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Full Discussion: Input redirection script
Top Forums Shell Programming and Scripting Input redirection script Post 302968194 by Don Cragun on Saturday 5th of March 2016 02:52:42 AM
Old 03-05-2016
I'm not sure I'm following what is going on here, but I think you want something more like:
Code:
#!/bin/bash
rm -f /tmp/pipe
mkfifo /tmp/pipe
./yuv4mpeg_to_v4l2 < /tmp/pipe &
while [ 1 ]
do
  mplayer tom_and_jerry.mp4 -vf scale=480:360 -vo yuv4mpeg:file=/tmp/pipe
  sleep 65;
done > /tmp/pipe

This assumes that yuv4mpeg_to_v4l2 is reading data from standard input and feeding it into your display device while mplayer is converting tom_and_jerry.mp4 into a format that yuv4mpeg_to_v4l2 reads and directs its output to the file named by the -vo yuv4mpeg:file=pathname option's option argument.

It also assumes that mplayer does not write anything to its standard output (and that nothing else inside the while loop writes anything to standard output). The FIFO has to be kept open by something on both the read end (which is being done by yuv4mpeg_to_v4l2) and on the write end (which I am doing with the redirection on the while loop). If mplayer is the only thing writing to the FIFO, the write end will close after mplayer finishes the conversion once and yuv4mpeg_to_v4l2 will see an EOF.
 

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PIPE(2) 							System Calls Manual							   PIPE(2)

NAME
pipe - create an interprocess channel SYNOPSIS
#include <u.h> #include <libc.h> int pipe(int fd[2]) DESCRIPTION
Pipe creates a buffered channel for interprocess I/O communication. Two file descriptors are returned in fd. Data written to fd[1] is available for reading from fd[0] and data written to fd[0] is available for reading from fd[1]. After the pipe has been established, cooperating processes created by subsequent fork(2) calls may pass data through the pipe with read and write calls. The bytes placed on a pipe by one write are contiguous even if many processes are writing. Write boundaries are preserved: each read terminates when the read buffer is full or after reading the last byte of a write, whichever comes first. The number of bytes available to a read(2) is reported in the Length field returned by fstat or dirfstat on a pipe (see stat(2)). When all the data has been read from a pipe and the writer has closed the pipe or exited, read(2) will return 0 bytes. Writes to a pipe with no reader will generate a note sys: write on closed pipe. SOURCE
/sys/src/libc/9syscall SEE ALSO
intro(2), read(2), pipe(3) DIAGNOSTICS
Sets errstr. BUGS
If a read or a write of a pipe is interrupted, some unknown number of bytes may have been transferred. When a read from a pipe returns 0 bytes, it usually means end of file but is indistinguishable from reading the result of an explicit write of zero bytes. PIPE(2)
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