Image quality loss at the beginning of my 1 hour project

[Juan23136567v7ml]

Hello,

I have a problem when exporting my project, which is almost 1 hour long.

Right in the initial seconds, when the titles start, the image loses quality, as if the bitrate is very low.
However, if I do the test and export just the first 15 minutes of the project, for example, the image quality is perfect from start to finish.

I work with 4 sequences: 3 separate sequences that correspond to 3 chapters in my project, formed by their corresponding clips; and a final sequence which is the final project, so that the timeline of the final project sequence includes an intro clip with the titles, + each of the previous 3 full sequences, and a clip with the final titles.

I use Adobe Premiere Pro 2022, and my video export settings are as follows:

Format: H.264
1920x1080px
Frame rate: 29.97
Speed ​​encoding: VBR, 2 pass
Destination speed: 20 Mbps
Maximum speed: 40 Mbps

I have tried different configurations and I cannot solve the problem: as I say, when I export the complete 1 hour project, the initial images are reduced in quality, appearing as pixelated.

What can be happening?

Thank you very much for the help.

[gerikp]

What about exporting out as a ProRes 422 MOV file and get a good export that is lossless as a Master File export and then making your compressed h264 from that file? This is my normal workflow. And lately, I have been noticing that same problem you are having with h264 exports. But it went away when I switched to Constant Bit Rate and not use Variable Bit Rate.

[Juan23136567v7ml]

Thanks for you answer.

I did it and got a 55 gb .mov master. The problem of image quality loss at the beginning of the video was solved, but now the .mov video has excessive contrast and color saturation, compared to the original clips and also to my initial .mp4 export. 

Any suggestion?

[gerikp]

How did you check the color of your file? The best way is to import your file back into Premiere Pro and double-check it that way because it could be the particular app you are using isn't showing you the exact color. It also could be that you have some color management settings applied in your export settings by accident.

[Juan23136567v7ml]

Thnx for the answer. I tried to re-export the my ProRes 55 gb .mov master, now to H.264, and the color and saturation problem was solved, BUT, again, the resulting .mp4 file shows this image quality loss at the beginning. I think it's a problem of premiere H.264 encoder, which in some way doesn't works well with my large project. 

Then, I tried to export in DNx MXF format. I tried various settings: DNx RGB 444 1080p 29.97 (10-bit), DNx HQX 1080p 29.97 (10-bit), and DNx HQ 1080p 29.97 (8-bit).
With the first one I had the same problem of different contrast and saturation than the original project. The same with the second format, although the differences of contrast and saturation were less pronounced. Finally, exporting in DNx HQ 1080p 29.97 (8-bit) format, I obtained an 87 GB master with, now, the same contrast and saturation as the original project. I guess it's because these settings are the most similar to my original clips.

Now I'll try to export this 87 gb master in a smaller .mp4 file size, but I guess that I will have the same problem of pixelated frames at the beggining of the video, due to the long duration of the project. I'll try exporting in CBR instead of VBR and see what happens, but I thought that exporting in CBR gives a worse quality than VBR, isn't it?

[gerikp]

Yes, please try an export using CBR it's what's we've been suggesting. CBR gives higher quality but also a higher file size. VBR helps lower the size because it lowers the bitrate depending on the level of detail needed during portions of the video. My guess is that there's something going on in your video that is tricking the VBR encode to think that it needs a lower bit rate and thus you get a lower quality portion of your video.

[Juan23136567v7ml]

Effectively. I exported using CBR (20 Mbps bitrate) and the problem disappeared: there are no more pixelated images at the beginning of my video. As you suggest, it seems that the encoding in VBR detects that the initial sequences of the video (which correspond to the initial titles and the beginning of the first frames) need a lower bitrate, and this is where the defective image occurs.

As I said, when exporting to CBR the beginning of the video looks excellent, BUT now I have the problem that there are certain moments in the video, especially during panning movements of the camera (which, in fact, aren't so fast), in which the image loses quality, as if in that moment you will need a higher maximum bitrate. This is the problem I encounter when exporting in CBR.

Eventually, I haven't been able to export my project in .h264 VBR with acceptable quality. What I don't understand is why if I export only a short initial fragment of the video in VBR, the beginning with the titles shows good quality. Quality loss on VCR occurs only when I export the full 1h long video.

I think the only solution is to re-encode my DNx HQ master with another program like HandBrake to get a reduced .mp4 file (about 8gb) with acceptable quality for me.

[Averdahl]

What can be happening?

By @Juan23136567v7ml

Use CBR instead of VBR when encoding.