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List:       linux-video
Subject:    Notes on how to make MPEGS
From:       Christoph Doerbeck A242369 <cdoerbec () cso ! fmr ! com>
Date:       1999-04-23 16:59:04


Greetings,

I have been playing with xawtv, vstream, and mpeg2encode (with vstream patches)
and have successfully been creating little MPEG clips (15-60 seconds, no 
audio).

Now I would like to add audio, and have had little luck finding any
references to how it's done?

I'm running RedHat 5.2 Linux, Kernel 2.0.36, with a WinTV404/NTSC.

Any info and/or suggestions would be greatly appreciated.  Links/addresses
to utilities would also be greatly honored.

- Christoph



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List:       linux-video
Subject:    Re: Notes on how to make MPEGS
From:       ME <Michael.Esser () gmx ! de>
Date:       1999-04-24 9:09:05

Christoph Doerbeck A242369 wrote:

> Greetings,
>
> I have been playing with xawtv, vstream, and mpeg2encode (with vstream patches)
> and have successfully been creating little MPEG clips (15-60 seconds, no
> audio).
>
> Now I would like to add audio, and have had little luck finding any
> references to how it's done?
>
>

You have to melt the mpeg video stream with the mpeg audio stream to a so called
'mpeg system stream'. An overview of utilities and documentation is at
www.mpeg.org (look at system streams). For Linux, there exists the mplex-utility.

But first of all, it's necessary to create a mpeg audio stream, for example with
the 'encode' tool of the 'MPEG Audio Subgroup Software Simulation Group' (look
again at mpeg.org).

(I realized, that 'mplex' has problems on working with MPEG 1 Layer 3 audio
streams. Any Idea ?)

I also use VStream  myself and would be glad to know which framerate at wich
resolution you achieve ? I always get poor perfomance.


cu




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List:       linux-video
Subject:    Re: Notes on how to make MPEGS
From:       Nathan <laredo () gnu ! org>
Date:       1999-04-24 15:07:16

> You have to melt the mpeg video stream with the mpeg audio stream to a so called
> 'mpeg system stream'. An overview of utilities and documentation is at
> www.mpeg.org (look at system streams). For Linux, there exists the mplex-utility.

Ok first, if you're doing mpeg2 encoding, you want to do a program stream
and not a system stream.  System streams are used for MPEG1.  Also, mpeg1
streams can be encoded in real time with audio and video with most of today's
current cpus.   You need to remember to use audio layer 2, not 3 for MPEG.

Second, if you want to allow playback on a hardware MPEG2 decoder, you need
to NOT use layer3 audio.  The standard studios use for MPEG2 encoding is 
layer 2 audio.  Only people passing around cd tracks use layer 3.   Third,
the audio needs to be in PES packets as does the video.

I am in the midst of a rewrite of mpeg2encode and mpeg2decode to support
both audio and video.   One thing you need to realize also is that the 
audio and video streams MUST be phase locked to each other.  This is not
an option but a requirement of the standard.  Any output you create with
sound card sampling and bt848 input will likely not be trivial to lip-sync.

> I also use VStream  myself and would be glad to know which framerate at wich
> resolution you achieve ? I always get poor perfomance.

This depends on your drive speed, unfortunately.  If you want good
quality clips, go out and buy 1024MB ram and create a large ram drive to
write to.  Of course you'll be limited to whatever will fit into your
ram drive (which will be short), but it will be perfect quality.

I'm working on a solution that will do real time encoding of VideoCD
(MPEG1 at roughly 1.4Mbps total bitrate) on a Pentium II, and real time 
encoding of MPEG2 audio (at 192kbps, layer 2), and video (at 6Mbps) on a
PIII.  I hope to have it ready within the next three months.

I hope to do the same on an Alpha and PowerPC once i get one of each.

A company I'm working with is also making a real-time 50Mbps 4:2:2 MPEG-2
encoder which will be supported under linux.  The price should be ~$10k.
I already have their MPEG-2 hardware decoder (4:2:2 50Mbps) supported
under linux -- it runs about $1500, unfortunately for most users here.
It was designed for the professional market with SDI, AES/EBU outputs,
genlock input, etc...   It does use the Video4Linux API and I hope to
get it into the next 2.2.x kernel.

-- Nathan Laredo
laredo@gnu.org


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