Re: [Vnc2swf-users] Shrinking a vnc2flv file

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

On Wed, Nov 04, 2009 at 07:41:18PM -0600, Josh Harding wrote:
>    I can also note that for
>    archiving large recordings, running gzip on a raw vnc log results in
>    incredibly small files (even compared to the .flv's).  Playback is a
>    bit less convenient as you'd have to uncompress and convert to flv
>    before viewing.

How did you capture the raw vnc log in a replayable form?

I had a look at the vnc traffic using

    tcpdump -i lo -n -s0 -w /tmp/lo.pcap

and at the same time monitored the size of the .flv file being created. I
pointed it at a completely static browser window, which didn't have focus so
there wasn't even a blinking cursor in it.

As expected, the pcap showed an initial flurry of traffic and then was
completely static. However the .flv was continuing to grow - I measured this
at 200KBytes every 30 seconds. In bits-per-second that's 55kbps for a
completely static screen.

If it's storing a marker every frame, and 12 frames per second, then
that's about 580 bytes per identical frame.

I then tried flvrec with -r 4, and it only grew at 72KB per 30 seconds. So
the overhead looks to be proportional to frame rate. I think the default
frame rate is 12 fps, although the documentation at
http://www.unixuser.org/~euske/python/vnc2flv/index.html#flvrec.py
says it defaults to 15.

Maybe the per-frame overhead is proscribed by the flv format and can't be
reduced? :-(

I then tried flvrec -K 150 (and no -r flag), and the growth was 147KB
instead of 200KB. So the key frames have some effect it seems.

Regards,

Brian.