Oversized Files - Why and what can I do about it?

[Locutus]

Hi everybody!

First of all:
Thanks to all the moderators of doom9 for their great work!

I want to encode a DV type 2 file with VirtualDub (2-pass encoding, DivX Pro 5.0.2). The source file is 1h 2min 30sec long and GordianKnot tells me to encode it with 1426 kBit/s (700Mb CD, 56Mb mp3 audio file). The resulting DivX file without audio is 747Mb big!

Why doesn't DivX keep the Bitrate? Is it a general bug? How should I calculate the bitrate?

Thanks for your help!

Locutus

[DJ Bobo]

This is impossible! I never (and I really mean never) got an oversized file using DivX5.
A possible cause of your problem may be you having set the max quantizer a way too low. You shouldn't go under 8.

[Locutus]

Well, i have encoded several DVD into DivX now and sometimes i had an oversize like 1 or 2Mb, which was probably due to wrong Bitrate calculations. Nevertheless, except for this file i never had one that was about 100Mb larger than expected!

I also did not change the standard settings of the codec, except for Bitrate. Could it maybe because the DV i tried to encode is interlaced? Do you get the same Bitrate calculations from Gordian Knot? Maybe that's the error, although i can't imagine as GK has always worked perfectly for me.

Thanks in advance.

Locutus

[DJ Bobo]

An oversize of 1 or 2MB is no oversize ;)

The bitrate calculated by GKnot is right.
I don't see any other explanation than the matter with the max quantizer ...

You deinterlaced your video right?

[Locutus]

Thanks so far.

Nope, I didn't deinterlace the video. I coded it right away after recording it from my DV Cam. I was aiming an unfiltered version for later processing and cutting. Should i deinterlace nevertheless?

Thanks.

Locutus

[DJ Bobo]

Of course! DivX encodes in progressive mode ONLY! if you want to process later, encode to interlaced MPEG2 (with a rather high bitrate). When you encode to DivX and leave it interlaced, you won't be able to process it correctly later since all interlacing informations are gone.

You can consider it as an absolute rule: have interlaced source & wanna encode to DivX? deinterlace it first, no matter what!

[drizztcanrender]

Yeah interlaced content needs a lot more bits from the codec,thus the increase...

[Locutus]

Yes, that makes sense and is pretty interesting. So, as far as I know interlaced video means that there are A and B frames taken at slightly different time stamps but played at the same time nevertheless. This results in the stripe like picture when there is motion in the movie. So, if that's right then I understand your point and why the compression of an interlaced video does not work with DivX.

But what does a deinterlace filter do to my video. How does it combine the A and B frames to one? Does deinterlacing result in loosing quality?

Thanks.

Locutus

[jggimi]

There are several methods used to de-interlace. Here are two of the the most common:

1. Cut the resolution in half, then resize. Gordian Knot calls this "fast deinterlacing" and uses VerticalReduceBy2 in .avs scripts when this method is selected.

2. Use a process which analyzes pixels, de-interlacing what the software determines are interlace artifacts. Donald Grafts DeComb will do this in .avs scripts, either during a Telecide command, or via the FieldDeinterlace command. GreedyHMA is another process that does the same sort of thing, using a different algorithm, called appropriately, Greedy/HM.

Choose what looks best to your eyes. I find that the choice is often content specific.

[DJ Bobo]

If you want optimal quality, you'll have to make interlaced MPEG-2 out of it (SuperVCD or preferably eXtended SuperVCD) and watch it on TV.

You wanna deinterlace and make DivX? you'll certainly loose quality.
Way1: discard one of the fields (works well only on regular PAL or NTSC interlaced video)
Way2: use the Decomb plugin for AviSynth and use the command: fielddeinterlace(blend=false) <- fields are interpolated but no interlacing lines anymore (this way delivers the best quality! works also well only on regular PAL or NTSC video)
Way3: bob to 50fps if PAL or 59,94fps if NTSC <- best motion: fields are shown one after another as on TV (you can use it with any type of interlaced video, but especially on non-standard telecined NTSC video and PAL video converted from NTSC in a weird way)
Way4: fielddeinterlace() (blends both fields together) which is used on PAL video that was converted non properly from NTSC (and vice-versa) as an alternative to bob (has better image quality than bob, but worse motion)
Way5: IVTC on NTSC video only which was originally shot on 24fps FILM (99% of hollywood movies and 95% of Anime). This filter reconstructs the original 24fps and gets rid of the repeated 6 remaining frames per second. [This method doesn't decrease quality at all!]
Way6: Telecide() (part of the decomb plugin for avisynth) used especially on PAL movies and Anime which was speeded up to 25fps but was non correctly diffused, or encoded interlaced with fields in the wrong order. This filter recombines the fields in the right order. [This method doesn't decrease quality at all!]

... oh .. jggimi was faster ..

[jggimi]

Yes, but, as usual, with much less information. :-)

[Locutus]

Thanks to everybody for the comprehensive information.

Before reading your posts i tried to encode the DV to DivX again. This time using Virtual Dubs deinterlacing filter (Blend fields together). Now fortunately it works. Thanks that's the sucess i needed. Now i'll try some other deinterlacing filters u suggested.

Maybe i'll also use MPEG2 then instead of DivX.....we'll see...


Thanks

Locutus

[Locutus]

...there is one thing i didn't understand. I know VCD, SVCD (which is MPEG2), but:

What is "eXtended SuperVCD"? And what is the difference between SVCD and extended SVCD? Can a DVD player that plays SVCD also play extended SVCD?

Thanks.

Locutus

[jggimi]

All of those questions can be answered at www.vcdhelp.com, where you will find descriptions of every possible Video CD format, and a large database of standalone DVD players and what kinds of physical media they accept, and what kinds of Video CD they can do.