[patch] FFmpeg consuming bytes on stdin

[tamentis]

Hi,

I was debugging one of my friends' script which creates thumbnails for images and videos in a folder. The script does something like that:

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find target/folder | while read filename; do
    convert $filename[0] output.png
done

And he noticed that whenever a video is converted, the next image to be converted would always fail and the path would always lose its first character. Here is a small test case that reproduces this bug (assuming you have a video.mov file in the current directory):

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echo "foobar" | sh -c 'convert video.mov[0] out.png; cat'
oobar

It appears that something in convert is consuming a single byte on stdin when converting videos. After a little bit of digging I figured out that ffmpeg was doing it, here another test case using the same command template used in ImageMagick:

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echo "foobar" | sh -c "ffmpeg -v -1 -i video.mov -vframes 1 -vcodec pam -an -f rawvideo -y wat; cat"
oobar

It looks like ffmpeg is interactive by default and reads for user input unless called with the -nostdin parameter. The following suggested patch against svn trunk fixes that issue:

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Index: MagickCore/delegate.c
===================================================================
--- MagickCore/delegate.c       (revision 18525)
+++ MagickCore/delegate.c       (working copy)
@@ -99,8 +99,8 @@
     "  <delegate decode=\"https\" command=\""wget" -q -O "%o" "https:%M"\"/>"
     "  <delegate decode=\"ilbm\" command=\""ilbmtoppm" "%i" > "%o"\"/>"
     "  <delegate decode=\"man\" command=\""groff" -man -Tps "%i" > "%o"\"/>"
-    "  <delegate decode=\"mpeg:decode\" stealth=\"True\" command=\""ffmpeg" -v -1 -vframes %S -i "%i" -vcodec pam -an -f rawvideo -y "%u.pam" 2> "%Z"\"/>"
-    "  <delegate decode=\"null\" encode=\"mpeg:encode\" stealth=\"True\" command=\""ffmpeg" -v -1 -mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 300 -i "%M%%d.jpg" "%u.%m" 2> "%Z"\"/>"
+    "  <delegate decode=\"mpeg:decode\" stealth=\"True\" command=\""ffmpeg" -nostdin -v -1 -vframes %S -i "%i" -vcodec pam -an -f rawvideo -y "%u.pam" 2> "%Z"\"/>"
+    "  <delegate decode=\"null\" encode=\"mpeg:encode\" stealth=\"True\" command=\""ffmpeg" -nostdin -v -1 -mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 300 -i "%M%%d.jpg" "%u.%m" 2> "%Z"\"/>"
     "  <delegate decode=\"pcl:color\" stealth=\"True\" command=\""pcl6" -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=ppmraw" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "%s"\"/>
"    
     "  <delegate decode=\"pcl:cmyk\" stealth=\"True\" command=\""pcl6" -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=bmpsep8" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "%s"\"/>"
     "  <delegate decode=\"pcl:mono\" stealth=\"True\" command=\""pcl6" -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 -dAlignToPixels=0 -dGridFitTT=2 "-sDEVICE=pbmraw" -dTextAlphaBits=%u -dGraphicsAlphaBits=%u "-r%s" %s "-sOutputFile=%s" "%s"\"/>"

Suggestions? Thoughts?