[ExtractStream] Possible end of ZSS development...

[Edmond E. Shwayri]

One other piece of anecdotal info we can derive from where PES packets are 
placed. If you look you will see a common :

PES I1 PES B1 PES B2 P1 PES B3 PES B4 P2

This makes sense because the order I think things are done in is :

[1] Encode I Frame and give to TiVo stream creator.
[2] Hold Frame 2.
[3] Hold Frame 3.
[4] Encode Frame 4.
[5] Encode frame 2 based on I (Frame 1) and P (Frame 4) and transmit to 
TiVo stream creator.
[6] Encode frame 3 based on I (Frame 1) and P (Frame 4). Frame 4 is 
already encoded so pass both along to the TiVo stream creator.

The fact that the second B and the following P get spit out at the same 
time makes a lot of sense if the P was used to derive the B. I think the 
TiVo is storing the frames in the presentation order.

At 02:06 AM 4/18/02, you wrote:
>Hi,
>
>Just reading your mail, and I noticed a point in which you mention
>re-ordering the IPB frames. Why on earth do you want to do this? They are
>in the correct order already (from what I have gathered).
>If you are making this assumption based on the fact that the first GOP of a
>standard mpeg produced stream runs
>
>IPBBPBBPBBPBBPBBPBBIBBPBBPBBPBBPBBP
>
> ^
> notice here - do you see that the sequence gets into a
>familiar pattern?
>
>and you assume that Tivo is
>
>IBBPBBPBBPBBPBBP....
>
>so must need re-ordering then this is not correct.
>
>The MPEG2 specification says that B frames are reconstructed against the
>previous and next I or P frame. In the case of the Tivo stream, if you
>number the frames the actual order would be
>
>1xx423756....
>
>Without looking into it at some great length I couldn't say 100% that this
>is correct in the case of the Tivo, but as a standard Tivo stream decodes on
>a reference MPEG2 decoder (without errors) then I can say with some
>certainty that the stream is a valid ES.
>
>Jim
>
>-----Original Message-----
>From: Roger Merchberger [mailto:zmerch7@y...]
>Sent: 18 April 2002 01:12
>To: ExtractStream@yahoogroups.com
>Subject: [ExtractStream] Possible end of ZSS development...
>
>
>Holymygoodness! Don't let that scare you... I'm not leaving the
>scene or moving to Antarctica or anything, but I think I've finally
>gone beyond the "know just enough to be dangerous" stage & am ready
>to totally redefine the structure of the splitstream/zss code.
>
>I've been making changes to zss 0.56 (no, it's a hack so it's not on
>the webpage) to get it to figure out the GOP frame timestamps and I
>think I've [eek] succeeded [first time I've diddled with bitshifting
>in C!] -- except -- with Edmond's help, I've figured out that the
>MPEG video frame breaks & the Tivo video frame breaks are nowhere
>near a 1:1 ratio - including [but not limited to] the GOP headers.
>:-(
>
>Splitstream (and of course zss) is set up to: 1) slurp in a chunk 2)
>spit out A & V 3) throw away the rest, 4) rinse & repeat. Getting the
>Video to split on GOP headers, the possible reorganizing of I, P & B
>frames to a different order (if necessary) and other things would be
>just too hard to try to hack into the existing code as it sits... not
>to mention a *lot* of the error messages that Joe had in splitstream
>seem to be never used, or only come out when the stream's fubar'd so
>bad that there's no point to continuing...
>
>So I'm thinking of stripping zss right down to it's skivvies &
>[mostly] starting from scratch. This will slow down development a
>little bit, as it will take some time to get a new code base in
>place, but it will enable us all to learn more about the streams, and
>hopefully get closer sooner to a fully self-synchronizing MPEG
>splitter.
>
>I may have to 're-add' a little bit of the chunk-handling code, but
>it seems like some of it is throwing out the baby with the bathwater;
>so we'll see.
>
>I have made a few more changes 'splainin' this on my webpage, and I
>started a Glossary: section - The usual questions, suggestions,
>whatever just email me & I'll do my best to get it in. For those
>folks just tuning in:
>
><http://www.30below.com/~zmerch/tivo/index.cfm>http://www.30below.com/~zmerch/tivo/index.cfm
>
>Hard to believe that I've gotten over 2150 hits to the page in under
>3 months!
>
>Laterz,
>Roger "Merch" Merchberger
>
>
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