What's the maximum sensible bit rate for 352x288x25fps MPEG-1 files?

[ajmoss]

I asked about this on the SVCD forum, and was advised that the video capture forum would be more appropriate.

There are several different types of limitation inherent in the MPEG-1 file format. For instance, the false colour halo around superimposed subtitles is completely unavoidable, but the pixellation in VCDs arises because the video bit rate is too low.

What I need to know is, if I'm storing half-resolution PAL recordings (352x288 pixels at 25 fps) as MPEG-1 files, at what video bit rate will I get the best results? I'd get a significant improvement if I increase the bit rate from 1.1 Mbit/s to 1.5 Mbit/s; at what video bit rate, X, will I get no discernable improvement to the picture quality if I were to increase it to X+delta_X ?

One of the FAQs on the www.doom9.net site states the typical compression ratio of MPEG-1 frames:

I-frame 7:1
P-frame 20:1
B-frame 50:1

This gives an *average* recommended video bit rate of:

352 x 288 pixels x 25 fps x 16 bpp
x ( 1/7 x 1/12 <- I-frame
+ 1/20 x 3/12 <- P-frame
+ 1/50 x 8/12 ) <- B-frame

= 1,530,000 bits/s

But I have no idea of the variance of these compression ratios; I need to know the video bit rate I'd need to store a much more complicated moving image.

Anyone advocating capture with a lossless codec is of no help to me right now; the cost per gigabyte of storage space makes long-term storage of Huffy-encoded video files completely impractical.

[Ookami]

IMO, this is one of the questions that no one can answer for you. You've asked "what is best?", well, it depends on YOU and no one else! The only real solution is to try a few captures with different settings (you should also fiddle with the other settings, like resolution etc.) and see for yourself.

There are some people that make a disgusting face when you even mention MPEG 1 at "near VCD bitrate and resolutions". And there are people who are even happy with lower settings than the original VCD ones. It is really relative. So there is no after the bitrate x you get no improvent, because "improvement" is relative.

Of course, you are right that there is a point when a higher bitrate is not of much gain, but that, again, depends on who you ask.

For example, when I use(d ;) ) Divx ;-) I almost never go over the bitrate of 2360 (the famous "Genesis" bitrate ;) ), altough higher bitrates sometimes helped, in most of the cases this is enough for me (<- don't forget that "me" :-) ). Well, altough know it's almost stupid to use the plain old non-SBC Divx ;-) ...

Also, you didn't mentioned if you will use you're captured files as the end files without reencoding. You can also use some filters and similar on the playback (Sasami2k player) to "improve" the quality while viewing.

BTW, Huffyuv is not the only codec for capture. You can use MJPEG, Xvid, one of the Divx codecs, MPEG2 and so on...

Sorry, for this long posting without real help, but in my opinion some questions need to be answered by the person who asks (whoa, what a sentence!) :) .

Waiting for the other replies,

Mijo "well, the next time he could just spare me from his soapbox" Rebic.

[Scuba]

When I am encoding with TmpgEnc I normaly set the bit rate to 3500Mbit/sec with Max of 5500Mbit/Sec if you are doing 2Pass VBR.
Try to do somthing betwin 3000Mbit to 5000Mbit.

Some CD-Roms will not play over 4500Mit nice so you might want to take it into consideration.

[ajmoss]

Originally posted by Scuba
When I am encoding with TmpgEnc I normaly set the bit rate to 3500Mbit/sec with Max of 5500Mbit/Sec if you are doing 2Pass VBR.
Try to do somthing betwin 3000Mbit to 5000Mbit.

Some CD-Roms will not play over 4500Mit nice so you might want to take it into consideration.

Are those numbers 1000 times too high?

[movmasty]

yes, 1000 times too high,
scuba, those are settings for mpeg2-SVCD,ajmoss was asking for mpg1-VCD format.

below i will use megabit=1,000,000bits, b=bit,B=byte

what is best?, well, it depends from....movie format specs....
those values for frames compression(that are not from doom but from a newbie user)are quite wrong, a more realistic value would be 1/12,1/24,1/48, but you cant really do nothing starting from there.
know that mpg1 standard for VCD(aka white book) is 1151kbps(140kB w/o audio),
what to say about it? that it gives a satisfactory quality for good,not noised images.
Know also that encoding a cif stream(352x288/240 x25/30fps) at constant Quantizer 2(max possible quality) you should get an AVERAGE rate of 2146kbps(262kB),
so you could stay among these 2 like begin,
2146b is a very high rate, if you use it at constant rate, low motion frames will have dummy bytes.
An old reference encoder like xing supported 1850kb like max for cif,
other standard values found in encode profiles are 1500kbps(183kB)and 1640kbps(200kB).

concluding,1151 is good(you could also go below,another common standard is 1098kbps) if you go for quality or the movie is noised,use 1500,if very noised 1640.

but when noise is present i advice you to use some smooth filter.


* Before Newton we had God, now God or math, our choice *

[movmasty]

a bitmap at 352x288 is 304128 bytes
a good value for an I frame in a mpg1 stream could be 20k,this is 1:15
a good value for a P frame in a mpg1 stream could be 12k,this is 1:25
a good value for a B frame in a mpg1 stream could be 7.5k this is 1:40

note that the max rate giving you sensible improvements depends heavily from movie quality,
noise takes many bytes to encode,
a very noised video encoded at Q3("max" perceptible quality imo)
can go over 300kB/s.

850kbs-min acceptable quality
1098kbs-a standard bitrate
1151kbs-"White book" VCD rate
1500kbs-a quality standard
1640kbs-200kB point
1845kbs-xing mpg encoder supported this value as max for cif
2146kbs-constant rate extrapolation from average encoding at minimum compression
2500kbs-average of noised movies at max visual quality can get here
4500kbs-very fast parts at min compression hit here
6000kbs-very fast very noised parts at max visual quality could go here
11000kbs-very fast very noised parts at min compression w/o B frames get also here
*(for "max visual quality" i mean Quantizer 3,for "minimum compression Q 2)

if you use mpg1 like capture,intermediate,file go as high as possible,
mpg is easy to edit too, but you should use an I-P only structure(no B frames,also very faster)
I-only structure is like motion jpg,fast,good quality,very easy to edit,but also relatively high size.
mjpg gives around 1300kB at 100% and 600kB at 95% encoding cif.

Another good format to store high quality movies is avi-indeo5,
check "quick compress" quality 100-95, keyframes 1-5.
it is one of the fastest codec,and gives less size than mjpg with good quality.

Divx4 at min compression and fastest motion compensation can be praticable too.

note also that you could capture with a lossless codec,
do some editing,very useful to cut un-necessary parts for long term storage,
then store in high quality mpg1,I-P frames only, at 200/250kBs,or high q divx 110/130kBs,max kframe to 2 and high scene change detection.