It is now common to shoot HD video and deliver it in standard definition frame size and rates. In these cases, the best practice is to work in post-production with the original HD format we shot on, then convert to the SD frame rates and size afterwards to retain as much image quality as possible. Compressor 3.5 and 4 do a very good job with the conversion. It is important to remember that we are always balancing between quality and speed. You can have all of one, but none of the other. Or you can have more of one and less of the other.
There are two ways we can create jobs in Compressor. If you’re working in FCP X, use the Share menu and chose Send To Compressor. If you already have a QuickTime file to transcode, launch Compressor, use the Job menu and go to Source, File, and then chose the file you want to transcode. Next, at the top of the Settings window (Command-3), type ProRes into the search field, and drag the Apple ProRes 422 preset onto your job in the jobs window above. In the job pane next to the icon of your QT file you see the transcode preset, ProRes 422. Click to select it and in the Target menu to go Destination and verify where you want the new file to be written. Finally if you want to customize the new file’s name, click in the name field and type in the name you desire.
With our ProRes preset still selected in the jobs window, go to the Inspector window. There is a row of six buttons across the top. Click the second from the left for the “Encoder” section. Next to Video and Audio you can click a Settings button to configure the Frame Rate. My example is 59.94 fps and I’ll change it to 24 fps here.
The next button to the left is the Frame Controls section. Here we set the quality and method by which frame size and rate changes will be handled. We don’t set the actual fps or frame dimensions here, only how changes to each are handled. We set fps in step 2 already and will set frame size later.
Click the gear icon to the right of “Frame Controls” to enable it, and change the drop-down menu to “On”. In the Resize filter menu set it to “Best (Statistical Prediction)” for best quality, although a longer transcode time. This analyzes the video frames on a per pixel basis to decide where each pixel will be in the new file’s frames.
The “Output Fields” I’ll leave as “Same as source”. If the original is progressive, we get progressive frames. If it’s interlaced, we get interlaced fields. To change from one to the other in the transcode, here is where you set it.
“Deinterlace” is only necessary if you're going from an interlaced source to a progressive transcode. The Fast, Better, Best settings go from low quality / fast encode, to a balance of the two, to a slow encode / best quality output. Leave “Adaptive Details” checked.
Below our Resizing Controls is our Retiming Controls section. Obviously we will set up how we want our frame rate conversion to be handled. Again we have a menu for “Rate Conversion” that balanced quality and speed. Select “Best” as it uses Optical Flow with a high quality of detail in the calculations of pixel vector paths. It is the best quality rate transcode, but the most time consuming option.
When retiming video that has audio tracks the audio will be automatically retimed to match the new video frame rate. Nothing will go out of sync. Pitch will also be corrected so that your new audio sounds just like the original.
“Set Duration To” I’ll leave at 100% for the same playback speed as the original.
Note: if you click the menu button to the right you’ll see a list of presets. Choosing one will conform original frames to the new rate, and NO new frames will be added, NO frames will be removed. it will simply keep all the original frames and retime them like Cinema Tools did for those familiar with it.
The second button from the right is the Geometry section. The first option I’ll set is “Dimensions”. I am going from HD to SD so I’ll set “Frame Size” to “720x480” and leave “Pixel Aspect” to “NTSC CCIR 601/DV”.
Since I don’t want to letter box my image I’ll go up and set “Crop to” for the “4x3 1.33:1” preset. The preview window will now show you the new frame on the right, the original on the left. If you want the original HD full frame letter boxed in the SD frame, leave all cropping parameters at zero.
Now we’re all set up. You can click the Save button at the bottom right of the Inspector window if you do this operation often and would like a fast access preset. Next, click the Submit button at the bottom right of the jobs window to start the transcode.
This article should give you a basic understanding of the necessary controls to do the highest quality transcode when changing frame sizes and rate.