lavpipe(1)
NAME
lavpipe - creates raw YUV streams from pipe list scripts
SYNOPSIS
lavpipe [-o num] [-n num] pipe-list
DESCRIPTION
lavpipe reads a little script file that I called 'pipe
list' and that is of a similar structure as the edit lists
that can be fed into lav2yuv (for info about the pipe list
format see below).
The pipe list defines several video sources and filters
that are combined by lavpipe to produce a single output
YUV stream on stdout (which for example can be compressed
and stored to disk via mpeg2enc(1) or yuv2lav(1)).
OPTIONS
The command line options allow to only output a specific
part of the resulting video stream, that means you can
tell lavpipe how many frames to skip and how many frames
to deliver from that point on.
- -o num This is the frame offset of the output video. The
- first num frames of the resulting video simply are
neither calculated nor written to stdout. This
value defaults to 0. - -n num This is the frame count. If the input files or
- streams defined in the pipe list script are long
enough, the output will be of exactly num frames
length. A value of 0 means that all frames until
the last one as defined in the pipe list will be
written out, as long as there's some input (0 is
the default). - pipe-list
- This is name of the pipe list file that lavpipe
will 'execute'. For information about this file's
format see below. - -? Display a synopsis of the command syntax.
EXAMPLES
- lavpipe -o 100 -n 25 film.pli
- would calculate and output to stdout frames 100 to
124 as defined in film.pli (in PAL this would be
the 5th second of the film). - lavpipe input.pli | yuv2lav -q80 output.avi
- would save the movie assembled by lavpipe as a sin
gle AVI file.
USAGE
In this section the format of lavpipe's input files, the
pipe list scripts is explained. If you need some examples
or a more detailed tutorial, please read the mjpegtools(1)
manpage's section about CREATING MOVIE TRANSITIONS. and
the file README.lavpipe that should be included in the
distribution. Also feel free to contact us via the mail
ing list (see below).
A pipe list contains of two parts: the YUV source list and
after this, as many sequence descriptions as wanted. It
always begins with the following two lines:
- LAV Pipe List
- This is the first line in every pipe list script.
It is used as a simple test if lavpipe really was
given a pipe list script and not your PhD thesis as
input. - NTSC|PAL
- This is the second line in every pipe list and can
be either PAL or NTSC, depending on what video
standard you use. I don't remember if this is used
at the moment. - Now follows the source list:
- num This is the number of input commands. lavpipe will
- read the next num lines and interpret them as input
stream commands. - command (num times)
- This is a valid command line with two variables $o
and $n that will be replaced by lavpipe with the
offset and number of frames that the program has to
output. Example:
lav2yuv -o $o -f $n input.avi - Thus, an example source list could look like this:
2
lav2yuv -o $o -f $n scene1.avi lav2yuv -o $o -f $n scene2.avi - And after this you can append as many sequence descrip tions as needed. Each of them is built up as follows:
- num The number of frames that this sequence will last.
- num The number of inputs that will be used in this
- sequence. This number must of course be less than
or equal to the number of inputs that are defined
above. - idx [ofs] (num times)
- These are the indices to the sources that are
defined at the beginning of the file (first source
is 0) with an optional frame offset (i.e. sequence
starts with frame number ofs of this input.) - this
value defaults to 0. Example:
0 150 - command
- This is a valid command line to a YUV filter tool
that reads num input streams and writes one output
stream, combining its inputs. Optionally, the fil
ter tool can be given the two $o and $n variables
that will be replaced by lavpipe as in the source
commands (see above). For further info read
README.lavpipe or the documentation for the filter programs (if available). An example filter could
look like this:
transist.flt -o 0 -O 255 -s $o -n $n -d 50 And if the sequence only has one input that simply
should be copied to the output, you can use a dash
instead of a command line:
- And here's an example for a complete pipe list that imple
ments a transistion from scene1.avi to scene2.avi (remove
the comments after #): - LAV Pipe List
PAL
2
lav2yuv -o $o -f $n scene1.avi lav2yuv -o $o -f $n scene2.avi 50 # first sequence: 50 frames
1 # contains one input:
0 0 # scene1.avi, offset 0
- # simple output
25 # second sequence: 25 frames
2 # contains two inputs:
0 50 # scene1.avi, offset 50
1 # scene2.avi, offset 0
transist.flt -o 0 -O 255 -s $o -n $n -d 50 # transistion 50 # third sequence: 50 frames
1 # contains one input:
1 25 # scene2.avi, offset 25
- # simple output
BUGS
I'm sure there are enough of them. lavpipe often accepts
malformed pipe lists and then writes out a video that was
all but intended - without warning.
NOTES
There are also some serious limitations in the system,
such as frame-by-frame processing. But as the goal when
writing lavpipe was the simplicity of the pipeline, other
tools will have to be written to do more interesting
tasks.
But I want to note that it is very well possible to write
a pipe list that combines several files, and then use that
pipe list as an input for another pipe list by simply
using the lavpipe command in the source list (see above) this can be already used to do some nice things, if you
have some nice filters.
AUTHOR
- This man page was written by pHilipp Zabel.
If you have questions, remarks, problems or you just want
to contact the developers, the main mailing list for the
MJPEG-tools is: - mjpeg-users@lists.sourceforge.net
- For more info, see our website at
- http://mjpeg.sourceforge.net