avconv version 9.16-6:9.16-0ubuntu0.14.04.1, Copyright (c) 2000-2014 the Libav developers
  built on Aug 10 2014 18:16:02 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
[image2pipe @ 0x7d6120] max_analyze_duration reached
[image2pipe @ 0x7d6120] Estimating duration from bitrate, this may be inaccurate
Input #0, image2pipe, from 'pipe:':
  Duration: N/A, bitrate: N/A
    Stream #0.0: Video: png, gray, 500x500, 25 fps, 25 tbr, 25 tbn
[libx264 @ 0x7e5cc0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[libx264 @ 0x7e5cc0] profile High, level 3.0
[libx264 @ 0x7e5cc0] 264 - core 142 r2389 956c8d8 - H.264/MPEG-4 AVC codec - Copyleft 2003-2014 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.25 aq=1:1.00
Output #0, mp4, to 'out.mp4':
  Metadata:
    encoder         : Lavf54.20.4
    Stream #0.0: Video: libx264, yuv420p, 500x500, q=-1--1, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png -> libx264)
Press ctrl-c to stop encoding
Error while decoding stream #0:0
    Last message repeated 480 times
pipe:: Input/output error
frame=    0 fps=  0 q=0.0 Lsize=       0kB time=10000000000.00 bitrate=   0.0kbits/s
video:0kB audio:0kB global headers:0kB muxing overhead 610.000000%