Compressing videos recorded on a DVD recorder in Linux

I generally use avidemux to edit a video, but I'm not happy with the
quality of the compression that it does. I've tried both the fixed and
variable bitrate compression options.

I would like to use ffmpeg, but it's very complicated and my experiments
with it have been disappointing. (I don't really understand all the
bitrate stuff in the man page, which seems to have been written for
experts only.)

Can ffmpeg even do the job? If so, what options would I need on the
command line to compress a 42 minute mpg down to about 38 minutes?

Are there any other programs that can compress an mpg without ruining the
quality?

Thanks!

Rick

"Rick" <rick@nospamplease.org> wrote in message
news:00a57145$0$6607$c3e8da3@news.astraweb.com...
>I generally use avidemux to edit a video, but I'm not happy with the
> quality of the compression that it does. I've tried both the fixed and
> variable bitrate compression options.
>
> I would like to use ffmpeg, but it's very complicated and my experiments
> with it have been disappointing. (I don't really understand all the
> bitrate stuff in the man page, which seems to have been written for
> experts only.)
>
> Can ffmpeg even do the job? If so, what options would I need on the
> command line to compress a 42 minute mpg down to about 38 minutes?
>
> Are there any other programs that can compress an mpg without ruining the
> quality?
>
> Thanks!
>
> Rick
>

You want to "compress a 42 minute mpg down to about
38 minutes".

Just so you know, that makes no sense in the context of
your post. When speaking of compressing video, we are
not talking about changing its playing time.

(There are some special editing /processing techniques
that can be used to modify video and/or audio so that it can
be played back at a faster rate, with less distortion; but that
is not what is normally meant by "Compression" in the
situation you describe.)

If you are intent on re-compressing or further compressing
the assumed SD DVD compliant MPEG2 video that was
created by your DVD recorder, you have a number of options.

One would be to keep it as DVD compliant MPEG2 but use
a lower bit rate, to create a smaller (compressed) file. This
will entail some loss of quality. With a quality encoding program
and multi-pass VBR encoding process it need not be noticable,
for a reasonable amount of reduction in file size.

Another option is to use a more efficient compression
algorithm. There are MPEG4 compression formats such as
the ASP DivX/XviD and H.264, but I prefer the AVC/H.264
formats myself.

There are Linux video encoding programs, like MEcoder
that use the ffmpeg libraries.

You can also check out the guides at www.videohelp.com
www.doom9.org www.afterdawn.com

Luck;
Ken

On Sat, 31 Oct 2009 09:41:35 -0700, Rick wrote:

> I generally use avidemux to edit a video, but I'm not happy with the
> quality of the compression that it does. I've tried both the fixed and
> variable bitrate compression options.
>
> I would like to use ffmpeg, but it's very complicated and my experiments
> with it have been disappointing. (I don't really understand all the
> bitrate stuff in the man page, which seems to have been written for
> experts only.)
>
> Can ffmpeg even do the job? If so, what options would I need on the
> command line to compress a 42 minute mpg down to about 38 minutes?

You want to make the file size smaller by about 10% (I think ????)

Try in avidemux

open the source file

set the video format to MPEG-2 requant
in the configure option set the shrink factor to 1.1

set Audio to copy

set Format to MPEG-TS(A+V)

save to a new file.

>
> Are there any other programs that can compress an mpg without ruining
> the quality?
>

Requant only copies rather than re-encoding but if you try and reduce the
size too much then the video can become jerky.

Other applications? The only one I use is DTC (discrete cosine
transform) in DVDlab and they recommend no lower than 70% for the target
size.


--
rich

rich wrote:
> On Sat, 31 Oct 2009 09:41:35 -0700, Rick wrote:
>
>> I generally use avidemux to edit a video, but I'm not happy with the
>> quality of the compression that it does. I've tried both the fixed and
>> variable bitrate compression options.
>>
>> I would like to use ffmpeg, but it's very complicated and my experiments
>> with it have been disappointing. (I don't really understand all the
>> bitrate stuff in the man page, which seems to have been written for
>> experts only.)
>>
>> Can ffmpeg even do the job? If so, what options would I need on the
>> command line to compress a 42 minute mpg down to about 38 minutes?
>
> You want to make the file size smaller by about 10% (I think ????)
>
> Try in avidemux
>
> open the source file
>
> set the video format to MPEG-2 requant
> in the configure option set the shrink factor to 1.1
>
> set Audio to copy
>
> set Format to MPEG-TS(A+V)
>
> save to a new file.
>
>> Are there any other programs that can compress an mpg without ruining
>> the quality?
>>
>
> Requant only copies rather than re-encoding but if you try and reduce the
> size too much then the video can become jerky.

