Bug 18221

These are the errors:

SWFDEC: ERROR: swfdec_video_decoder_gst.c(149): swfdec_video_decoder_gst_decode: failed to pull decoded buffer. Broken stream?
SWFDEC: ERROR: swfdec_net_stream.c(96): swfdec_net_stream_decode_video: can't reduce size by more than available

Looks the same has been reported here:
https://bugs.freedesktop.org/show_bug.cgi?id=14496#c3

"Accidentally, I found that certain flashvideo cannot start with swfdec. 
Sound is played, but seekbar and moviearea remain plain. When I save the .flv
to the disk, mplayer plays it correctly and the debug prints that it does so by
using ffmpeg's libavcodec codec family. Movie URL is at:
http://vbox7.com/play:d8169841"

> "Accidentally, I found that certain flashvideo cannot start with swfdec. 
> Sound is played, but seekbar and moviearea remain plain. When I save the .flv
> to the disk, mplayer plays it correctly and the debug prints that it does so by
> using ffmpeg's libavcodec codec family. Movie URL is at:
> http://vbox7.com/play:d8169841"
> 

I'm encountering the same problem, usually on YouTube:

Youtube videos don't play correctly. If I do nothing and just let the video play, the video usually stays at one fixed frame until I scroll around the page a bit. I have a pretty weak processor - 630 Mhz (standard downclocked Eee PC processor), but when I just download the FLV file and play it in Totem the video DOES play at full speed.

I wonder if I should file a seperate bug report because this thing has only been reported in comments, it seems... This bug persists for me in a freshly compiled 0.8.2.

> Youtube videos don't play correctly. If I do nothing and just let the video
> play, the video usually stays at one fixed frame until I scroll around the page
> a bit. I have a pretty weak processor - 630 Mhz (standard downclocked Eee PC
> processor)
>
This has to do with Swfdec skipping the rednering of frames when the CPU is fully loaded. Unfortunately, it might just skip _all_ frames, which results in the image never updating.
So the reason Swfdec does not play Youtube is that its script interpreter is too slow for your computer - or vice versa: your computer is too slow for Swfdec, your choice :)
Out of interest: Does Adobe's player work?

> when I just download the FLV file and play it in Totem the
> video DOES play at full speed.
>
See http://swfdec.freedesktop.org/wiki/FAQ for why this happens.
 
> I wonder if I should file a seperate bug report because this thing has only
> been reported in comments, it seems... This bug persists for me in a freshly
> compiled 0.8.2.
> 
I don't think filing "Swfdec's script interpreter is too slow" is a useful idea. It's very unlikely to go away very soon, unless people show up to spend time optimizing the script interpreter. I'm personally way more interested in reaching feature parity with Adobe's player than in being faster, so you're unlikely to see it becoming lots faster.