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Full Discussion: Running ffmpeg in loop seems to change reading from file
Top Forums Shell Programming and Scripting Running ffmpeg in loop seems to change reading from file Post 302623737 by agama on Saturday 14th of April 2012 01:04:24 PM
Old 04-14-2012
My guess is that ffmpeg is reading two bytes from stdin. If you are using, or can use, kshell, then you can avoid that with code like this:

Code:
#!/bin/ksh

exec {fd}<data-file      # open the file assign file descriptor to fd
while read -u $fd buf   # read from fd rather than stdin
do
    echo $buf
    #ffmpeg-command and parms
done
<&$fd-      # close the file



The while reads from the file descriptor opened by the exec statement and assigned to fd and thus isn't affected by what anything in the loop might read from stdin.

If you need to, or would rather use bash, then you'll have to specifically pick a file descriptor to use:

Code:
fd=11
exec 11<data-file        # open the file assign file descriptor to fd
while read -u $fd buf   # read from fd rather than stdin
do
    echo "$buf $foo"
    ffmpeg-command here
done
<&$fd-      # close the file



And, from my small bit of testing, you have to supply a hard number on the exec when using bash, this seems not to work: exec $fd<data-file

---------- Post updated at 13:04 ---------- Previous update was at 12:58 ----------

Kludgy, but this would work allowing the variable contents to be used when opening:

Code:
fd=9
eval exec $fd\<data-file

This User Gave Thanks to agama For This Post:
Thriceguy
 

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LEARN ABOUT DEBIAN

pfsoutffmpeg

pfsoutffmpeg(1) 					      General Commands Manual						   pfsoutffmpeg(1)

NAME

       pfsoutffmpeg - Read pfs frames from stdin and forward them to ffmpeg program

SYNOPSIS

       pfsoutffmpeg [--help] <ffmpeg options> output_file

DESCRIPTION

       This command is a wrapper for ffmpeg program and can be used to write pfs frames to a compressed video.

       Check the examples section to for sample usage and see manual of ffmpeg for further information.

       Note  that  the	usage  of '-f' switch (input format specifier) and '-i' switch (input file specifier) of the ffmpeg program is implemented
       inside the script and is therefore not allowed.

EXAMPLES

       pfsinrgbe frame%04d.hdr --frames 100:2:200 | pfstmo_reinhard02 -s
	      | pfsgamma -g 1.7 | pfsoutffmpeg -qscale 4 test.avi

	      1. Read HDR frames in RGBE format with the following names:
		 frame0100.hdr, frame0102.hdr, frame0104.hdr,... frame0200.hdr

	      2. Apply local tone mapping operator to each frame (Reinhard2002
		 model, part of the PFSTMO package)

	      3. Apply gamma correction to each tone mapped frame

	      4. Compress frames to test.avi animation

SEE ALSO

       ffmpeg(1) pfsin(1) pfstmo_reinhard02(1) pfsgamma(1)

BUGS

       Frames smaller than 512x384 can cause broken pipe error, due to bug in ppm pipe reading routine in ffmpeg.

       Please report bugs and comments to Rafal Mantiuk <mantiuk@mpi-sb.mpg.de> or Grzegorz Krawczyk <krawczyk@mpi-sb.mpg.de>.

																   pfsoutffmpeg(1)
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