HD workflow???

[Walter Soyka]

[Samuel Enblom] “I’m pretty sure that if you export from avid with h.264 codec and then import into AE with current settings and then exporting again with the same settings the quality loss should be so slightly you wouldn’t notice it since it wouldn’t have to re-compress that much info…”

That’s not entirely accurate.

When working with compressed video, AE (like all video processing applications) must first decompress the video into an uncompressed image buffer before it can render effects on it. When AE renders compressed video, it must start with an uncompressed image buffer because this is the only input a video codec can take.

Compressing an H.264 video from an H.264 source is somewhat like making an analog dub of tape — you lose a generation and incur quality loss because any artifacts or loss from the first record are piped into the input of the second record, and compounded by artifacting and loss there as well.

With extremely high-quality lossy compression (as with extremely high quality tape), you can reduce — but not eliminate — this loss.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Mata Hari]

Thanks for all your help guys, the project has turned out to be a disaster but I have learned a lot. However, having completed the piece I can conclude that exporting without quality loss requires lots and lots of practice.
As for the workflow itself I haven’t got any more experienced, although I can say that working on small pieces is a lot easier than working on 10 mins full HD within one composition unless you have a monster computer.

[Samuel Enblom]

I know the one who started this thread has finished his assingment but I just wanted to add a short comment/question.

I think what I was meaning was that if you in the first place, with your first editing software (lets say fcp or avid) export with current settings you won’t have to compress the video as much, and then if you compress it in AE the quality loss shouldn’t be as big.. Or am I wrong?

[Mata Hari]

Hi,
My initial question would have been in regards to workflow to save computing time and the endless rounds of exporting small bits, effecting small bits and so on. Let’s say you’re working on a full feature and there are 10 places in the movie that you want to work on. Someone suggested me to work on full res, but my computer was not strong enough to do so, so I guess it was my own fault to take on such a job using my own computer although I’m still in the dark in terms of workflow.

[Walter Soyka]

That’s what I was trying to explain. Working with uncompressed files is actually easier on a lower-powered computer than working with highly compressed files. With uncompressed files, the file size itself is large, and the data rate is high, but very little CPU power is required to play it back or open it for effects. With highly compressed files like H264, the file size is small, but he computer has to work very hard just to decompress it for further processing.

The best workflow is to work with uncompressed files, or lightly-compressed, intraframe codecs light ProRes or DNxHD. Even though the files are larger, they require substantially less CPU power for playback. By working with heavily compressed files, you are wasting computer resources on decompression when you could be using them for effects.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Walter Soyka]

After Effects, since it is bult to do image manipulation, always uses uncompressed frames for its internal rendering. AE thinks in uncompressed. To use any kind of compressed media, AE must decompress it into RAM for processing, then recompress it for output.

This is not unique to AE. Any time a frame of video needs to be modified, it must be decompressed for processing first. NLEs can only avoid recompression of media in certain specific situations.

H.264 uses inter-frame compression. That means that in order to reduce file size or data rate, not every frame stores complete information. Videos are broken down into a series of groups of pictures (called GOPs). These groups are made up of complete frames (called keyframes or I-frames) and incomplete frames (B- and P-frames). The incomplete frames refer back to common pixels of similar blocks from nearby frames. In order to compute a single incomplete frame, the computer may need to consider several frames, both complete and incomplete. This raises the computational power necessary for decode, and complicates cuts. If the cut takes place within a GOP and breaks the references sn incomplete frame relies on, that frame and any other similarly dependent frame must be recalculated. This means that even cuts from an inter-frame compressed clip may actually require a generation of decompression and recompression.

Codecs like uncompressed, ProRes, and DNxHD all use intra-frame compression, which means that every single frame is completely self-contained. An NLE can copy compressed frames for a cuts-only sequence, and computational requirements for decode are vastly lower.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Mata Hari]

Hi,
Thanks for your help, that information was unbelievably useful, just one more question for future reference. If I receive any highly compressed file to work with, would it make a difference in terms of computing time if I recode it with prores or DNxHD?

[Walter Soyka]

Yes. Transcoding should improve performance, especially on lower-powered computers. Using a high quality codec like ProRes or DNxHD will neither improve the quality of your compressed original nor degrade it noticeably. It is highly recommended to use intraframe compression for AE CS4 and earlier to avoid bizarre rendering glitches.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events