Splitting A ProRes File - Without Re-Encoding?

[User]

I started with AVCHD and transcoded to ProRes 422. Now I want to split the clip while keeping it as ProRes 422 without having to re-encode.

I imported the ProRes 422 file into MPEG Streamclip, marked in/ out points, exported as ProRes 422. Has the file been re-encoded?

[Syme]

Did it export really fast? Splitting without re-encoding should be about as fast as making a copy of the result. I don't know about MPEG Streamclip in particular, but that's a good way to tell in general.

[User]

71 views and only one response. Really?

[mercer]

See if QuickTime will play the file. If it does, then it converted it as well. 

But if you want to trim the clip you already transcoded, then make sure you are working with the new clip... Assuming you renamed the clip and saved it to another folder. 

[Axel]

ProRes is an intraframe codec. That means if you don't change anything within the frame itself, grade it or resize it, there will be no recompression.

[User]

2 hours ago, Axel said:

ProRes is an intraframe codec. That means if you don't change anything within the frame itself, grade it or resize it, there will be no recompression.

Thanks Axel!

Can anyone kindly confirm?

[Turboguard]

I don't know about the program you're using, but both in Premiere and DaVinci when I edit ProRes and then output as same it takes less than the clip length to output. Also, just look at the clip and see if it's what you wanted?

[Axel]

22 hours ago, User said:

Thanks Axel!

Can anyone kindly confirm?

 

16 hours ago, Turboguard said:

Also, just look at the clip and see if it's what you wanted?

You probably read the book DV Rebel's Guide by Stu Maschwitz. He said in order to maintain quality you should never recompress. I think it was an own chapter with capital letters:

NO RECOMPRESSION

Therefore he recommended to use DV (an intraframe codec as well) only as acquisition codec and to encode to *uncompressed* immediately before any further changes were made (referring to changes to the pixels, not simple cuts).

That was in 2006. Now ProRes is not uncompressed and it's lossy, though 'visually lossless'. Surely after some generations compression artifacts will show, I don't know when. I don't worry about generations though if I stabilize and denoise my clips and re-import them before making the Resolve-roundtrip (don't have Studio and don't have the Neat plugin for Resolve). 

With interframe codecs, the image is always completely recompressed. So-called 'smart rendering' isn't smart. Depending on the data rates and the profiles, you will *see* compression artifacts not later than in the third generation, sometimes in the second. This could be called 'visually lossy'.

[tupp]

I think that ffmpeg can separate parts of the clip without re-encoding.  Such a command might look something like this:

Quote

ffmpeg -ss 00:01:32 -t 00:00:17 -i input_video.mov -c copy output_video.mov

"-ss 00:01:32" means the "start second" (or start time) of the new video is at 1 minute and 32 seconds in the source video

 

"-t 00:00:17" means to record 17 seconds from the start time.

 

"-c copy" means copy all video and audio streams (with no encoding).

 

[User]

Thanks again Axel.

So if I understand you correctly, when splitting an interframe codec such as ProRes, there will always be re-compression regardless of the software used. And that compression will eventually lead to artifacts that may of may not be visible after one or more generations.

Can someone actually confirm this as well?

Sorry to keep coming back at it but my remaining question: is there 'newer' software that does not re-compress ProRes when a file is split apart?

[tupp]

7 minutes ago, User said:

So if I understand you correctly, when splitting an interframe codec such as ProRes, there will always be re-compression regardless of the software used. And that compression will eventually lead to artifacts that may of may not be visible after one or more generations.

Fairly sure that ffmpeg can split files with interframe compression without any re-encoding (thus, no re-compression).  It might want to position the splits at the I-frames, but it still allows parts of a file to be copied without re-encoding.

 

Pretty sure that mencoder can do the same:

Quote

mencoder -endpos 01:00:00 -ovc copy -oac copy input.mov -o first_half.mov

mencoder -ss 01:00:00 -oac copy -ovc copy input.mov -o second_half.mov

 

[Axel]

You mix up interframe (images referring to frames only partially described long before within the GroupOfPictures, backwards and forwards, with variable data rates affecting the precision with which individual pixels are stored) with intRAframe (individually stored frames, variable data rates due to complexity of the individual images).

I state you can completely neglect recompression artifacts with ProRes.

[User]

Thanks for the input Tupp. My only concern is that you using words like "I think' and "Fairly sure' and this does not exactly inspire great confidence.

It would be beneficial to have an authority weigh in with fact. I have a lot of material in front of me and it would be good to know for sure and get this right.

I will see what info I can find on ffmpeg.

Axel:
I state you can completely neglect recompression artifacts with ProRes.

Sorry but if I understand your English correctly, do you mean to say that: 'the re-compression artifacts will be negligible using ProRes'.

[User]

Yes, it seems that ffmpeg can split files without re-encoding. Now if only I can figure out the correct terminal commands Thanks Tupp. 

[KrisAK]

For what it's worth, Resolve (free) and Premiere both support functions called "Consolidate Clips" or "Consolidate Project.". Throw your long clip(s) on the timeline, cut out the crap you don't want, then run "Consolidate Clips": it will stream-copy only the used material to an entirely new folder of your choosing. All in a friendly UI.

This works for me on Windows, and I know it's lossless because Windows doesn't have a native ProRes encoder, and I don't have one of those third-party encoders.

Regardless of the method you use, you can check for generational loss by syncing the original and copied versions on two video tracks in the timeline, then apply a difference filter. What you're left with is the pixel-level generational loss that's occurred (if any) during the copy.

 

[User]

Good option KrisAK. Thanks.

7 minutes ago, KrisAK said:

This works for me on Windows, and I know it's lossless because Windows doesn't have a native ProRes encoder, and I don't have one of those third-party encoders.

And if I understand you correctly, you are saying that you know that clips are only 'copied' or 'consolidated' and not re-compressed because the ProRes encoder is not on your system. Right? But what if you are on a Mac with PPro and ProRes and you did the same... would it consolidate clips by re-encoding with ProRes because it has access to the script?

[KrisAK]

User: yes to your first question.

As to the second, sorry, but I don't have access to a Mac. (The two-track filter trick should work, though, to check for lossy-ness.)

[KrisAK]

Oh, just to clarify, in Resolve 12 the consolidate functions have been relocated/renamed to "Media Management."

[tupp]

3 hours ago, User said:

Thanks for the input Tupp. My only concern is that you using words like "I think' and "Fairly sure' and this does not exactly inspire great confidence.
It would be beneficial to have an authority weigh in with fact. I have a lot of material in front of me and it would be good to know for sure and get this right.

Just try it -- ffmpeg is free and open source.

 

Here is a tutorial on an easy way to install ffmpeg (with extra codecs) on a Mac, using Homebrew.  Here is another tutorial on how to manually install ffmpeg (with extra codecs).

 

The ffmpeg command to split a file without re-encoding is fairly simple, because one is merely copying the video and audio.  It is probably easiest to use a separate command for each part of the file desired.  So, the ffmpeg commands to split a five minute file directly in half will be something close to these:

Quote

ffmpeg -ss 00:00:00 -t 00:02:30 -i input_video.mov -c copy first_half.mov

ffmpeg -ss 00:02:30 -t 00:02:30 -i input_video.mov -c copy second_half.mov

 

 

 

 

 

 

[User]

Thanks Tupp. I've now got ffmpeg and will have a look at your tutorial on the road ahead