#!/bin/sh
##
## SCRIPT: movieFilePROPERTIES_ffmpeg-i.sh
##
##+#######
## PURPOSE:
## This script runs the 'ffmpeg -i' command on a filename which is provided
## to this script as its only argument.
##
## This script is meant to return several lines selected from the output
## of 'ffmpeg -i'. The lines are to be sent to standard out.
##
## Those selected lines are to provide the 'properties' of a movie file.
## Example lines to be extracted:
##
## Input #0, mpeg, from 'ParkingTechnique2_320x240_12sec_MPEG1-MP2.mpeg':
##   Duration: N/A, start: 0.602367, bitrate: N/A
##     Stream #0.0[0x1e0]: Video: mpeg1video, yuv420p, 320x240 [PAR 178:163 DAR 712:489], 500 kb/s, 29.97 tbr, 90k tbn, 29.97 tbc
##     Stream #0.1[0x1c0]: Audio: mp2, 44100 Hz, mono, s16, 96 kb/s
##
##+#########
## CALLED BY:
## This shell script is meant to be called from the Tk GUI 'wrapper'
## script --- 'movieClipCropEtc_ffmpeg_FrontEnd.tk' --- when the
## user requests the PROPERTIES of an input or output movie file.
##
##+######
## METHOD:
## It would be nice to simply call 'ffmpeg -i' via a Tcl 'exec' command
## in the Tk script. However, the 'ffmpeg -i' command throws an error
## when output is not directed to a recognized media file type ---
## and all text output goes to 'stderr' not 'stdout'.
##
## Sample output follows:
##
## $ ffmpeg -i ParkingTechnique2_320x240_12sec_MPEG1-MP2.mpeg
## FFmpeg version SVN-r19352-4:0.5+svn20090706-2ubuntu2.3, Copyright (c) 2000-2009 Fabrice Bellard, et al.
##   configuration: --extra-version=4:0.5+svn20090706-2ubuntu2.3 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --extra-cflags=-I/build/buildd/ffmpeg-0.5+svn20090706/debian/include --enable-shared --disable-static
##   libavutil     49.15. 0 / 49.15. 0
##   libavcodec    52.20. 0 / 52.20. 0
##   libavformat   52.31. 0 / 52.31. 0
##   libavdevice   52. 1. 0 / 52. 1. 0
##   libavfilter    0. 4. 0 /  0. 4. 0
##   libswscale     0. 7. 1 /  0. 7. 1
##   libpostproc   51. 2. 0 / 51. 2. 0
##   built on Mar 31 2011 18:50:18, gcc: 4.4.1
## Input #0, mpeg, from 'ParkingTechnique2_320x240_12sec_MPEG1-MP2.mpeg':
##   Duration: N/A, start: 0.602367, bitrate: N/A
##     Stream #0.0[0x1e0]: Video: mpeg1video, yuv420p, 320x240 [PAR 178:163 DAR 712:489], 500 kb/s, 29.97 tbr, 90k tbn, 29.97 tbc
##     Stream #0.1[0x1c0]: Audio: mp2, 44100 Hz, mono, s16, 96 kb/s
## At least one output file must be specified
##
## NOTE: The information we want is between the 'built on' line and the
## ending error message line: 'At least one output file must be specified'.
##
## There does not appear to be a way to direct these information messages and
## the ending error message to 'stdout' (even with '2>&1') in such a way that
## the Tk script does not detect an error. When Tk detects the error return code,
## there does not seem to be a way to pass 'stdout' to the Tk script.
##
## So we call on this 'external' shell script from the Tk script,
## to do the dirty work of extracting the desired lines from
## the stderr output and pass the lines back to the Tk script
## without throwing an error that would prevent the Tk script
## from accepting the lines sent to stdout.
##
## We use '2>&1' to pipe the output of 'ffmpeg -i' to a small
## 'awk' program that extracts the desired lines --- between
## the 'built on' line and the 'At least one ...' line.
##
## Since we let the output of 'awk' go to 'stdout', that becomes
## the output from this script that will be captured in the Tk script.
##
## NOTE: Piping the output of 'ffmpeg -i <filename> 2>&1' to
##          egrep 'Input|Duration|Stream'
## might work, but it may miss some output for some kinds of media/movie files.
##
##+#########
## REFERENCE:
## http://www.commandlinefu.com/commands/view/2207/get-video-information-with-ffmpeg
## 2009-05-18 
## TOPIC: Get video information with ffmpeg
##
## $ ffmpeg -i filename.flv
##
## I used an flv in my example, but it'll work on any file ffmpeg supports.
##
## It says it wants an output file [the 'At least one output' error message],
## but it tells what you want to know without one [without specifying an
## output file].
##
## Also see:
## http://stackoverflow.com/questions/11400248/using-ffmpeg-to-get-video-info-why-do-i-need-to-specify-an-output-file
## http://www.techanswerguy.com/2012/03/redirecting-ffmpeg-output-performing.html
## https://groups.google.com/forum/#!msg/nodejs/7KakLQR50_w/yEVW1-kA-boJ
## http://www.computerhope.com/forum/index.php?topic=110250.0
##########################################################################
## Started: 2014jun17 Based on a similar PROPERTIES script from the
##                    feNautilusScripts system at www.freedomenv.com.
##                    But that script uses temporary files and the
##                    'grep' and 'tail' commands instead of 'awk'.
## Changed: 2014
###########################################################################

## FOR TESTING: (show statements as they execute)
# set -x

#########################################
## Get the filename passed to this script.
#########################################

FILENAME="$1"

## FOR TESTING:
#  FILENAME="$HOME/TESTfilesMOVIES/mpeg/ParkingTechnique2_320x240_12sec_MPEG1-MP2.mpeg"

#########################################
## Pass a heading to stdout.
#########################################

echo "\
'ffmpeg -i' output:
##################
"

########################################################################
## Pass the output of 'ffmpeg -i "$FILENAME"' to a small awk' program
## that extracts the properties of the movie file.
########################################################################
## CAUTION: Single-quotes in comment lines of an awk script cause syntax
##          errors --- like braces in comment lines cause errors in
##          Tcl-Tk scripts.
##          Use double-quotes instead.
########################################################################

ffmpeg -i "$FILENAME" 2>&1 | awk '
BEGIN {
   KEEP=0;
   ## KEEP is a flag. It will be set to 1 when we encounter the "built on" rec.
}
{
   ################################################
   ## Hold the first 12 characters of this record,
   ## whose contents are in $0.
   ################################################

   FIELD1=substr($0,1,12)

   #########################################################################
   ## If KEEP=0 and this rec does not contain the string "built on", skip
   ## this rec (read the next one). We want to read to the "built on" rec.
   #########################################################################

   if ( FIELD1 !~ "built on" && KEEP==0) next

   #########################################################################
   ## If this rec contains the string "built on", set KEEP=1 and
   ## read the next rec.
   #########################################################################

   if ( FIELD1 ~ "built on" && KEEP==0) {
      KEEP=1
      next
   }

   #########################################################################
   ## If this rec contains the string "At least one" (as in
   ## "At least one output file must be specified"), exit.
   #########################################################################

   if ( FIELD1 ~ "At least one") {exit}

   #########################################################################
   ## If we get here, this is a record we want. Print it.
   #########################################################################

   print $0
}'
## END OF the awk script.