How many generations of .mp4 till quality degrades?

Report · Mar 30, 2018

I did some tests by taking a .mts avhcd clip and exporting it out to .mp4 with the H264 setting and moved the target and maximum bitrate sliders all the way up. I exported this and put the clip above my .mts clip in premiere and zoomed into 100 percent in the program monitor and turned on and off the video track for the mp4 clip and found no quality difference at all from the .mts avchd clip. I then added a few lumetri color settings and even scaled the clip itself to make it extreme. I exported the .mp4 again with the scale and lumetri color settings to another h264 .mp4 file with the same settings as before in the export window. Low and behold no quality degradation in premiere from the first .mp4 clip.

Question is this. how many more times can I seriously keep exporting a .mp4 clip before degration occurs? Since it appears I can at least export once if not twice from .mp4 I see no reason why I can't convert my AVCHD clips to .mp4 and edit with those which would enable me to label my clips in windows explorer and not have to deal the card structure of the AVCHD files. I do not like it when the clips are unnamed and I can't rename them or the card structure gets broken but if I have .mp4 clips it's easier.

Am I right to assume AVCHD is h264 anyway?

Report · Mar 30, 2018

You can export a clip, reimport, place it above the original in a sequence, and go to "Difference" I think it is in blend modes, and see any pixels that differ one to the other.

With a high bit-rate mp4 export, you might not see much the first generation, but there's a little. Do a second, it gets worse ... fast.

This is why for "digital intermediates" most editors use Cineform, DNxHD/R, or ProRes, in high-quality flavors. Bigger file sizes, but a lot less "lossyness" per generation.

Neil

Report · Mar 30, 2018

well when I turn on different the image just turns black. Is that what I'm supposed to be seeing?

Report · Mar 30, 2018

Do you have any idea how I'd use cineform files on a regular HDD via USB 3 external? So far the timeline plays back super slowly on a laptop with cineform files on a HDD USB 3. If I put them on my 2TB SSD USB C it plays back fine but then of course my SSD fills up quick and then I run out and can not even complete a project. I also tried proxy files via cineform but they are the same file size as high quality it seems.

Report · Mar 30, 2018

Create proxies for the job, delete 'em after. DON'T save the things, of course, as they can be easily re-created. Large, yes, but playback is far easier on the computer. A Samsung T3/5 SSD on that USB3, and you probably wouldn't even notice it was 'external'.

Neil

Report · Mar 30, 2018

that's what I have but some of my documentaries are literally 4TB large when transcoded I need them on an HDD. Not paying 3,000 dollars for a 4TB SSD and I don't think they even make those.

Report · Mar 30, 2018

Yea, I know the feeling. For 4k work I often use 1/4 size Cineform proxies but still, it takes some space. Late projects you just have to get disc space for it all.

Neil

Report · Mar 31, 2018

So how come when I do the difference mode under blends it's just a black picture? Wouldn't that mean there is no degradation?

Report · Mar 31, 2018

now this isn't confusing. If I export out a .mts clip as high quality cineform and use difference under blend modes there is some degradation but not with .mp4 weird

Report · Mar 31, 2018

4TB large when transcoded I need them on an HDD.

New, 4TB and higher, Desktop Internal Hard Drives, Hard Drives, Components - Newegg.com

Report · Mar 31, 2018

that doesn't help me as I edit some projects on a laptop and I can't hitch up a regular internal drive

Report · Apr 01, 2018

bryced87 wrote
that's what I have but some of my documentaries are literally 4TB large when transcoded I need them on an HDD. Not paying 3,000 dollars for a 4TB SSD and I don't think they even make those.

Currently, it'd be a 4TB SSD RAID0 consisting of four 1TB SSDs. And yes, it'd be a small fortune.

Report · Mar 31, 2018

how many more times can I seriously keep exporting a .mp4 clip before degration occurs?

Once.

Whether or not you can see that degradation is a different question.

