Ivan Myles
Forum Replies Created
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Thank you for posting the screen shot. Your export settings don’t match the sequence settings:
Aspect Ratio: Square Pixels (1.0)
Field Type: Progressive
Frame Rate: 30.00 FPS (although 29.97 will work) -
Can you specify 25fps when exporting from Compressor? Otherwise, transcode to ProRes using the native frame rates (20fps, 30fps), then adjust while editing.
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Was the aspect ratio set to square pixels? It would be helpful if you could post screen shots of your sequence settings and export settings.
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[Kevin Duffey] “So I should be safe if/when I can record with a BM Pocket Camera or Cinema Camera that records in DNxHD right?
“I will have to do some extensive testing. Send over your cameras and I’ll take a look. 🙂
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[Matt Campbell] “With DSLR and others shooing H.264 @ 420 color space, how is that better than transcoding to ProRes @ 422. I know you can’t add in quality if its only 420 to start, but don’t you at least gain more head room for correction and grading?”
Provided there are no issues interpreting the color data of the source file as described above, the disadvantage of transcoding from H.264 to ProRes or DNxHD is the time and disk space required to create the files. There is potential for generational losses from an extra encode cycle, but the impact should not be significant.
I’m not sure what you mean by headroom in this context. Effects will be processed the same regardless of whether the footage is H.264 or a ProRes/DNxHD copy of the original 4:2:0 data. If you plan to export an edited file for external color correction, then 4:2:2 and 4:4:4 exports are preferred over 4:2:0.
[Matt Campbell] “Also, when importing footage into Premiere, can you control how it interprets the footage. Is there any preferences or settings similar to how Avid MC does. You can select RGB, or 601 SD/709 HD and computer RGB. I know with FCP, you could not do this, everything was 601 or 709.”
601, half dozen of the other. 🙂
I am not aware of this functionality; hopefully other posters will respond. FWIW, Interpret Footage does not include it.
[Matt Campbell] “And with that, why would you want Premiere to upRez everything to 444 RGB? Why is this a good thing if your going to broadcast with 709 422 (YCbCr, or whatever it is).”
Premiere works in both YCC and RGB, but the differences are negligible at 32bpc. 4:4:4 is better for internal processing because interpolation issues will be minimized when effects are applied to the clips.
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DNxHD supports 4:4:4 (fully sampled) and 4:2:2 (chroma sub-sampled). The issue with truncating data above 100 IRE relates to color range and not chroma sampling.
This white paper provides more information on DNxHD. I found this post discussing 4:2:2 vs 4:2:0 encoding. In summary, the difference is more important for interlaced video.
Ultimate video quality depends on many factors beyond color space (hardware capability, calibration, file compression, etc).
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[Kevin Duffey] “First, how do you preserve this if you still want to transcode (and adding to that.. if you did edit the source, but then export to DNxHD at the end, I assume you’ll still lose the detail so how do you preserve it there)?”
Source footage should be checked using the YC and RGB Parade scopes. Note the vertical bars on the right side of each chart in the images above. These bars show the full range of values in each frame. If the range extends beyond 0-100 IRE, color correction effects such as Fast Color Corrector or Luma Corrector can be used to bring the clips within 0-100 IRE. Even if the Y-channel is within range, an individual RGB channel might be out of range. Further reduce luma until every RGB channel lies within 0-100 IRE.
[Kevin Duffey] “Second, cameras like BM and my Shuttle 2 record in DNxHD directly. Do they lose the detail from the start, or is it only the transcoding process that does this? Again I can’t imagine why the format would continue to be used and popular if it’s causing the loss of detail.”
The problem relates to how the software interprets the color space information in the source footage. In general, 8-bit Y’CbCr color using 220 increments (i.e. 16-235) should be displayed as 0-100 IRE. Sometimes YCC footage appears in Premiere Pro as -7.5 to 109 IRE. I’m not sure if this footage was actually recorded using 256 increments and then incorrectly overblown by Premiere Pro, or if there is a different root cause. Either way, it’s important to use the scopes and check for issues prior to encoding or transcoding.
[Kevin Duffey] “Seems wrong that transcoding a lesser (in my opinion) format like h264 would lose detail when going to an intermediate editing format like DNxHD.”
The problem is based on color range (16-235 vs 0-255); the primary difference between DNxHD and typical H.264 implementations is compression. An all I-frame H.264 with minimal compression is essentially a 4:2:0 version of an 8-bit DNxHD. H.264 specs include 4:2:2, 4:4:4 and 10-bit profiles, but most implementations do not support these variants (hence the popularity of ProRes and DNxHD as intermediate codecs).
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Vimeo supports 30fps. You might try converting the 20fps to 30fps using frame blending and leave the 30fps unchanged. Frame blending overlays two frames to interpolate an intermediate frame. Your existing frame sequence ABCDEF… at 20fps would become AB(B+C)CD(D+E)EF(F+G)… at 30fps.
If you go with 25fps, the best method would be to repeat every fourth frame of the 20fps video (ABCDDEFGHHIJKLL…) and drop every sixth frame of the 30fps video (ABCDEGHIJKMNOPQ…).
Another option would be to reshoot the footage.
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Please list your compression settings or upload a screen shot of the export panel.
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Spec details will vary. This post includes a link to Comcast ad requirements, if that helps.