you add audio and video datarate this is what your hard disk has to be 
able to write constantly streaming, else you will have lost frames.

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If you want to play with the \fB--mjpeg-buffer-size\fP\&. Remember the value 
should be at least big enough that one frame fits in it. The size of one frame 
is: (width * height * quality ) / (200 * 1024) = kB 
If the buffer is too small the rate calculation doesn't match any more and 
buffer overflows can happen. The maximum value is 512kB.

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How video works and the difference between the video types is explained here:

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There you also find how to create MPEG Still Images for VCD/SVCD.

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A good description of DV (Digital Video) can be found here:

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.SH Some books we found usefull


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written in English:
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Digital Video and HDTV by Charles Poyton (ISBN 1-55860-792-7)
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Digital Video Compression by Peter Symes (ISBN 0-07-142487-3)
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Video Demystified by Keith Jack (ISBN 1-878707-56-6)
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written in German:
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Fernsehtechnik von Rudolf Maeusl (ISBN 3-7785-2374-0)
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Professionelle Videotechnik - analoge und digitale Grundlagen von
U. Schmidt (ISBN 3-540-43974-9)
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Digitale Film- und Videotechnik von U. Schmidt (ISBN 3-446-21827-0)
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If you know some other really good book about that, write us!

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Recording videos


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.SH lavrec examples


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Recording with lavrec look's like this:

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\fB> lavrec -f a -i P -d 2 record.avi\fP

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Should start recording now,
.IP "-f a"
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use AVI as output format,
.IP "-i P"
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use as input source the SVHS-In with PAL format,
.IP "-d 2"
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the size of the pictures are half size (352x288)
.IP "record.avi"
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name of the created file.
.if \n(ll>1 .RE
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Recording is finished by pressing Crtl-C (nowadays: Strg-C). 
Sometimes using \fB-f A\fP instead of \fB-f a\fP might be necessary

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Other example:

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\fB> lavrec -f q -i n -d 1 -q 80 -s -l 80 -R l -U record.avi \fP

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Should start recording now, 
.IP "-f q"
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use Quicktime as output format, 
.IP "-i n"
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use Composite-In with NTSC format, 
.IP "-d 1"
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record pictures with full size (640x480) 
.IP "-q 80"
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set the quality to 80% of the captured image 
.IP "-s"
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use stereo mode (default mono) 
.IP "-l 80"
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set the recording level to 80% of the max during recording 
.IP "-R l"
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set the recording source to Line-In 
.IP "-U"
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With this lavrec uses the read instead of mmap for recording this is needed if your sound card does not
support the mmap for recording.
.if \n(ll>1 .RE
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Setting the mixer does not work with every sound card.  If you record with 2
different settings and both recordings are equally loud you should setup 
the mixer with a mixer program.  After that you should use the 
\fB-l -1\fP option when you record using lavrec

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The size of the image depends on the card you use.  At full size (-d 1)
you get these image sizes: BUZ and LML33: 720x576, the DC10: 768x576

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Other example:

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\fB> lavrec -w -f a -i S -d 2 -l -1 record%02d.avi\fP

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Should start recording,
.IP "-w"
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Waits for user confirmation to start (press enter) 
.IP "-f a"
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use AVI as output format, 
.IP "-i S"
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use SECAM SVHS-Input (SECAM Composite recording is also possible: -i s)
.IP "-d 2"
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the size of the pictures are half size
.IP "-l -1"
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do not touch the mixer settings
.IP "record%02d.avi"
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Here lavrec creates the first file named record00.avi after the file has reached a size of 1.6GB (after about 20 Minutes recording) it starts a new sequence named record01.avi and so on till the recording is stopped or the disk is full
.if \n(ll>1 .RE
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Other example:

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\fB> lavrec -f a -i t -q 80 -d 2 -C europe-west:SE20 test.avi\fP

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.IP ""
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Should start recording now, 
.IP "-f a"
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use AVI as output format, 
.IP "-i t"
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use tuner input, 
.IP "-q 80"
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set the quality to 80% of the captured image 
.IP "-d 2"
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the size of the pictures are half size (352x288) 
.IP "-C"
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choose TV channels, and the corresponding -it and -iT (video source:
TV tuner) can currently be used on the Marvel G200/G400 and the Matrox
Millenium G200/G400 with Rainbow Runner extension (BTTV-Support is under
construction). For more information on how to make the TV tuner parts of these
cards work, see the Marvel/Linux project on:
.if \n(ll>1 .RE
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Last example:

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\fB> lavrec -f a -i p -g 352x288 -q 80 -s -l 70 -R l --software-encoding
test03.avi\fP

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The two new options are \fB-g 352x288\fP, which sets the size of the
video to be recorded when using \fB--software-encoding\fP, this enables
the software encoding of the recorded images. With this option you can also
record from a bttv based card. The processor load is high. This option only
works for generic video4linux cards (such as the brooktree-848/878 based 
cards), it doesn't work for zoran-based cards.

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.SH Other recording hints


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All lavtools accept a file description like file*.avi, so you do not have
to name each file, but that would also be a posibillity to do. 

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Note: More options are described in the man-page, but with this you should be able to get started.

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Here are some hints for sensible settings. Turn the quality to 80%
or more for -d 2 capture. At full resolution as low as 40% seems to
be visually \(rqperfect\(rq\&. -d 2 is already better than VHS video
(a *lot*!). For a Marvel you should not set the quality higher than 50 when
you record at full size (-d 1). If you use higher settings (-q 60) it is
more likely that you will encounter problems. Higher settings
will result in framedrops. 
If you're aiming to create VCD's then there is little to be gained