[FFmpeg-user] multiple fade out slow down encoding about two to three times

[Tomáš Hnyk]

Hello,
I created initial captions with fade ins and outs like this:

ffmpeg -i in.mov \
-framerate 24 -loop 1 -i a/01.png \
-framerate 24 -loop 1 -i a/02.png \
-framerate 24 -loop 1 -i a/03.png \
-framerate 24 -loop 1 -i a/04.png \
-framerate 24 -loop 1 -i a/05.png \
-framerate 24 -loop 1 -i a/06.png \
-framerate 24 -loop 1 -i a/07.png \
-framerate 24 -loop 1 -i a/08.png \
-framerate 24 -loop 1 -i a/09.png \
-filter_complex \
"[1:v]fade=in:0:d=0.2,fade=out:20:d=0.2[fad1]; \
[2:v]fade=in:28:d=0.2,fade=out:48:d=0.2[fad2]; \
[3:v]fade=in:56:d=0.2,fade=out:76:d=0.2[fad3]; \
[4:v]fade=in:84:d=0.2,fade=out:104:d=0.2[fad4]; \
[5:v]fade=in:112:d=0.2,fade=out:132:d=0.2[fad5]; \
[6:v]fade=in:140:d=0.2,fade=out:160:d=0.2[fad6]; \
[7:v]fade=in:168:d=0.2,fade=out:188:d=0.2[fad7]; \
[8:v]fade=in:196:d=0.2,fade=out:216:d=0.2[fad8]; \
[9:v]fade=in:224:d=0.2,fade=out:265:d=0.2[fad9]; \
[0:v][fad1]overlay=0:0:enable='between(t,0,1)'[tmp1]; \
[tmp1][fad2]overlay=0:0:enable='between(t,1.2,2.2)'[tmp2]; \
[tmp2][fad3]overlay=0:0:enable='between(t,2.4,3.4)'[tmp3]; \
[tmp3][fad4]overlay=0:0:enable='between(t,3.6,4.6)'[tmp4]; \
[tmp4][fad5]overlay=0:0:enable='between(t,4.8,5.8)'[tmp5]; \
[tmp5][fad6]overlay=0:0:enable='between(t,6,  7  )'[tmp6]; \
[tmp6][fad7]overlay=0:0:enable='between(t,7.2,8.2)'[tmp7]; \
[tmp7][fad8]overlay=0:0:enable='between(t,8.4,9.4)'[tmp8]; \
[tmp8][fad9]overlay=0:0:enable='between(t,9.6,11.2)'[tmp9]; \
[tmp9]ass=../subtitles.ass[outv]" \
-map [outv] -map a:0 \
-c libx264 -preset slow  -profile:v high -crf 19 \
-strict -2 -c:a aac -b:a 192k \
-f mov -y out.mov

It encodes at 5.5 fps if I let it run for five minutes (the video is  
almost two hours)
If I instead do:

ffmpeg -i in.mov \
-i a/01.png -i a/02.png -i a/03.png -i a/04.png -i a/05.png -i a/06.png -i  
a/07.png -i a/08.png -i a/09.png \
-filter_complex \
"[0:v][1:v]overlay=0:0:enable='between(t,0,1)'[tmp1]; \
[tmp1][2:v]overlay=0:0:enable='between(t,1.2,2.2)'[tmp2]; \
[tmp2][3:v]overlay=0:0:enable='between(t,2.4,3.4)'[tmp3]; \
[tmp3][4:v]overlay=0:0:enable='between(t,3.6,4.6)'[tmp4]; \
[tmp4][5:v]overlay=0:0:enable='between(t,4.8,5.8)'[tmp5]; \
[tmp5][6:v]overlay=0:0:enable='between(t,6,  7  )'[tmp6]; \
[tmp6][7:v]overlay=0:0:enable='between(t,7.2,8.2)'[tmp7]; \
[tmp7][8:v]overlay=0:0:enable='between(t,8.4,9.4)'[tmp8]; \
[tmp8][9:v]overlay=0:0:enable='between(t,9.6,11.2)'[tmp9]; \
[tmp9]ass=../neposunute.ass[outv]" \
-map [outv] -map a:0 \
-c libx264 -preset slow  -profile:v high -crf 19 \
-strict -2 -c:a aac -b:a 192k \
-f mov -y  out.mov

It encodes in roughly 14 fps. But fade ins and outs occur only at the very  
beginning (in the first 11 seconds), yet the slow down is preserved (I  
also run the compilation for about five minuts). Is this a performance bug?
Regards,
Tomas