Application to modify bitrate of an MPEG-2 file

[NoCalME]

Does anyone know of a Mac app. that enables one to modify the bitrate of an MPEG-2 file without re-encoding? DVDPatcher on the PC side has this feature, but I was looking for a Mac equivalent.

The DirecTiVo MPEG-2 files that I use have a 15.0 Mbps bitrate and DVD Studio Pro 2.0 will not import them unless the bitrate is modified and the header is patched to 720x480. I've been successful getting DVD Studio Pro 2.0 to import the modified files using DVDPatcher and Gumby, but wanted to try to eliminate the usage of DVDPatcher to make it an all-Mac process.

[live4ever]

I don't think so.
Anyone else?

[live4ever]

Somethings you could try:

1-Demux the mpeg2 file (bbdemux, ffmpegX, Mpeg2 Works etc.) and see what kind of audio you get. I don't have a tivo but I'm assuming they encode with an uncompressed audio track (PCM). Use APack to encode to AC3 (or mp2 if you like) and this should decrease the overall bitrate by some.

2-15Mbps sounds like the highest quality setting on the tivo. Maybe try recording with a lower setting initially (you will be able to fit more video per DVD this way as well), then try encoding the audio to AC3.

[bilestyle]

u can get gritty and do it in hexedit.... take the file u are attempting to patch and make a copy of it b4 patching, then compare the new file with the old in hexedit.... its been my experience for it to go something like this


good header

00 00 01 B3 2D 01 E0 24 00 02 A1 30 00 00 01 B5

bad header

00 00 01 B3 2D 01 E0 24 FF FF E1 30 00 00 01 B5

u can see for yourself the problematic hex ( FF FF E1, rather than 00 02 A1) now to be honest im not sure what each of those addresses refers to in the m2v header, but once i changed them to the same thing dvd patcher changed them to dvd studio pro accepted the file.... i havent tried building files in this method yet, but essentially i believe dvd studio pro gathers its own information after accepting the file... so if u fix the first faulty header (the header reoccurs several times throughout the file) you should be good to go.

i know this isnt the cleanest solution, but it is all mac


to refer to changing the headers for the sizing (to 720x480) refer to RNC's website

specifically

http://homepage.mac.com/rnc/EditMpegHeaderIFO.html

[pfile]

the 0xFF FF E1 is the bitrate. actually expressed in binary, only the bold part is part of the bitrate.

1111 1111 1110 0001

this is the number 0x3ffff, or 256K. 0x1 = 400 bits/sec, so this number encodes the bitrate of almost 100mbit/sec. DVDSP probably thinks this is illegal.

rather than opening, editing and closing the file with hexedit, i used hexedit to create a file containing the bytes 2D 01 E0 24 00 02 A1, then from the osx terminal you can do the following:

cat file_with_bytes | dd conv=notrunc of=movie_file.m2v bs=1 seek=4

this rewrites just those 6 bytes starting at offset 4 in the file.

now to be perfectly accurate, you probably should not blow away the whole last byte (the A1) because the 6 low bits of that byte mean something else. probably if you just put 2D 01 E0 24 00 02 in the file and run the same command it will work just as well; it probably doesnt matter what the 2 low order bits of the bitrate are, since that will at most change the bitrate by 1600bits/sec... blowing away the FF FF and setting the size to 720x480 (the 24) are the most important parts.

[pusa]

For Mac, use DVD•TFDVDEdit. It's a really cool program to use. I just heard about this program not too long ago.

http://www.lafcpug.org/reviews/review_tfdvdedit.html

[pfile]

um, yeah. TFDVDEdit = $700. dd = $free.