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List:       mjpeg-users
Subject:    Re: [Mjpeg-users] mpeg2enc's bitrate parameter does not work
From:       mjpeg-users () thoth ! purplefrog ! com
Date:       2009-04-08 18:31:44
Message-ID: 20090408143144.204cc962.thoth () purplefrog ! com
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In 49D839D5.6020607@utanet.at, Bernhard Praschinger <shadowlord@utanet.at> wrote:

> So you try to rencode the video.
> Can you please post the mpeg format, resolution and aspect ration the 
> source has. And the output format you want.

  The source video was 512x480, 29.97 Hz.  4:3 aspect ratio (captured
from TV using a Hauppage card).  It was what I think would be called an
MPEG system stream.  By the time I dropped it into the YUV file it had
been converted to 352x480.

  I am trying to create an MPEG transport stream that compiles with the
Cable Labs VOD 1.1 encoding spec.  Unfortunately all I could find on-line is the
2.0 spec at
http://www.cablelabs.com/specifications/MD-SP-VOD-CEP2.0-I02-070105.pdf
which does not have identical limitations on the video rate.

Roughly speaking I need IBBP video, <=3.18MBit/s, 15 frame GOPs,
sequence header per GOP.  The stuff that comes from commercial hardware
encoders also includes sequence_extension and picture_coding_extension
packets, but I do not think those are actually required.

mpeg2enc is just a small piece of the equation.  There are no free
software tools that can create an MPEG transport stream that isn't utter
garbage (and finding a commercial one that works well enough for VOD is
something of a chore too).

> 
> > mpeg2enc -a 2 -b 3180 -g 15 -G 15 -s -R 2  \
> > /homes4/thoth/drinky-crow/x.yuv \
> > -o /homes4/thoth/drinky-crow/x.m2v
> I hope you know that you generate a fixed bitrate MPEG1 with a aspect 
> ratio of 4:3 and a fixed gop size.

  That's what I asked it to do, but it did not perform as advertised
(with respect to the bit rate).

> Can you try to encode without the -R 2 option and see what happens.
> I haven't encoded a MPEG1 with that kind of parameters for a long time.

  That gives me an IP* stream which does not comply with section 4.8 of
MD-SP-VOD-CEP-I01-040107 (CabLabs Video-On-Demand Content Encoding
Profiles Specification).  More importantly, the bit rate is still way
wrong. Based on the file size I think it's doing around 9Mbit/s.

  The aspect_ratio_information is also still wrong (12 instead of 2). 

> > Both files play in mplayer, but the .m2v doesn't have the correct aspect
> > ratio (-a 2 isn't being honored, and the
> > sequence_header.aspect_ratio_information contains a 12 instead).
...
> Does the yuv file look correct when you play it back with lavplay (cat 
> x.yuv | yuvplay) ?

  It plays as well with yuvplay as it did with mplayer.  It looks fine.

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