ffmpeg -f image2 -i wow%3d.png -vf fps -pix_fmt yuva420p -metadata:s:v:0  alpha_mode="1" output.webm



OUTPUT:

C:\Users\Thomas\Desktop\Tools\FFMPEG\bin>ffmpeg -f image2 -i wow%3d.png -vf fps
-pix_fmt yuva420p -metadata:s:v:0  alpha_mode="1" output.webm
ffmpeg version N-78335-g9ee4c89 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 5.3.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
ibilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enab
le-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --ena
ble-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --
enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-lib
x265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-d
ecklink --enable-zlib
  libavutil      55. 17.100 / 55. 17.100
  libavcodec     57. 24.101 / 57. 24.101
  libavformat    57. 24.101 / 57. 24.101
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 29.100 /  6. 29.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, image2, from 'wow%3d.png':
  Duration: 00:00:06.00, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: png, rgba(pc), 1280x720, 25 fps, 25 tbr, 25 tbn, 25 tbc
Incompatible pixel format 'yuva420p' for codec 'libvpx-vp9', auto-selecting form
at 'yuv420p'
[libvpx-vp9 @ 0000000000161c40] v1.5.0
Output #0, webm, to 'output.webm':
  Metadata:
    encoder         : Lavf57.24.101
    Stream #0:0: Video: vp9 (libvpx-vp9), yuv420p, 1280x720, q=-1--1, 200 kb/s,
25 fps, 1k tbn, 25 tbc
    Metadata:
      alpha_mode      : 1
      encoder         : Lavc57.24.101 libvpx-vp9
    Side data:
      unknown side data type 10 (24 bytes)
Stream mapping:
  Stream #0:0 -> #0:0 (png (native) -> vp9 (libvpx-vp9))
Press [q] to stop, [?] for help
frame=   36 fps=0.0 q=0.0 size=       1kB time=00:00:00.48 bitrate=  23.6kbits/s
frame=   48 fps= 44 q=0.0 size=       5kB time=00:00:00.96 bitrate=  40.6kbits/s
frame=   56 fps= 35 q=0.0 size=      11kB time=00:00:01.28 bitrate=  72.8kbits/s
frame=   63 fps= 30 q=0.0 size=      15kB time=00:00:01.56 bitrate=  81.2kbits/s
frame=   68 fps= 26 q=0.0 size=      22kB time=00:00:01.76 bitrate= 102.3kbits/s
frame=   75 fps= 24 q=0.0 size=      25kB time=00:00:02.04 bitrate= 101.3kbits/s
frame=   80 fps= 21 q=0.0 size=      34kB time=00:00:02.24 bitrate= 123.5kbits/s
frame=   86 fps= 19 q=0.0 size=      42kB time=00:00:02.48 bitrate= 139.2kbits/s
frame=   92 fps= 18 q=0.0 size=      45kB time=00:00:02.72 bitrate= 135.5kbits/s
frame=   97 fps= 18 q=0.0 size=      51kB time=00:00:02.92 bitrate= 142.7kbits/s
frame=  103 fps= 17 q=0.0 size=      54kB time=00:00:03.16 bitrate= 139.8kbits/s
frame=  107 fps= 16 q=0.0 size=      61kB time=00:00:03.32 bitrate= 151.5kbits/s
frame=  112 fps= 16 q=0.0 size=      64kB time=00:00:03.52 bitrate= 149.6kbits/s
frame=  118 fps= 15 q=0.0 size=      70kB time=00:00:03.76 bitrate= 151.7kbits/s
frame=  125 fps= 15 q=0.0 size=      72kB time=00:00:04.04 bitrate= 146.1kbits/s
frame=  130 fps= 15 q=0.0 size=      79kB time=00:00:04.24 bitrate= 153.0kbits/s
frame=  136 fps= 15 q=0.0 size=      83kB time=00:00:04.48 bitrate= 150.9kbits/s
frame=  144 fps= 15 q=0.0 size=      86kB time=00:00:04.80 bitrate= 146.7kbits/s
frame=  150 fps= 14 q=0.0 Lsize=      88kB time=00:00:06.00 bitrate= 119.7kbits/
s speed=0.554x
video:86kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing ov
erhead: 1.686851%