Report · Mar 31, 2018

so how come if I export a .mts clip as cineform high quality and put that clip one track above the .mts clip and choose blending mode difference there is visible pixels which shows degradtion but if I do the same thing with a .mp4 file there is nothing there? From what I can see cineform reduces the quality more than .mp4

Here is cineform high quality with difference blending mode turned on

Here is .mp4 from the .mts clip with much less degradation. I don't see any degradtion with the .mp4 file and both cineform and .mp4 came from the same .mts clip

Report · Mar 31, 2018

bitrates super high do increase generation copies. you can even have lossless mpeg4 if quantisizer is infinite. rc at 16 is good for probably 3 or more generations. these files are massive(close to 444 rgb uncompressed) and wavelet codecs listed above are gentler on visual artifacts. try cineform at level 5 to test. our eyes are more sensitive to luma than chroma, but if you export a 4:2:0 several times, you're quartering chroma each time you do it even if its not readily apparent. which means being able to greenscreen key stops after 1 generation, and being able to grade, after 2. also, any 2nd gen gamma color correction will not survive an 8 bit export, as talked about below. it's essentially 'burned in' permanently.

444 vs 422

Cineform

8 vs 10 bit

Cineform

Report · Mar 31, 2018

well, I think based on all the tests I did it just makes since for me to convert AVCHD to .mp4 and then when I export it for final use I'll export a quality 4 cineform file and then use that as my master to export other formats. Also from now on I'm going to just record in .mp4 since I can easily manage those files easier inside of windows 10. AVCHD won't let me add tags or anything to windows explorer but I can with .mp4 Then I'll just make proxy files using cineform 1 low quality as proxy files and then edit with those.

Report · Mar 31, 2018

i'd do some extreme grading tests before committing 100% to this workflow. particularly the highlights and shadows if you're not keeping original footage. zoom in 400% and make sure you're not cutting yourself off from future grading opportunity. having 1/8 color information is not something I would want personally, but maybe you can get away with it.

Report · Mar 31, 2018

what exactly are you talking about? filming in .mp4 should be not different than filming in AVCHD. I can color correct AVCHD fine it's just that I can't rename the .mts clips in the AVCHD card folder structure without ruining the clips.

Report · Mar 31, 2018

also if I film in .mp4 that is the original native media. Still confused what you mean by it will cut off 1/8 color.

Report · Mar 31, 2018

did you read the 444 to 422 cineform page I linked? h.264 and avchd are 4:2:0

you're losing:

½ horizontal resolution,

½ vertical resolution

for a grand total of 1/4th chroma left

capturing it once in camera plus transcoded from mts to h.264 is 1/4 + 1/4=1/8th of chroma information left.

Chroma subsampling - Wikipedia

Report · Mar 31, 2018

http://goughlui.com/2016/11/22/video-compression-x264-crf-generational-loss-testing/

Report · Mar 31, 2018

oh okay. Then how about just transcoding the avchd footage to cineform quality 3 for high quality? Also do I really need proxy files if I already have transcoded to cineform? If space is an issue I could buy another 1TB SSD and just split my files across more than one SSD since I generally only work a section of footage at a time when it comes to documentary filmmaking. I don't see why I would need a proxy file from an already transcoded high quality cineform file.

My issue is that regular HDD's externally via USB 3 don't playback well on a laptop but the SSD is fast.

If that won't work what about just in the future recording all my footage nativly in .mp4?

Report · Mar 31, 2018

Cineform 3 might be ok, 4 would be good for heavy grading.

You can set the playback to 1/16 and see if you even need a proxy.(probably won't)

Depending on the camera, either avchd or mp4 could have higher quality.

you'd have to test.

Report · Mar 31, 2018

both AVCHD and MP4 record at a max of 24mbps in 8 bit color. I did read in the manual that if I get an external recorder I can record 10 bit files using the SDI output on the camera but so far the only external recorders I can find record in DNXHR and Apple ProRes which seems overkill for the type of films I'm creating and I'm on a PC and I'm skeptical that Apple ProRes will continue to work in the future granted Apple is no longer updating QuickTime for Windows. I honestly use to edit on a Mac but no longer do that as the cost to make a PC was much cheaper and I can get more process power out of a PC than an iMac for half the price of what Apple sells their Macs for.

Report · Apr 01, 2018

bryced87 wrote
I'm skeptical that Apple ProRes will continue to work in the future granted Apple is no longer updating QuickTime for Windows.

Adobe has licensed Apple ProRes, so you'll still be able to play ProRes clips in Adobe Video & Audio applications even if QuickTime is not installed.

For what it's worth, ProRes was just adopted within the last month or two as part of the standard for delivering TV spots for broadcast and cable.

Although, it never hurts to be leary about CODECs. I have a library of Radius VideoVision clips and a handful of Large TrueVision clips that can't be played unless I boot up my PowerMac 8100 or Power Computing PowerTower Pro.