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Trimming/Splitting clips

 
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NCF



Joined: 27 Apr 2003
Posts: 4
Location: Brazil

PostPosted: Sun 27 Apr 2003, 20:45    Post subject: Trimming/Splitting clips Reply with quote

Hi,

I'm looking for some software that could split my footage automatically based on some sort of scene detection. My footage is already in MPEG-2 with 720 x 480 and audio PCM 44100 stereo (a little odd figure, I guess).

Is there any software available that could split a GOP and recreate it without having to render all subsequent GOPs ?

This question may sound silly, but I'm could not locate any written reference on how to split one GOP e recreate 2 new GOPs in its place (one for the end of the previous scene and the other for the beginning of the next scene). Is that possible?

Thank you in advance for any information you could give me on this subject.

(NCF)
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RMN
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Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Fri 2 May 2003, 1:22    Post subject: Reply with quote

Any decent MPEG editor will keep the original data when possible (recompressing only GOPs that have been broken). I think this is how TMPGEnc's "MPEG Tools" (in the "File" menu) work. But you have to set the in and out points manually.

The tricky bit there is automatically splitting the file on scene changes. Assuming such a program existed, I suspect it wouldn't work all that well. The "scene detection" algorithms in most programs are based simply on image changes. So if someone walks past the camera, or if there's a flash, etc. (something that makes one frame very different from the previous frame), they would consider that the scene had changed, and would split your file in two.

I can think of a few tricks to make the algorithms more accurate, but I don't know any program that uses them.

RMN
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NCF



Joined: 27 Apr 2003
Posts: 4
Location: Brazil

PostPosted: Fri 2 May 2003, 3:22    Post subject: Reply with quote

I guess you're right. I've been playing around with TMPGEnc Plus and M2 Edit Pro 5 and they both allow me to split and trim my clips with no pain. Maybe the Adobe PremiƩre 6.5 was misconfigured when I tried to process the file (slightly different settings between input and output files). The M2 Edit Pro 5 scans the entire file and splits it based on scene detection. You can fine tune its sensitivity for this job, but it makes some mistakes as you correctly pointed out.

By the way, I noticed that you like TMPGEnc a lot based on your comments. Could you explain why I cannot open a MPEG-2 file with TMPGEnc Plus (error msg: cannot open or is unsupported) if this very same file is opened by its MPEG tools, splitted, trimmed and the output saved with no error message?

Cheers,

(Nestor)
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RMN
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Joined: 04 Feb 2003
Posts: 587
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PostPosted: Fri 2 May 2003, 18:49    Post subject: Reply with quote

I think that the latest versions of TMPGEnc don't include a MPEG-2 decoder (they mentioned this in the release notes some time ago). This is probably due to the fact that the MPEG consortium started charging a small fee. As long as you have a MPEG-2 decoder installed in your system (ex., PowerDVD's), TMPGEnc should be able to open the files.

If you have a MPEG-2 decoder installed and still can't open the files, go to TMPGEnc's "VFAPI plug-in" configuration and set the DirectShow reader's priority to the top. Remember to set it back down afterwards, because Directshow has problemns with some AVI files (which work better if you open them with the OpenDML / VfW readers).

RMN
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NCF



Joined: 27 Apr 2003
Posts: 4
Location: Brazil

PostPosted: Sat 3 May 2003, 14:01    Post subject: Reply with quote

I thought the license was required only for encoding. I read the terms of licensing some time ago and I recall some weird rules. For example, after you encode your main footage, you are allowed to encode another footage for free as long as you don't exceed 12 minutes... that explains some extras that come along the DVD which are shorter than 12 minutes...

Anyway, I tried what you suggested but it seems I don't have a software decoder for MPEG-2 installed. I'm using the ATI All-In-Wonder Radeon 8500 (128M) and they have MPEG-2 decoding and encoding acceleration in hardware.

On a second thought, how the TMPGEnc Plus can process (demux, split and merge) an MPEG-2 program if it doesn't have a decoder or can't access one on my PC? You may say that it does not need to decode the image because it can slice the GOPs based on header contents, but the TMPGEnc is showing the actual images in the merge window! Doesn't this sound strange to you?

(NCF)
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RMN
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PostPosted: Tue 6 May 2003, 16:25    Post subject: Reply with quote

Yes, it is strange. As you said, the licensing of MPEG-2 is very weird. I suspect several programs are actually in violation of the license, but the MPEG consortium doesn't seem interested in going after them (probably only cares when some big company tries to get away from paying the licensing fees). TMPGEnc must have a built-in decoder (I mean, if it has an encoder, how hard would it be to include a decoder?), but for some reason (which I suspect has to do with licensing) it will not open MPEG-2 files directly, and instead must go through DirectShow.

Anyway, the ATI hardware decoder should be able to work as a system codec, so perhaps there is a way to load the MPEG-2 files into TMPGEnc. Try changing the MPEG-2 file extension to .MPG. This could be required by the ATI codec (although I have no problem opening files with a .M2V extension in my system, using the PowerDVD decoder).

By the way, where did this file (the one you cannot open) come from? Was it encoded by TMPGEnc? Have you tried opening MPEG-2 files from different sources? It could be some issue with that specific file (or some detail in that file's headers).

RMN
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NCF



Joined: 27 Apr 2003
Posts: 4
Location: Brazil

PostPosted: Wed 7 May 2003, 0:36    Post subject: Reply with quote

Well, I'm quite sure TMPGEnc has a built-in decoder to play the MPEG-2 files in the "MPEG Tools" section.

