MPEG format

Jun 02nd, 2010 by dvdxplayer 3,153 views |4 Comments

History. Approximately a decade old, yet newer than AVI, the MPEG format was an attempt to provide high quality video using smaller file sizes, as invented by the Moving Pictures Expert Group. The MPEG format has seen several variations over the years, having been one of the first streaming formats using SGI WebForce MediaBase (which failed), becoming the MPEG-1 VCD specification, moving to the digital satellite DBS/DVB/DVB-II MPEG-2 formats, becoming the de facto DVD MPEG-2 format, using the popular MPEG-Layer III (MP3) audio format, and most recently as the MPEG-4 DivX video format for video swapping online.

Editing. MPEG is a final product video format. After a video has been converted to MPEG, it usually should not be edited, especially ones that follow the full I-P-B compression scheme. There are actually several professional MPEG editing formats, though they use low or no inter-frame compression. For example, an MPEG-2 with I-frames only with CBR encoding, which is almost the same as an MJPEG.

Compression method. JPEG, MJPEG and MPEG are similar, but please do not confuse them. A JPEG image file groups similar information in the image, and squeezes it into the same space, compressing the file size (for example, in layman’s terms, instead of writing “BLUE” 81 times in a row, the compression scheme writes “BLUEx81″). A Motion JPEG, known as MJPEG, does the same, at a frame-by-frame level, essentially a back-to-back series of JPEG images. Each frame is analyzed for similarities, compressed, then the process is started over at the next frame (intra-frame compression). MPEG does this, as well as incorporates temporal compression using groups of pictures (the GOP, made of I, P and B pictures). Information is not only compressed in the frame (intra-frame), but between frames as well (inter-frame, I-P-B).

D-Values. Various resolutions are often referred to as D-values. Full D1 video is 720×480. Cropped D1 is 704×480. Half D1 video is 352×480. Quarter D1 (actually SIF) video is 352×240. Two-Thirds D1 video is 480×480. DVB and DVD-VR use unusual MPEG resolutions, sometimes called Three-Fourths D1 at 544×480.

MPEG formats. MPEG-1 is the oldest version of MPEG. MPEG-2 is the updated version of MPEG-1, introducing interlacing, and giving control over more advanced features of the format. DVD-Video uses MPEG-1 and MPEG-2. CD based formats, such as VCD and SVCD/CVD, use either MPEG-1 or MPEG-2 depending on the specs. MPEG-4 is the name given to newer AVIi codecs such as XVID, and is really not the same. See the charts on the UNDERSTANDING YOUR SOURCE guide for detailed information on the varying disc formats (DVD, VCD, SVCD, etc).

File extensions. The following file extension are associated with MPEG files:
MPG = .3 extension version of MPEG, from DOS/Win16 era, still used Win32/NT
MPEG = MPEG video, audio or muxed video-audio file
MPA = MPEG Layer II audio
MPV = MPEG1 or MPEG2 video
VOB = MPEG1/2 with DVD navigation data
DAT = MPEG1 with VCD navigation data
M1V = MPEG1 video
M2V = MPEG2 video
MP2 = MPEG Layer II audio. If it contains video, it is misnamed (ATI MMC did this in the old days)
MP3 = MPEG Layer III audio, not muxed with MPEG video
MP4 = MPEG-4 video file (should be in an AVI), misnamed

AVI captures are better quality? Assuming good capture hardware/software is being used, whether the video is compressed now or later makes no difference. This situation reminds me of the Bugs Bunny cartoon where Daffy asks Elmer, “Would you like to shoot me now, or wait until you get home?” Seriously, there is no difference. Daffy was somehow fooled into believing one was better than the other, yet the outcome was the same. He had his bill blown off.

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