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Bizzare quality issue on export of one section of a sequence from premiere in to h264 MPEG4
I have a completed, rendered sequence ready for export. It’s destined for the web and I compressed to a 1920×1080 h264 file in mp4 container. I selected a variable bit rate of average 8Mbit with a maximum of 12Mbit. Out of desperation I even bumped that up to 9 Mbit and checked the render at maximum depth and maximum render quality.
My issue is that everything exports just fine except one short section of the sequence, the same place every time. I suspected it may be something to do with render files but I have Use Previews unchecked. The section of sequence in question flips abruptly from acceptable, desired quality to a very pixelated very shoddy quality over the space of roughly 1-2 seconds before returning (in the same frame and cut) to a normal, acceptable level. The section of timeline involves a background jpeg file, and one animation mov with transparency. The video is of two figures (stills) standing over the top of the background jpeg image, whilst falling money falls past the camera and in front of the figures. During the low quality section of exported video, the money remains crisp, yet the figures, and the background have this dramatic drop in quality to something resembling a very low resolution and low bitrate file. The weirdest thing is that the figures and the falling money are one asset, they are a single quicktime, animation codec file exported from after effects, that seems particularly strange to me because I simply can’t figure out how media encoder seems to have so successfully isolated those two elements of the same video file to make one of them look like crap and the other look just fine, I also don’t understand why it doesn’t last for any logical duration corresponding to the position of clips in the timeline or events on screen. The return to normal quality happens midway through the clip of the falling money so it’s not like it lasts for the duration of the falling money clip.
Anyone know how to fix this? I suppose I could try a constant bit rate or a higher bit rate, or both but I want the best bang for my buck in terms of file size hence the choice of 2-pass VBR to begin with.
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2 Replies
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You can do a “manual override” of that section of video. Export JUST that area using a high quality intermediate codec, such as the Animation codec you mentioned. Export as “Video only”. Import the resulting short clip and place on higher track above original clips. Export entire sequence to desired output codec.
So basically, you are doing a pre-render of that segment to avoid whatever weird thing is happening. If the short render clip looks fine, then it ought to also export fine in the final video.
Sometimes there is no rhyme or reason as to why these things happen. Some folks will tell you to turn off GPU acceleration, maybe there is something not quite right with the source files in that area of the timeline, who knows?
Thanks
Jeff Pulera
Safe Harbor Computers -
VBR encoding with lots of money flying in the frame will create exported frames that are all at different compression rates and potentially different quality.
David Roth Weiss
Director/Editor/Colorist
David Weiss ProductionsDavid is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro forum.
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