[FFmpeg-user] Wrong FPS while screencasting.

[dE .]

Now, when I screencast, I always see 30 FPS in the output, but the 
recorded videos are definitely not at 30 FPS.

This's reproducible every codec.

fmpeg -f x11grab -s 1280x800 -i :0.0 -threads 4 -x264opts qp=0 -preset 
ultrafast -vcodec libx264 test.mp4
ffmpeg version N-37922-g28ba102 Copyright (c) 2000-2012 the FFmpeg 
developers
   built on Feb 16 2012 09:48:31 with gcc 4.5.3
   configuration: --prefix=/usr --libdir=/usr/lib64 
--shlibdir=/usr/lib64 --mandir=/usr/share/man --enable-shared 
--cc=x86_64-pc-linux-gnu-gcc --cxx=x86_64-pc-linux-gnu-g++ 
--ar=x86_64-pc-linux-gnu-ar --optflags='-march=native -O2 
-fomit-frame-pointer -floop-interchange -floop-strip-mine -floop-block 
-fgraphite-identity' --extra-cflags='-march=native -O2 
-fomit-frame-pointer -floop-interchange -floop-strip-mine -floop-block 
-fgraphite-identity' --extra-cxxflags='-march=native -O2 
-fomit-frame-pointer -floop-interchange -floop-strip-mine -floop-block 
-fgraphite-identity' --disable-static --enable-gpl --enable-version3 
--enable-postproc --enable-avfilter --disable-stripping --disable-debug 
--disable-doc --disable-network --disable-vaapi --disable-vdpau 
--enable-libmp3lame --enable-libvo-aacenc --enable-libvo-amrwbenc 
--enable-libtheora --enable-libvorbis --enable-libx264 --enable-libxvid 
--enable-libaacplus --enable-nonfree --enable-openal --disable-indev=v4l 
--disable-indev=v4l2 --disable-indev=oss --disable-i  libavutil      51. 
39.100 / 51. 39.100
   libavcodec     54.  3.100 / 54.  3.100
   libavformat    54.  1.100 / 54.  1.100
   libavdevice    53.  4.100 / 53.  4.100
   libavfilter     2. 62.100 /  2. 62.100
   libswscale      2.  1.100 /  2.  1.100
   libswresample   0.  6.100 /  0.  6.100
   libpostproc    52.  0.100 / 52.  0.100
[x11grab @ 0x1039090] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 
1280 height: 800
[x11grab @ 0x1039090] shared memory extension found
[x11grab @ 0x1039090] Estimating duration from bitrate, this may be 
inaccurate
Input #0, x11grab, from ':0.0':
   Duration: N/A, start: 1329391769.095059, bitrate: 982057 kb/s
     Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1280x800, 
982057 kb/s, 29.97 tbr, 1000k tbn, 29.97 tbc
File 'test.mp4' already exists. Overwrite ? [y/N] y
Incompatible pixel format 'bgr0' for codec 'libx264', auto-selecting 
format 'yuv420p'
[buffer @ 0x1045fb0] w:1280 h:800 pixfmt:bgr0 tb:1/1000000 sar:0/1 
sws_param:
[buffersink @ 0x1048920] auto-inserting filter 'auto-inserted scale 0' 
between the filter 'src' and the filter 'out'
[scale @ 0x1048c90] w:1280 h:800 fmt:bgr0 -> w:1280 h:800 fmt:yuv420p 
flags:0x4
[libx264 @ 0x1047620] using cpu capabilities: MMX2 SSE2Slow SlowCTZ
[libx264 @ 0x1047620] profile High 4:4:4 Predictive, level 3.2, 4:2:0 8-bit
[libx264 @ 0x1047620] 64 - core 118 - H.264/MPEG-4 AVC codec - Copyleft 
2003-2011 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 
deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=0 mixed_ref=0 me_range=16 
chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=0 
chroma_qp_offset=0 threads=4 sliced_threads=0 nr=0 decimate=1 
interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 
keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=cqp mbtree=0 qp=0
Output #0, mp4, to 'test.mp4':
   Metadata:
     encoder         : Lavf54.1.100
     Stream #0:0: Video: h264 (![0][0][0] / 0x0021), yuv420p, 1280x800, 
q=-1--1, 30k tbn, 29.97 tbc
Stream mapping:
   Stream #0:0 -> #0:0 (rawvideo -> libx264)
Press [q] to stop, [?] for help
frame=  408 fps= 32 q=-1.0 Lsize=    2529kB time=00:00:13.61 
bitrate=1522.0kbits/s dup=245 drop=0
video:2527kB audio:0kB global headers:0kB muxing overhead 0.094609%
[libx264 @ 0x1047620] frame I:2     Avg QP: 0.00  size:197778
[libx264 @ 0x1047620] frame P:406   Avg QP: 0.00  size:  5398
[libx264 @ 0x1047620] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0x1047620] mb P  I16..4: 48.6%  0.0%  0.0%  P16..4:  0.1%  
0.0%  0.0%  0.0%  0.0%    skip:51.3%
[libx264 @ 0x1047620] coded y,uvDC,uvAC intra: 1.6% 0.9% 0.9% inter: 
0.1% 0.2% 0.2%
[libx264 @ 0x1047620] i16 v,h,dc,p: 98%  2%  0%  0%
[libx264 @ 0x1047620] i8c dc,h,v,p: 96%  2%  1%  0%
[libx264 @ 0x1047620] kb/s:1520.23