Why shouldn't I edit an MPG file?

[mikewg]

I hear people saying that I should avoid editing an MPG file at all costs. For me, it's easier to convert the AVI to MPG first and then edit out pieces and group other pieces together. Is this bad? Can someone explain to me why I shouldn't do it and what's a better way to do it? I hear about FrameServing from VirtualDub to TMPGEnc, but I don't know what that means or how to do it.

[suriyan]

Hi,
That advice is really good. I am kind of learning it the hard way. You see, I am trying to make a vcd of songs. With menus letting you select any song. I converted the songs to mpg. Next I wanted to cut them so that I can add some fancy transitions between songs. To help me do this, I needed to cut them at the frame level.
I tried Myflix, Ifilmedit, Mpegvcr etc etc. With Myflix I was able to cut properly, but it is not recognised as a VCD anymore, no matter what I do (demux -> mux again or use vcd gear). Ifilmedit cuts at weird places and for long mpegs the sound goes out of sync. Mpeg vcr does a good job, but it had problems with recording the clip as it would start looping halfway in the song, and hence on saving the clip saved it only till the section where it started looping.

I am still trying ...

Regards

[ktnwin]

These are the reasons:

1) tools to edit AVI (DV format, not Divx) are widely available and easy to use. Tools for MPEG editing are scarse if it works at all.

2) editing MPEG files will cause re-encoding (.e.g. when transitions are added), the cause a serious loss in quality.

I have tried to re-encode an MPEG file to a second MPEG file (same resolution and bitrate as the first), the second looks terrible compared to the first.

[RaleighNC]

A newbie answer. Yeah the problem is where the cut is made.

I converted my first divx to mpeg1 yesterday using vdub and it worked well, but slower than avisynth/frameserver.

First you need to run AUXSETUP.EXE>>install handler>>OK. Then merge the \vdub\aviproxy\proxyon.reg file (rightclick>>merge) to the registry.

Run vdub>>load avi file>>edit if needed>>start frame server>>hit OK on next question>> sav .vdr file as an .avi extension (test.avi)

Start encoder>>load fake avi(test.avi)>>configure/load template>>start capture of video file only (mpv/m2v).

After video capture, go back to vdub>>file>>save wav file. For me, I edit the wav file to make sure i didn't capture the next clip or commercial.

After wav, tmpeg with toolame plugin>>load wave file>>create mp2 file.

Using bbmepg, start button>>settings>>load input files mpv & mp2 files>>output test.mpg>>set mpeg type>>start mux.

So instead of cutting and REencoding, I am just encoding the clip with s/vcd setting already. I can merge them all together with tmpgenc's merge/cut or (still reading) making chapters on s/vcd.

[tigeroolfd]

If you are only doing cutting and joing (for example, to get rid of the commerical), then it's fine to edit with a MPEG2 file. But if you want to add any transition to between parts, then do it using AVI.

[mem_user]

I dont know what the big deal is. I use a simple store bought program called Video Studio 5 to edit Mpeg 2 files. It does not do anything to quality when I add trans between takes. I then use VS to re-encode to a svcd using their setting and burn it with the DVD plugin and my svcd's look great. At least in my opinion. Now these are not DVD rips that I am converting, but the are video from my D8 camera. The mpeg2's are created using DVC II. Like I said, just my opinion.

[speedy]

The reason you avoid re rendering is because MPEG is a compressed format. It is a matter of diminishing quality. The more times you compress (render) a MPEG file the lower the quality becomes and the more artifacts you'll introduce. It is basically the same reason you should never redo a JPG image...its the compression. Compressing a file that has already been compressed in a no-no if you care about quality.

That all said you can actually improve the "quality" of a mpeg file if you first render it as a uncompressed AVI, then apply whatever filtering you want rendering as a 2nd AVI then lastly save the second AVI as a MPEG.

[mikewg]

So if all I want to do it trim off the beginning and end of the MPG (getting rid of commercials) or joining MPGs together, then that's fine to do in MPG format? And anything else I should do as an AVI format? I just want to be sure it's okay to use TMPGEnc to join and clip MPG clips without messing up my VCD settings or the quality.

[speedy]

Works for me. The issue would be does your encoder actually re render if you just stip off the front or end portions. It should not assuming you don't change bitrate, add filters or anything. The tip off of course would be the time to process should be much shorter as compared to a file of similar size where you do make lots of adjustments.

[Anonymous65]

Simple cuts and trims also depends on the editor. If the editor does NOT re-encode the mpeg stream, then you're fine. However, if it does re-encode, you loose quality, especially if you're editing a VCD file. However, there are a few editor that does NOT re-encode the file, like Cineplayer Editor. It's the only one for Mpeg-1 files I have found that will cut and joing VCD complinat files WITHOUT messing with the mpeg stream. No demuxing, remuxing is needed, and no quality is lost.

[eatin sammiches for lunch]

remember de and re-muxing are not the same as reencoding....mpeg editors demux but re-encoding is not neccessary if u just do a simple frame clipping..only time when u need to re-encode is when u want to edit the stream(resolution,bit rate.etc.)

[Anonymous65]

Many editors will re-encode even when doing simple cutting and trimming. Do a trial and see how long it takes to save your trims. If you can save a 1 hour mpeg file in a few minutes, it's not re-encoding the file. But, if it takes an hour or longer to save the project, it is re-encoding the file. Or simply see if the quality is worse after you edit the file. Also, with some editors you have to demux and remux to get a valid mpeg stream after editing (and yes, muxing is simply organizing the data, NOT re-encoding it).