On Sat, 16 Aug 2003, Maik Holtkamp wrote:
> I already had a discussion on the dvdauthor list
> (http://sourceforge.net/mailarchive/forum.php?thread_id=2942599&forum_id=13261)
> on this topic, so sorry if doubled for someones.
I'll give the same advice here that I've given in the past on
the dvdauthor list:
Use a single file.
More about why this is necessary later on.
> I tried to make dvd5 from my dvd9. It is no problem when I use one
> big file, but it will facilitate things here, if I could just use
> chaptering:
That is not the way DVDs work ;(
DVDs are _track_ oriented. Each file goes into a track (sometimes
called a "title or titleset"). Chapters within a title/chapter
play seamlessly as you have discovered - but transitioning across
a track boundary is not seamless.
> transcode -i /dev/dvd -T 1,$I -x auto,null -V -y mpeg2enc,null -F
> 8,"-c -b 8000 -q 6" -o track$I [1][2]
>
> Viewing the single streams with mplayer I receive at the end of
> _some_ streams:
>
> a52: CRC check failed
> a52: error at resampling
I believe that is harmless and simply means the last few bytes
of an audio packet were not written out to the file.
> As I have some problems when authoring the DVD from single files to
> the effect that the picture at _every_ new chapter get frozen for some
> ms, I am interessted if this issue is probably base on mpec2enc or
Each file goes into a separate track/title. Jumping from
the end of one track to another is not the same as playing thru
one chapter into another within a single track.
There is nothing mpeg2enc can do about the situation. It is
an authoring tool and/or DVD design issue. dvdauthor would
need to add a "jump to track N+1" at the end of track N - and I
am not sure if that would be seamless or have a brief pause. I
believe there would be a brief pause - have you ever noticed that
at the end of a movie there is a brief pause before the next menu
gets displayed again? I think that is the "seek to next track"
happening.
Using large files and chapters really is the way to create a DVD.
> [1] In spite of really understanding what -c is for, man page sounds
> promissing for me.
Are you creating DVDs with multiple angles in the video stream?
If that is not what you are doing then do not use '-c'. Creating
closed gops increases the size of the file by a small amount
(~1%) but does not change how tracks and chapters work.
The primary use of -c is to create video streams suitable for
multi-angle DVDs. Oh, and it is required that all video streams
have the same GOP size for all the angles - thus using -g and -G
to set a fixed GOP size will also be necessary.
> [2] Is there any chance to roughly estimate how the resulting
> file-size will be reduced when:
> decreasing -b for 100
> increasing -q for 1
> in variable bitrate encoding? Or is there a other option I sould
> use in order to get more predictable results?
-b sets the maximum (+/- a couple percent of course) rate
(filesize). This is the upper bound on filesize. Use the
value of -b, add the audio rate, and then add about 2.5% for the
other information written to the stream. Use that total and
multiply by the playing time - that is the maximum size of the
file. Then vary -q according to the desired quality (lower -q
values will cause the file to more closely approach the max
filesize).
As an alternative use constant bitrate encoding ;) Leave off the
-q and simply specify the bitrate according to the desrired
filesize.
What I often do is encode a representative sample, between 5 and
10 minutes worth of data, and extrapolate the final size of the
file.
To partially answer the question decreasing -b by 100 will
decrease the filesize by 100/8 or 12.5kbytes per second. Multiply
by the number of seconds of course :)
The effect of -q is data sensitive and there is not a fixed/firm
relationship between increasing -q by 1. I have seen in some
cases going from 5 to 6 a change in the average bitrate around 15%
but that varies from run to run depending on the data.
Cheers,
Steven Schultz
-------------------------------------------------------
This SF.Net email sponsored by: Free pre-built ASP.NET sites including
Data Reports, E-commerce, Portals, and Forums are available now.
Download today and enter to win an XBOX or Visual Studio .NET.
http://aspnet.click-url.com/go/psa00100003ave/direct;at.aspnet_072303_01/01
_______________________________________________
Mjpeg-users mailing list
[EMAIL PROTECTED]
https://lists.sourceforge.net/lists/listinfo/mjpeg-users
