Newbie needs advice on Capty MPEG Editor EX

[ezlxq]

I've had a good look through the forums but nothing useful has appeared. Provided I'm using the right search terms, of course....

I just invested in Pixela's Capty MPEG Editor EX, having seen promises and reviews that it can do frame-accurate editing of MPEG-2 source material. Well, yes and no: it won't let me set in and out points within the same GOP. Oh no; I need to trim a single frame from some MPEG-2 source material.

When I carefully read the fine print in the Capty FAQs, I find this:

"To create precise cuts and smooth transitions, it is necessary to move beyond GOP-level editing to frame-by-frame granularity. In the case of MPEG data streams, this requires decoding of the MPEG file’s GOPs into a sequence of uncompressed frames, which are then edited by the user as desired, then reencoding the frames into GOPs so that the advantages of MPEG compression are regained."

Could somebody tell me how I decode the GOPs into a sequence of uncompressed frames, and, more to the point, what I decode them to? I have MPEG Streamclip and MPEG Works, but neither seems to offer a suitable transcode.

(I am not at all happy with the forthrightness of Pixela's advertising. In this case it verges on the deceptive.)

[rumplestiltskin]

Yeah; Pixela is infamous for this.

The reason you have to decode is because compressed video contains a keyframe (which has the entire frame's worth of information) and the subsequent frames between the keyframes (which contain only the changes to the keyframe. Hence frame-accurate editing must be done using some method of decoding the video back to an uncompressed format, editing there, and re-compressing the result.

If you're comfortable with MPEG Streamclip (and it's a wonderful app!), get the Apple MPEG2 playback component (I think it's $20 or $30 as a download directly from the Apple Store) {if you don't already have it} and export the video to DV or even uncompressed video. Although DV does have a bit of compression it does permit frame-accurate editing (and you already have iMovie, right?).

As MPEG Streamclip will let you set in/out points, try a few different exports of a short clip and see how things work.

[Frobozz]

That's the explanation of what Capty MPEG Edit EX automatically does when you edit in the Frame List rather than in the GOP list. It decompresses the GOPs that are in the edit area, trims the frames and re-encodes and joins the MPEG 2 file with new GOPs. However, it doesn't let you set both the in and out points within the same GOP.

You'll need to export your video to DV and to do that edit in a different application.

[pepegot1]

Try VideoRedo-Great program and customer service.

[ezlxq]

Thanks, guys.

And that last suggestion is exactly what I've done: I invested in VideReDo and it works just fine! I run it on my Intel-powered Mac under XP hosted by Parallels.

So here's a warning regarding Capty MPEG Edit EX that future searches may fine: this app cannot edit within a GOP. Don't buy it if you need to make less-than-GOP-size cuts, because it may not be able to do the job.

[JoachimS]

MPEGStreamclip:

You can use "Go to Keyframe" when editing. It is usually precise enough to delete some commercials.
It places the cursor to the closest keyframe where you can place your in and out markers.

[Herve]

this app cannot edit within a GOP.

No app can edit within a GOP (without transcoding)
A GOP is:
- a "jpeg" image (I frame)
- differences from image I to next information (P frame). REM: it's not an image, just "which pixels moved since the I frame)
- next P frame contains differences between previous P frame and next P frame, etc (and always, less than an image, just modifications)
- B frames are between I and/or P frames (just to sweet the motion)

so you'll have a begining (then a possible cut) only at the begining of a GOP
if you cut elsewhere, you cannot have a whole image (just some information) = some very cool Green blocks to replace the missing infos.

PS: if you trascode (eg: for DV), you'll can edit the movie frame by frame, not with MPEG2
PSS: in france, satellite streams have very long GOP (>1second), then you cannot cut less than one second

bye