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Mpeg compression and interlacing
Ok I am really trying to get a clear understanding about the concepts of video compression (i.e. interlacing vs deinterlacing, Variable and Constant bit rate, field dominance and any other confusing settings that go along with compression).
My problem is that when I create a new project with the sequence settings for NTSC DV footage and import an mpg clip to the timeline, edit it and then export using Adobe Media Encoder with the MPEG2 preset, the resulting footage plays with very visible scanlines. I know from previous posts not to check the deinterlace option as it will result in a loss of half of the video’s original quality. The field dominance is set to lower which i thought was right.
Can anyone enlighten me into this crazy world of video compression and its many options and concepts?
Chad Mayeux
Metter, GA
Pineland Technology Solutions
Videographer/ Digital Artist -
5 Replies
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Let’s start with where you are viewing the footage.
On computers, which always use progressive displays, you will usually see the interlacing lines. That’s normal. Players such as VLC, even the latest windows media player allow you to minimize the effects with various de-interlacing settings, but again, your picture may look softer as a result.
If you are going to the web, you probably can and should de-interlace since the resolution of your export is almost always lower anyway.
If you are viewing the footage on LCD/ plasma tv, or projector, the lines won’t be seen because they have built in de-interlacing.
Regarding the rates. A standard single layer DVD with a length of 1 hour or less can usually be burned a 7.5 MB/s CBR (anything higher usually requires high end DVD media and burner or you may see skipping).
You can use CBR in that case because there is enough room on the disc to allow for a maximum constant bit rate.
For anything over that, you would use VBR 2 pass. The first pass will analyze the scenes for variable degrees of motion, and the second pass will encode, adjusting the bit rate accordingly; high motion scenes require a higher bit rate because the entire frame often changes at every frame.
For VBR, you should use a bit rate calculator to manually fill in the settings.
Here’s one: https://dvd-hq.info/bitrate_calculator.php
Or you could let Encore automatically do the encoding for you.
Vince Becquiot
Director | EditorKaptis Studios
San Francisco – Bay Area -
That is such valuable information, thank you so much! Does anyone know of anywhere that has an article or maybe video lesson explaining the main concepts of video compression? I really would like to understand this process and what things like M-frames and B-frames and GOP are. Again thanks for the help so far!
Chad Mayeux
Metter, GA
Pineland Technology Solutions
Videographer/ Digital Artist -
[Vince Becquiot] “Or you could let Encore automatically do the encoding for you.”
Encore probably is the best bet, but from what I have learned in this industry it is also best to use a manual setting over an automatic (i.e. manual vs auto focus on a video camera). What I am thinking is that me understanding some concepts of compression and applying manual settings to the compressor will give me better results than hoping Encore gets it right for me. In the same sense I get better video when I control the focus manually rather than letting the camera decide what is best.
So my new question; are those previously mentioned assumptions correct? Is Encore good enough or is it worth understanding the compression process? (I compress something almost everyday)
Chad Mayeux
Metter, GA
Pineland Technology Solutions
Videographer/ Digital Artist -
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Just a quick comment about your interlacing problem. You may want to check out DVFilm maker. It will deinterlace your footage with a minimum loss of resolution. You can try the demo to see if it meets your standards.
Hope this is helpful,
Dave Keslick
dvfilm.comDave Keslick
DVFilm.com
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