mux demux different sizes

[Guest]

Archived from groups: rec.video.desktop (More info?)

Hi. Boy this video stuff is complicated. I have a 790 MB video file. I
was advised to demux and mux it with tMPGenc. When I am done demux and
muxing it it is 590 MB. Why? I did it twice, made sure that the
product was svcd mpg2 vbr, though curiously if I do it as vcd mpg1 it
is almost the same size. And avicodec says that it is indeed mpg2. I
don't get it.

Thanks,

IMF

 

[martin]

Archived from groups: rec.video.desktop (More info?)

"Irwin Feuerstein" <ebct@hotmail.com> wrote in message
news:542d2ca5.0411081525.56dffe39@posting.google.com...
> Hi. Boy this video stuff is complicated. I have a 790 MB video file. I
> was advised to demux and mux it with tMPGenc. When I am done demux and
> muxing it it is 590 MB. Why? I did it twice, made sure that the
> product was svcd mpg2 vbr, though curiously if I do it as vcd mpg1 it
> is almost the same size. And avicodec says that it is indeed mpg2. I
> don't get it.
>
> Thanks,
>
> IMF

Maybe the original was padded.
The video stream can be padded with null data which brings the bitrate up to
a desired level.
A low bitrate video may be padded to ensure that the decoder receive enough
data to process/decode successfully.

When you encode VBR with TMPGEnc you'll see a setting in the MPEG Settings
under Rate Control Mode.
Here you can turn padding on or off when you encode a video.

So i'd guess that your original video had the stream padded with null data
so that it reached a minimum bitrate - and now that you've demuxed and
remuxed it, the video no longer has the extra padding.

Martin.