I don't understand how a program would reduce size without re-encoding.
I suppose it could drop frames.

Dave S.

On Sat, 31 Oct 2009 14:08:17 -0500, Dave S wrote:

> rich wrote:
>> On Sat, 31 Oct 2009 09:41:35 -0700, Rick wrote:
>>
>>> I generally use avidemux to edit a video, but I'm not happy with the
>>> quality of the compression that it does. I've tried both the fixed
>>> and variable bitrate compression options.
<snip>
>>>
>> Requant only copies rather than re-encoding but if you try and reduce
>> the size too much then the video can become jerky.
>
> I don't understand how a program would reduce size without re-encoding.
> I suppose it could drop frames.
>
> Dave S.

If you want more information, dust off your Phd. in physics and do a
search for "compression-domain requantization". Lots of references to
learned papers, patents.

A more understandable explanation is here

http://forum.doom9.org/showthread.php?t=63587

Old, but at least readable, especially the section about half way down
the page, starting
<quote>
Requantizing
The DVD Shrink transcode engine works by requantizing video data.
<un-q>
I've made a couple of screen shots, using a bitrate viewer, which shows
the difference between video straight from a DVD recorder before and
after using Avidemux.
The third shot is re-capturing the video with a capture card. It shows
the difference between the codec used by recorders, almost constant
bitrate, obviously set up to get 2 hrs standard quality on a DVD5 and the
ATI codec which definitely is variable bitrate and is a bit more
efficient.

http://www.imageno.com/67ihjgytvjhepic.html

The only problems I can foresee the OP having is maybe audio sync. Really
the file should be demuxed first, the video compressed and then remuxed
with the audio. Its try and see what works.

Of course the OP was a bit scrambled so all this might be a waste of time
LOL.



--
rich

On Sat, 31 Oct 2009 11:53:57 -0500, "Ken Maltby" <kmaltby@sbcglobal.net>
wrote:

>
> "Rick" <rick@nospamplease.org> wrote in message
> news:00a57145$0$6607$c3e8da3@news.astraweb.com...
>>I generally use avidemux to edit a video, but I'm not happy with the
>> quality of the compression that it does. I've tried both the fixed and
>> variable bitrate compression options.
>>
>> I would like to use ffmpeg, but it's very complicated and my experiments
>> with it have been disappointing. (I don't really understand all the
>> bitrate stuff in the man page, which seems to have been written for
>> experts only.)
>>
>> Can ffmpeg even do the job? If so, what options would I need on the
>> command line to compress a 42 minute mpg down to about 38 minutes?
>>
>> Are there any other programs that can compress an mpg without ruining
>> the quality?
>>
>> Thanks!
>>
>> Rick
>>
>>
> You want to "compress a 42 minute mpg down to about
> 38 minutes".
>
> Just so you know, that makes no sense in the context of
> your post. When speaking of compressing video, we are not talking about
> changing its playing time.
>
> Luck;
> Ken

You're right. I stated my case incorrectly.

I want to reduce the file size by about 10% without changing the playback
time.

>
> One would be to keep it as DVD compliant MPEG2 but use
> a lower bit rate, to create a smaller (compressed) file. This will
> entail some loss of quality.
>

This is what I've been trying to do, first with avidemux and then with
ffmpeg, but the results have been disappointing.

My problem with ffmpeg is that I don't think I'm using it correctly. I
first use it to determine the current bitrate, and then invoke it with a
lower bitrate, trying several times if needed until the final file size is
correct. But when I do it this way, the resulting quality is much lower.
Am I doing is right?

Maybe what I want is simply not possible.

In any case, many thanks to everyone that responded.


Rick

On Sat, 31 Oct 2009 17:39:56 +0000, rich <rich@nohome.com> wrote:

> On Sat, 31 Oct 2009 09:41:35 -0700, Rick wrote:
>
>> I generally use avidemux to edit a video, but I'm not happy with the
>> quality of the compression that it does. I've tried both the fixed and
>> variable bitrate compression options.
>>
>
> You want to make the file size smaller by about 10% (I think ????)
>
> Try in avidemux
>
> open the source file
>
> set the video format to MPEG-2 requant in the configure option set the
> shrink factor to 1.1
>
> set Audio to copy
>
> set Format to MPEG-TS(A+V)
>
> save to a new file.
>

It worked perfectly! And with no noticeable loss of quality.

I was also surprised at how little time it took. It was much faster than
the one- or two-pass encoding options.

Many thanks!

Rick