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O
Offbeat Bryce Productions
Inspiring
March 30, 2018
Question

How many generations of .mp4 till quality degrades?

  • March 30, 2018
  • 2 replies
  • 4007 views

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?

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2 replies

E
excited_Genie16B8
Legend
March 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.

    O
    Offbeat Bryce ProductionsAuthor
    Inspiring
    March 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

    chrisw44157881
    chrisw44157881
    Inspiring
    March 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.


    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

    R Neil Haugen
    R Neil Haugen
    Legend
    March 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

    Everyone's mileage always varies ...
    O
    Offbeat Bryce ProductionsAuthor
    Inspiring
    March 31, 2018

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

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