[vlc-devel] Re: forcing PES alignment to 188 bytes

Måns Rullgård mru at inprovide.com
Fri Jun 30 19:02:15 CEST 2006

Greg Farrell <greg at gregfarrell.org> writes:

> Hi,
> I'm trying to use vlc generated transport streams which contain mpgv
> video and mpga audio with a Kasenna server. The Kasenna refuses to
> import them with an error of "*Error* asset has a bit-rate less than
> 64 kbps"
> According to google and Trax in #videolan this error is because my
> mpeg content doesn't have a PES packet size a multiple of 188. So zero
> length adaption fields are confusing the Kasenna.

That utterly nonsensical error is reported by Kasenna if the transport
stream has any bitrate variance whatsoever.  Bitrate in this case is
determined by the PCR.  As long as you keep the mux rate constant,
padding with null packets as needed, the Kasenna server will accept
just about anything at the PES level.  I believe this requirement is
so they can simply pump out the file at a constant rate without
looking at the timestamps.

Getting the bitrate right is only the first hurdle when dealing with a
Kasenna server.  The next problem you're likely to face is trickplay.
When a video is loaded, the Kasenna server extracts the I frames (and
maybe some P frames if B frames are used), and uses these to construct
fast forward and rewind streams in separate files.  A set of indexes
are used to map file offsets in the main stream to the corresponding
locations in the trickplay streams and back.  The problem is that this
index is often off by large amounts, sometimes minutes.  This leads to
some annoying effects when switching between normal play and
trickplay, e.g. activating fast forward jumps 5 minutes ahead and
starts playing at FF speed, and going back to normal speed does a
similar 5-minute jump backward.  I never managed to figure out what
was the cause of this quirk.

If you are not already tied up with those servers, take my advice and
use something else.  Kasenna systems are a world of pain.

Måns Rullgård
mru at inprovide.com

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