Don’t want to record and store 1.5 GB/sec.? You are not alone!
Not only does it take a huge amount of disk space, the components used in processing that data at those speeds are expensive. So data compression was develpoed in order to record a lot of data in a small space.
HDV compression is very efficient, using a long-GOP (group of pictures) to store high-definition images. However to edit that material, the B and P frames need to be decoded into I-frame only
in order to be edited. That does add a layer of compleximity since they have to be re-encoded if you want to go back to tape. For more about long-GOP, see
Final Cut Pro HDV
Computer editing companies are coming out with their own compression algorithms. Avid’s DNx and Apple’s ProRes both do the same thing: reduce the file size of HD material to around the size of uncompressed SD. Many of the camera manufacturer’s compression schemes did not use the full raster so both these new compressor’s use full 1920×1080 and can be 10 bit. By picking different frame rates, you can taylor the compression for your production. Less complicated image productions, like a talking head in a studio, can get by with more compression without seeing artifacts. Complicated images, like sports or fast moving images with fine detail, look better with less compression.
Panasonic is offering the new AVC-Intra. AVC is a compression method that Sony, Panasonic and others have agreed to for consumer cameras. If is a long-GOP method useful for recording but not great for editing. The “Intra” style is I-frame only so each frame stands alone and is recommended for high-quality production and editing. AVC-Intra
Most of these compression types start out with discrete cosine transform. MPEG
Compression is becoming almost invisible. Looking at the new Apple codec, I could not pick out any artifacts in their demo. It is about a 6:1 compression ratio which should give most everyone outstanding results. The Avid DNx also offers excellent quality.In fact, transcoding can be helpful if you don’t have the native codec used in the camera. You can take the RED camera 4k image file and transcode it to Apple ProRes for editing.
For editing, look for intra-frame compression. If you want to just record and playback, the long-GOP of HDV will serve you well.