2 Replies Latest reply on Apr 9, 2010 9:33 AM by anonmous

    Comparing two video clips



        I have an AVCHD file that needed to be trimmed (by trimmed, I mean I wanted to remove all the content after a certain point, but not need to re-encode what remained).  I was able to do it, but to test as to whether the trimmed version had been re-encoded, I decided to put both the original AVCHD content and the trimmed AVCHD content into a Premiere CS4 sequence with just the video track from the original in track 2.  By setting the blend mode of track two to 'Difference', it appears that up until a handful of frames at the very end (I expected this unless I happened to trim right on an I-Frame border) the two tracks are identical.  I guess I could also open the two files with a hex editor to be sure, I might do that.  But, if I weren't comfortable with a hex editor, is utilizing the Difference blend mode a reasonably good way to do this type of validation?





        • 1. Re: Comparing two video clips
          Colin Brougham Level 6

          That's what I do, though usually with DV source clips. Many times, I have to capture footage into FCP from BetaSP, and for my purposes, capturing to QT DV is just fine. However, I do my editing and output on PC-based Premiere systems. Whether it's because it's FCP or Beta or the BlackMagic card used for capture, many times I'll end up with a number of files due to "timecode issues". I'll usually capture a bit of overlap, move the files to Premiere, drop them all in a timeline, and trim the heads and tails to create what is essentially one long unbroken capture. Premiere handles the MOVs just fine (no red render bar), but to make management a little easier, I'll export either a fresh QT DV MOV or an MS DV AVI.


          Just as a confidence check, I'll bring the exported clip back into the project, lay it on a track above the trimmed clips, and flip to Difference. I've never seen anything but a solid black frame (regardless of the format I export to), and you can also set the display to YC waveform, where you should see nothing but a solid line at 0IRE. This indicates there is no difference between the two clips.


          Now, I'm guessing you did you trimming in Premiere, and then exported back out to H.264. I was not aware that Premiere did smart-encoding with any sort of MPEG-based assets and exports; I know there are plug-ins available to do this (MainConcept has one, I believe). So, I'm actually surprised that you're seeing only a few frames where reencoding occurred. If this is indeed the case, I'd call it good enough; at some point, you're going to be introducing compression or recompression anyway, so a little is to be expected. If you trimmed in another application, though, do tell...

          • 2. Re: Comparing two video clips
            anonmous Level 1

            Hi Colin, thanks for the tip about changing the display to YC Waveform, I never would have thought of that.  When I changed the display to YC Waveform, I did have a solid, unchanging flat line right below 10, but when I unchecked the 'Setup (7.5 IRE), the line was at 0 throughout the entire sequence except at the very last 30 or so frames where it bounced between 0 and 5 (in normal viewing mode these last 30 frames show as almost solid black, only a few white 'blips' or 'streaks' appear).


            To answer your question, no, I did not use Premiere to do that trimming.  If there is some capability within Premiere or AME which can do this (without reencoding) please do tell!  I spent many hours searching for a free solution and didn't find anything other than TSSniper.  I downloaded it and it was unusable on my system  so I had to abandon it.  Mind you, I can edit and playback AVCHD with multiple Premiere effects applied to as well as AE dynamic link sections with no problem, so I don't it's a problem with my system's specs.  What I was ultimately hoping for was some sort of workflow using AviSynth and VirtualDub to be able to trim, but I couldn't find any workable solution.


            What I finally, grudgingly ended up doing was installing the OEM software that came with my Canon, Pixela ImageMixer.  It's largely bloatware junk, *but* it does allow me to trim without reencoding the MPEG-4 stream.  If there's any other way to accomplish this that somebody is aware of, please do tell.  Ever since I installed the Pixela stuff, if I run it to do some trimming (thankfully, this *should* be rare), then some strange window focus stealing process infects Premiere CS4 (as well as Pixela itself and essentially all processes) so that I have to shut down Premiere (and any other app where focus is relevant) and the Pixela atrocity.  By 'focus stealing' I mean this:  typically, when one clicks the 'Play' button in the Program Monitor, the sequence will play until it either ends or you click outside of Premiere or another window pops up to take the focus away.  Well, with the Pixela gremlin, the focus will be stolen from Premiere every 1 or 2 seconds (it's probably a hidden window popping up from time to time).  See why I don't like OEM software?