re-encoding mpeg2 files at lower bit rate.

[stniuk]

Hi,
I have searched the boards a number of times but can't find an answer:

At the minute if your movie is > 4.5gb and you want to back-up to DVD-R you must convert to quicktime (after extraction) then import to final cut pro then export as mpeg2 at a lower bit rate for dvd studio pro to build the disk. This takes a long time and a huge amount of disk space and sometimes does not work. A simpler solution would be to re-encode the mpeg2 file at the lower bit rate. Is there a mac appliction that can do this?

Does ffmpeg do this? If so how?

Thanks for any help

[a9702466]

Hi,

This will only work on Mac OS X - forget any other OS!

- Install OSex (http://mac.mercy.bei.t-online.de/svcd/software/OSEx-0.0110a1.sit) and rip the video and at least one audio stream (m2v, ac3)
- Install Developer Tools
- Download MediaPipe (http://mediapipe.sourceforge.net/)
- Install MediaPipe
- Compile MPEG Encoder using shell:

cd /Library/MPipe/MPEGEncoder # switch to Libraries
# or
# cd ~/Library/MPipe/MPEGEncoder
ls -l # List content of directory
# now you have to build it using the inlying shell-skript - I don't have
# the name in mind

- Start MediaPipe
- "Set Destination" to folder where the output should be stored
- Add pipe "File Browser" and pick the m2v file
- Add pipe "File Streamer"
- Add pipe "MPEG Decoder"
- Add pipe "Color Conversion"
- Add pipe "MPEG Encoder" and use the "Configure" button to set the attributes
- Start the process
- Is this done you can use f.e. DVD Studio to author the disc

I hope this is not to confusing

[stniuk]

Sorry about the delay in answering but I didn't have a chance to try it until now.
I tried the steps you descibed and it seems to work. I will do a bit more experimenting. It only took about 12hrs on 800mhz G4 but this is better that 2 days and lots of hard drive space using the previous method.

I was wondering about bit rate maybe someone knows the calculations for estimating file size.

I thought it may go something like this but it does not seem to be working out:

example film length = 100 mins = 6000secs
encoding bit rate = 9800000 bits/sec or 9.8m bits/sec
total bits = 6000*9800000
total bytes = total bits/8
k bytes = total bytes/1024
m bytes = k bytes/1024
g bytes = m bytes/1024

Well I must be doing something wrong as the result is always too large. Is the bit rate variable?

Knowing the file size would help when mastering a DVD.

Thanks for any help.

[erzimeriah]

i don't know if the bitrate is variable, but i do know that the code a9702466 gave is very confusing to me. i've tried it and cannot get it to work at all.

maybe you could explain it again, a little more in depth?

[a9702466]

for stniuk:

bitrate example:
movie-len: 76 min -> 4560 secs
audio-size: 2 ac3-streams per 107520 kB
dvd-capacity: 4.3 GB -> 4403.2 MB -> about 4508876 kB

video-capacity = dvd-capacity - ac3-streams = 4508876 - 2 * 107520 = 4293836 kB
kB-rate/sec = video-capacity / secs = 4293836 / 4560 = 941.63
kb-rate/sec = kB-rate/sec * 8 = 7533,04

this is the average "kilo-bit-rate-per-second"!

for erzimeriah:

the bitrate is variable. but for calculating it doesn't matter wether it is or not. just the quality of the result differs!

what exactly is doesn't work?

[erzimeriah]

i guess i'm confused about the shell compiling for the mpeg encoder. is this a code i need to type in when i add it to the pipeline?