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This file describes how to make a transistion from one video file
to another using the current sample implementations.
Especially ypipe will be replaced (hopefully) soon by a more
capable program.
The programs involved in this process are:
- lav2yuv, which decompresses the given input files (or any portions
of them) and gives us raw yuv frame streams that can be
piped through the several tools.
- ypipe, which starts two instances of lav2yuv and combines the two
input streams into one, in which every even frame is from
the first and every odd frame from the second input.
- transist.flt, which takes the frame-interlaced stream from
ypipe and writes out the final transistion.
- yuv2lav or mpeg2enc, which compress the resulting yuv stream
into an mjpeg or mpeg file.
Let's assume simple this scenery: We have two input videos, intro.avi
and epilogue.qt and want make intro.avi transist into epilogue.qt
with a duration of one second (that is 25 frames for PAL or 30 frames
for NTSC).
intro.avi and epiloque.qt have to be of the same format regarding
frame rate and image resolution, at the moment.
In this example they are both 352x288 PAL files. intro.avi contains
250 frames and epilogue.qt is 1000 frames long.
Therefor our output file will contain:
- the first 225 frames of intro.avi
- a 25 frame transistion containing the last 25 frames of intro.avi
and the first 25 frames of epilogue.qt
- the last 975 frames of epilogue.qt
We could get the last 25 frames of intro.avi by calling:
lav2yuv -o 225 -f 25 intro.avi
(-o 225, the offset, tells lav2yuv to begin with frame # 225
and -f 25 makes it output 25 frames from there on)
Another possibility is:
lav2yuv -o -25 intro.avi
(negative offsets are counted from the end)
And the first 25 frames of epilogue.qt:
lav2yuv -f 25 epilogue.qt
(-o defaults to an offset of zero)
But we need to combine the two streams with ypipe. So the call would be:
ypipe "lav2yuv -o 255 -f 25 intro.avi" "lav2yuv -f 25 epilogue.qt"
The output of this is a raw yuv stream that can be fed into
transist.flt.
transist.flt needs to be informed about the duration of the transistion
and the opacity of the second stream at the beginning and at the end
of the transistion:
-o num opacity of second input at the beginning [0-255]
-O num opacity of second input at the end [0-255]
-d num duration of transistion in frames
An opacity of 0 means that the second stream is fully transparent
(only stream one visible), at 255 stream two is fully opaque.
In our case the correct call (transistion from stream 1 to stream 2)
would be:
transist.flt -o 0 -O 255 -d 25
The -s and -n parameters equal to the -o and -f parameters of lav2yuv
and are only needed if anybody wants to render only a portion of the
transistion for whatever reason. Please note that this only affects
the weighting calculations - none of the input is really skipped, so
that if you pass the skip parameter (-s 30, for example), you also
need to skip the first 30 frames in lav2yuv (-o 30) in order to get
the expected result. If you didn't understand this, send an email to
the authors or simply ignore -s and -n.
The whole procedure will be automated later, anyway.
Now we want to compress the yuv stream with yuv2lav.
yuv2lav -f a -q 80 -o transistion.avi
Reads the yuv stream from stdin and outputs an avi file (-f a)
with compressed jpeg frames of quality 80.
Now we have the whole command for creating a transistion:
ypipe "lav2yuv -o 255 -f 25 intro.avi" "lav2yuv -f 25 epilogue.qt" | \
transist.flt -o 0 -O 255 -d 25 | yuv2lav -f a -q 80 -o transistion.avi
(This is one line.) The resulting video can be written as a LAV Edit List,
a plain text file containing the following lines:
LAV Edit List
PAL
3
intro.avi
transistion.avi
epilogue.qt
0 0 224
1 0 24
2 25 999
This file can be fed into xlav or lavplay, or you
can pipe it into mpeg2enc with lav2yuv or combine
the whole stuff into one single mjpeg file with
lavtrans or lav2yuv|yuv2lav.
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