The ATI codec, if it exists, must be buried inside their applications. I could not locate them anywhere in my system. The files I'm working on were created by ATI's Digital VCR application, and have .MP2 extension. I can play them on ATI's Player, Microsoft Media Player, open them with Adobe Premiere 6.5, M2 Edit Pro and several other programs for DVD authoring. I also tried to change the extension as you suggested, but to no avail.

The first time I installed TMPGEnc Plus I also installed the DVD Authoring package from Ulead, and the TMPGEnc accepted the .MP2 files without complaining. Maybe the Ulead codec was in charge of decoding the MPEG-2 program for TMPGEnc at that time.

Have you ever tried to contact the people that developed the TMPGEnc Plus? If so, have you received any reply from them? I've been playing around with MPEG-2 files for a while and would like to suggest some (humble) improvements to their program.

Cheers,

(NCF)
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RMN
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PostPosted: Wed 7 May 2003, 22:53    Post subject: Reply with quote

As far as I know, TMPGEnc is made by a single person (Hiroyuki Hori), and I haven't found any way of contacting him. You can try sending a message to Pegasys (the company that sells TMPGEnc), but in my experience the people in their tech support are... what's the word... clueless. Mr. Green

Here is what I managed to find in TMPGEnc's release notes. I've emphasised some parts that make me believe this is a licensing issue, and not exactly a technical one.

Quote:

Note for Specification Change in TMPGEnc Plus 2.57

+ Opening an MPEG file with TMPGEnc Plus

Because the current version of TMPGEnc Plus does not have its own MPEG-2 decoder feature, it relies on other MPEG-2 decoders installed onto Windows system through Microsoft DirectShow to read MPEG-2 file.

As standard Microsoft DirectShow does not support playback of MPEG-2 files, but it is possible to playback MPEG-2 files by installing a DVD player.

Even though Microsoft DirectShow, by installing or having additional component of DirectShow, extends capabilities to read/playback other formats, this is completely dependent on the software installed on your system, and it may sometimes be unstable because of compatibility or conflicts between such additional components. Therefore, we do not officially guarantee the ability to read the movie files via Microsoft DirectShow.

In this case movie files include, AVI (Type1 DV format), .mpg (MPEG-1/2), .asf, .wmv, and .mov.

Although there are so many MPEG-2 decoder, which can be installed onto Microsoft DirectShow, not all of them can be used with TMPGEnc Plus. There are several decoders which are

- not stable, as a result TMPGEnc Plus appears to be unstable as in the previous version.

- not allowing other application to use the module, and as a result, TMPGEnc Plus can not read the movie file.

TMPGEnc Plus 2.57 reads MPEG-2 files only with specific official commercial legal MPEG-2 decoders made by CyberLink, Ligos, and Sony. Therefore, TMPGEnc reads MPEG-2 files best by operating these decoders directly from TMPGEnc Plus. In this way, it improves the stabilities to read files, but only if one of these 3 decoders is installed on your system. Other decoders cannot be controlled by TMPGEnc Plus.

There are at least 2 type of bitrate allocation, one is CBR, the other is VBR, but Microsoft DirectShow is only able to seek MPEG files encoded in CBR, and therefore TMPGEnc cannot do "Cut editing", which needs accurate file seek if the MPEG file is in VBR. For example, if the file was encoded in VBR, audio or video may be stopped for a while at the point you cut.

If Microsoft Windows Media Player cannot open a movie, TMPGEnc Plus can not open the movie either.

- Sony MPEG-2 decoder may be preinstalled in VAIO RX models etc.

- There may be cases where an MPEG-2 file can not be played through Microsoft DirectShow because of the decoder's specification even though a DVD player has been installed.

+ MPEG files which can be edited with MPEG Tools in TMPGEnc Plus

There is a tool called "MPEG Tools" in TMPGEncPlus. This tool enables the user to de/multiplex audio and video or to cut/merge movies. These operations are done in binary level, and therefore there is no re-compression.


There are several types of software that produces MPEG files, which are not in MPEG standard, and such files can not be edited with MPEG Tools in TMPGEnc Plus. TMPGEnc Plus's MPEG Tool only officially supports MPEG files, which were encoded with TMPGEnc Plus. MPEG files made by other software/hardware might be edited, but we are not able to support/warrant the result officially (please read the note below too).

In "Cut" of "Merge & Cut" in MPEG Tools, it uses Microsoft DirectShow to show preview and determine the positions to cut. Microsoft DirectShow can not seek MPEG files correctly if files were encoded in VBR, thus, start and end positions to cut may not be accurate. The actual position to be cut may not be the one, which is displayed in the window, and so, even an MPEG file that is encoded TMPGEnc Plus, if the MPEG file was encoded in VBR, may not be cut accurately. We are not able to warrant the results on this matter as well as the case in previous column.

The Merge & Cut always deals with scenes by GOP (Group Of Picture), and standard MPEG files has about 15 frame in 1 GOP which is about 0.5 sec. If the start/end point you selected to cut is not close to the boundary of GOPs, the point will be automatically moved to the closest boundary of GOPs.


Apparently, TMPGEnc will only open MPEG-2 files if it detecs a "legal" commercial decoder made by Sony (Vaio PCs), Cyberlink (PowerDVD) or Ligos (LSX).

Also note that, apparently, the "MPEG Tools" will not cut GOPs. I don't know if this applies to all files or just to files that were not originally encoded with TMPGEnc.

Again, I suspect this has to do with licensing (to cut and re-compress a GOP, TMPGEnc would have to decode the image and re-encode it, whereas to cut only at the GOP boundary no decompression is necessary). Obviously, if TMPGEnc includes code to compress video to MPEG-2, it would be trivial to include a decompressor.


RMN
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