[mythtv-users] Why do those mpeg files not play? (capture with a ceton infiniTV 4)

[Jay Ashworth]

----- Original Message -----
> From: "Ronald Frazier" <ron at ronfrazier.net>

> I know a little bit of very basic info about MPEG packets, PAT/PMT
> packets, PIDs, etc, but I don't know a whole lot about what to expect
> in a valid mpeg stream, but I'm starting to learn a bit more about it.
> I found a nice program called the MPEG-2 TS packet analyser 2.3.0.0,
> and it's pretty handy.
> 
> I'm looking at some of the files generated by the ceton, and comparing
> them to files generated by the hd homerun (using hdhomerun_config to
> tune and save the file). I'm noticing a few differences, which I think
> may be key:

The thing to understand here, that's most important, is that the HDHR 
doesn't *generate* anything: it's a modem.  It takes the MPEG transport
streams that come OTA or OTC, and hands them to you, AFAIK, raw.

So you're at the mercy of what ever generated the program streams, and 
whatever multiplexed them into a transport stream.
 
> PID 0 packets (PAT) - these packets contain info about all of the
> programs (ie: virtual sub-channels or multiplexes) that are contained
> in the tuned QAM channel. If the cable company has 10 programs packed
> into, there will be 10 entries in this packet, listing the PID number
> of each program. The HDHR seems to rewrite these packets to filter it
> down to just 1 entry (the program you tuned) regardless of how many
> programs the cable company broadcasts. The Ceton, on the other hand,
> passes you the raw packets with all of the programs listed.

Interesting.

Modify my above assertion accordingly.  :-)

> So my questions are, for someone more familiar with the MPEG spec (or
> if anyone know which of the myth developers would be the best one to
> ask):
> 1) Does my explanation sound about right (maybe not perfect, but at
> least have I got the general idea), and

I'd say, without looking at the files myself, that you're pretty close.

> 2) Is what the ceton is doing...is that considered to be valid data,
> or should it be filtering those extra packets? If anyone is lucky
> enough to have worked with or have sample files from a pre-release
> HDHR Prime, does it do the same sort of thing, or does it filter more
> strictly like the regular HDHR does? I'm wondering if this is a bug
> Ceton should be fixing, or if software is just supposed to know how to
> deal with it (and most of them just don't do a good job with
> tolerating it)?

Well, this is all a matter of taste, and it depends a lot on what the device
expects it's attached client to *do* -- and how much bandwidth you have.

My personal taste would be to not filter anything -- and I suspect multirec
both requires, and gets, this -- you didn't say if you have multirec
running on the box that captured those files or not... but as I say,
depends on what your software requires.

Cheers,
-- jra
-- 
Jay R. Ashworth                  Baylink                       jra at baylink.com
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