Standard Definition Video Recording Formats
First of all, it should be noted that, without exception, all modern digital video cameras use certain compression algorithms and compression of the original video, and the “recording format” just characterizes the compression algorithms used. Let’s see what recording formats are found today in standard-resolution digital video cameras; we will talk about high-resolution video cameras separately, a little later.
DV is a video format with frame-by-frame compression (compression), that is, each frame of the video is compressed individually. At the same time, the compression ratio can be variable within the same frame — areas of the image that are difficult to compress are compressed with a lower compression ratio, and simple ones with a larger one. In this case, the total compression ratio for the entire frame remains constant (5: 1). The resulting stream for video is approximately 25 Mbps. The DV frame size is fixed and is (for the PAL standard) 720×576 pixels. This format is used in miniDV camcorders, and video recording, respectively, is performed on miniDV cassettes.
The advantages of this format are the best standard-definition video quality to date and the greatest, compared to other formats, ease of editing associated with minimal loss of video quality during “recompression” (compression – editing: applying effects, titles, transitions – re-compressing the video) .
MPEG-2 is a video format with the so-called inter-frame compression. When compressing video in this format, the so-called key frames are selected first – they are compressed in much the same way as they were done in the DV format. But key frames make up only a small part of all frames of the compressed video, and the remaining frames are compressed using a different algorithm. It is not the frame itself that is compressed, but the differences between the frames.
That is (and this is the most important difference between MPEG-2 from DV), the compression is not frame-by-frame, for most frames of a video sequence we do not have a compressed frame, but compressed information about the differences between this frame and the key and intermediate frames closest to it. At the same time, we can achieve a higher degree of compression with a quality comparable to DV.
But there is a downside – firstly, encoding / decoding in MPEG-2 requires large hardware resources, since the encoding process itself is much more complicated than encoding in DV. Secondly, when transcoding (for example, when editing a video recorded in MPEG-2), the quality of recompression will be greater than that of DV – again a consequence of a more complex encoding algorithm and a larger compression ratio. That is, MPEG-2 is less convenient for editing than DV. And finally, thirdly, MPEG-2 provides comparable to DV quality at a much higher compression ratio only for a relatively static picture. In this case, the changes from frame to frame are small, and MPEG-2 interframe compression works well. But in dynamic scenes where the change from frame to frame is large, the quality of MPEG2 inter-frame compression can be significantly inferior to the quality of DV frame-by-frame compression (you probably had to watch the “squares” on a poorly encoded DVD).
This format is used in DVD and HDD camcorders, as well as in standard definition flash camcorders. The frame size, as in the DV format, is 720×576 pixels (with the exception of Panasonic cameras, in which this size is 704×576 pixels).
High Definition Video Recording Formats
High-resolution video (hereinafter, HD-video, from the English. High Definition – high definition) confidently enters our lives. Its spread is facilitated by the increasing popularity of large-screen LCDs and plasma televisions, on which standard-definition video already looks “not very”. And if two years ago all domestic HD-video cameras were presented by one model – Sony HDR-HC1E, today all the major manufacturers of video cameras (Sony, Panasonic, Canon, JVC) release and are constantly expanding their line of HD-video cameras. But with all the variety of models, the lion’s share of the market for household video cameras is occupied only by two high-definition video formats: HDV and AVCHD, which we will now consider.
HDV is the HD video format that first entered the consumer market (it was in this format that the aforementioned Sony HC1 was shot). The developers of the HDV standard had the task, firstly, to significantly increase the resolution of the final video compared to standard-definition video, and secondly, to leave the video stream comparable to what we have in the DV format, this would make it possible to record HD video on the same miniDV cassettes, without sacrificing time for shooting on one cassette. To solve this problem, the developers of the HDV standard (which were Sony, Canon, JVC and Sharp) used the familiar MPEG-2 compression format. At the same time, the video stream remained the same as for DV – 25 Mbps. This was achieved, in addition to using a higher degree of compression, using anamorphic transformation.