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MPEG2 video tools

 
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shadysamir



Joined: 28 May 2003
Posts: 8
Location: Cairo - Egypt

PostPosted: Wed 4 Jun 2003, 10:28    Post subject: MPEG2 video tools Reply with quote

Does anyone know if there are tools to perform any of the following tasks:
1. Insert I frames at given timecodes in an MPEG2 stream.
2. Stitch MPEG2 files together and split them
3. View GOP information or GOP structure of an MPEG2 file.
4. Transcode a part of an MPEG2 file.
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RMN
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Joined: 04 Feb 2003
Posts: 587
Location: Lisboa, Portugal

PostPosted: Wed 4 Jun 2003, 14:18    Post subject: Reply with quote

1. Not sure what you mean. To insert an I-picture you need to decompress the file and recreate 2 GOPs (i.e., you need to re-encode that segment). This usually results in a loss of quality. It can be done, but the I-picture should have been added in the original encoding.

2. Yes. You can use TMPGEnc's "MPEG Tools" (in the file menu) to do this. As long as all cuts are made at the beginning of a GOP there shouldn't be any loss in quality.

3. Yes, there are several utilities to see this information (ex., Teco Bitrate Viewer).

4. What do you mean by transcode? Encode it again with different sttings? Yes. Most MPEG encoders will let you use a MPEG file as the source. Simply select different output settings and it will be converted. This usually results in a loss of quality, though.

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shadysamir



Joined: 28 May 2003
Posts: 8
Location: Cairo - Egypt

PostPosted: Wed 4 Jun 2003, 14:43    Post subject: Reply with quote

thanks alot for your time with all replies

with 1 i meant to have a final MPEG2 file then just like the encoder would insert an I frame at scene changes a tool would insert an I frame there and restructure the frames in this GOP only. Now that i wrote it all down i dont think it's possible!!

with 4 i meant to select a segment of an MPEG2 file and re-encode this segment (from uncompressed source) using diff bitrate. for example let's say i finished my encoding, the file is prefect for the bitrate i choose. Then there was a scene from 00:01:20:00 to 00:02:15:00 that needs to be encoded with a diff bitrate. Then i can choose in and out points from source, encode it into the old MPEG2 file without having to do the whole job from the beginning...
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Shady Samir
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RMN
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PostPosted: Wed 4 Jun 2003, 18:32    Post subject: Reply with quote

shadysamir wrote:

with 1 i meant to have a final MPEG2 file then just like the encoder would insert an I frame at scene changes a tool would insert an I frame there and restructure the frames in this GOP only. Now that i wrote it all down i dont think it's possible!!


It is possible. But it's not easy to do with TMPGEnc. You may be able to do it in a simpler way with an editing program that supports MPEG-2 (either natively or through a codec).

shadysamir wrote:

with 4 i meant to select a segment of an MPEG2 file and re-encode this segment (from uncompressed source) using diff bitrate.


You want to select a segment from an MPEG-2 file and encode from an uncompressed source...? That's a slightly strange concept. I mean, it's a bit like selecting a segment from one movie and then using a completely different movie for the source. Smile

Just note down the file's timecode (or frame number) for the in and out points, and then use those timecodes on the other file. As long as the source file and the MPEG file have the same starting timecode and the same frame rate, the segments will match.

It wouldn't be very hard to write an encoder that supported proxy files (i.e., use one file to set the in and out points, and then use another file to render), but it's not something that people normally need to do, so I don't think any encoder I know has support for it. Proxies are very common in film animation and compositing, where it's not practical to work in full-resolution all the time (so you use low-res files, and then tell the program to use the high-res versions for the final render).

The closest thing you can do with TMPGEnc is this:

Load the MPEG file as the source. Go to the "filters" and select "source range" (double-click). Set the start and end frames. Go back to the main window and replace the source with the original AVI. The source range should not have been alterted. But as with the timecode approach, this only works if the two files match perfectly.

And note that this will create a separate file with that segment. You'll then have to use the "MPEG Tools", to join it to the rest of the movie.

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shadysamir



Joined: 28 May 2003
Posts: 8
Location: Cairo - Egypt

PostPosted: Wed 4 Jun 2003, 20:57    Post subject: Reply with quote

I know this is taking too long going back and forth but I think I didnt make myself clear. What i meant is the same movie. sometimes i finish encoding on a bitrate for a very long video then i find out that a small part needs to be encoded in a different bitrate. I dont want to re-encode the whole movie using the new bitrate but only this small scene. am i making sense? but again i guess i know what can be done now using TMPGEnc. I should re-encode only this scene then stitch together the three segments below:
1. Movie until inpoint of re-encoded scene.
2. re-encoded scene
3. Movie from outpoint of re-encoded scene until end.

Thanks for your effort and time
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