[Vnc2swf-users] Shrinking a vnc2flv file

[Brian C. <B.C...@po...>]

This isn't exactly a vnc2flv problem, but I thought this would be a
reasonable place to ask anyway.

I have used vnc2flv to create a screencast which is 9 mins 27 secs long, at
a screen size of 992 x 608. [The large screen area is because the app I'm
capturing really needs this much space]. The resulting file is 19.1MB.

Now, I would like to reduce the file size significantly. I am happy to
reduce the picture 2:1 so that it becomes 496 x 304. I can do this using
ffmpeg (*), and the picture quality is usable for my purpose:

    ffmpeg -i in.flv -s 496x304 -r 4 -acodec copy -y out.flv

However the resultant file is still 12MB in size, even after dropping the
output frame rate to 4fps!

I tried outputting using the 'flashsv' codec (**):

    ffmpeg -i in.flv -s 496x304 -vcodec flashsv -r 4 -acodec copy -y out-flashsv.flv

but now the resultant file is even larger, at 16.2MB.

LAME tells me it's encoding the audio at 32kbps mono, in which case that
only accounts for about 2.2MB of the total.

Here's what 'ffplay -stats' says about the source file (19MB):

Input #0, flv, from 'in.flv': 0KB vq=    0KB sq=    0B    
  Duration: 00:09:26.66, start: 0.000000, bitrate: 32 kb/s
    Stream #0.0: Video: flashsv, bgr24, 992x608, 12 tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: mp3, 22050 Hz, mono, s16, 32 kb/s
  23.81 A-V:  4.297 aq=   79KB vq=  498KB sq=    0B 

and the version shrunk as 'flv' (12MB):

Input #0, flv, from 'out.flv': vq=    0KB sq=    0B    
  Duration: 00:09:27.00, start: 0.000000, bitrate: 232 kb/s
    Stream #0.0: Video: flv, yuv420p, 496x304, 200 kb/s, 4 tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: mp3, 22050 Hz, mono, s16, 32 kb/s
  23.49 A-V: -0.027 aq=   79KB vq=  170KB sq=    0B    

and the version shrunk as 'flashsv' (16MB):

Input #0, flv, from 'out-flashsv.flv':
  Duration: 00:09:27.00, start: 1257374691.83 A-V:  0.000 aq=    0KB vq=    0KB 0.000000, bitrate: 232 kb/s
    Stream #0.0: Video: flashsv, bgr24, 496x304, 200 kb/s, 4 tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: mp3, 22050 Hz, mono, s16, 32 kb/s
  23.00 A-V: -0.015 aq=   80KB vq=  232KB sq=    0B    

So, do you have any suggestions about how I could improve this? Have I
missed an important option from ffmpeg? Is there a better way to shrink a
vnc2flv stream?

Many thanks,

Brian.

(*) ffmpeg is the stock version from Ubuntu Jaunty:

ii  ffmpeg                                     3:0.svn20090303-1ubuntu6                         multimedia player, server and encoder
ii  gstreamer0.10-ffmpeg                       0.10.6.2-1ubuntu2                                FFmpeg plugin for GStreamer
ii  libavcodec-unstripped-52                   3:0.svn20090303-1ubuntu2+unstripped1             ffmpeg codec library
ii  libavdevice52                              3:0.svn20090303-1ubuntu6                         ffmpeg device handling library
ii  libavfilter0                               3:0.svn20090303-1ubuntu6                         ffmpeg video filtering library
ii  libavformat52                              3:0.svn20090303-1ubuntu6                         ffmpeg file format library
ii  libavutil-unstripped-49                    3:0.svn20090303-1ubuntu2+unstripped1             ffmpeg utility library
ii  libpostproc51                              3:0.svn20090303-1ubuntu6                         ffmpeg video postprocessing library
ii  libswscale0                                3:0.svn20090303-1ubuntu6                         ffmpeg video scaling library

(**) According to Wikipedia, flash video supports two tiling codecs
specifically for screencasts, so I guess that 'flashsv' is one of those. I
also saw a recent posting to this list showing '-vcodec flashsv'.