does mpgeg1 need less amount of space than mpeg2

[bernd_b]

I've encoded the same movie of a lenghts of 42 minutes with the same settings:

CQ 100
min bitrate 300
max bitrate 2530

the same gop structure (kvcd template),
the same audio settings (48000 khz, 192kbit)

The first run I choosed mpeg 1 as output format (mpeg1 Video CD non-standard) and then mpeg2 (mpeg2 Super Video CD (VBR))

To my surprise the output size of the mpeg1 encoding is 740.198.648 bytes and the mpeg2 output ist 859.443.088.

So mpgeg 2 needs 15% more space for the same job?
Has anyone done similar experiences? I found nothing doing the search.

[Bubba]

bernd_b

VCD is 352x240/288 resolution which is smaller than SVCD (480x480/476) and thus will produce smaller output, if encode with the same rate. But if you change to an xVCD template such as 702x408, and encode with the same rate as you describe, then you will see that the Mpeg1 file will be bigger than the mpeg2 file.

[bernd_b]

I always used the same resolution D1/half: 352*576

So the resolution doesn't explain the file size

[Mug Funky]

that's an odd one... it might have something to do with quantization... did you check the quality? i'd imagine the mpeg-2 to look better.

[WarpEnterprises]

The Quality settings is by no means a measure for filesize.
It is definitly different between mpeg2 and mpeg1 (nonlinear vs. linear).
What should CQ 100 do? This should result in nearly CBR at 2530kbit.

Beyond that there is no real quality/size difference between mpeg1/2 (not that leap as e.g. MP2 vs. MP3). But MPEG2 has much more features (e.g. interlaced)

[bernd_b]

Maybe of interest:
meanwhile, I've done some furthter tests. The same settings as described above, again 352*576 resolution. I took a clip with advertisment and trailer of 3:12 minutes, which has a in my opinion good combination of high and low movement parts.

Here are the file sizes:

CQ__________mpgeg1___________mpeg2________Index
100_______55.255.424________64.809.388________117
95________54.985.840________63.647.388________116
90________54.785.976________58.478.812________107
85________54.641.888________54.095.748_________99
80________49.803.320________49.715.008________100
75________45.283.140________45.062.360________100
70________38.908.408________40.284.216________104
65________37.844.016________37.509.360_________99
60________33.704.972________35.152.824________104
55________30.277.072________31.706.332________105
50________27.588.204________29.052.324________105


Hope I did no mistakes. Comments welcome!!!

[joshyg2]

somebody correct me if im wrong, but CQ and VBR are two different methods of encoding.

CQ has no average bitrate constraint, so the encoder can use as much compression as it wants to without a average constraint, meaning you will never get exactly 795 mb.

Unlike VBR, whether it is MPEG1 or MPEG2 at any resolution, you have a min/avg/max the average is the same as the constant bitrate which is calculated by the length of the video and the desiered file size.

[WarpEnterprises]

Strictly speaking VBR and CBR describe the RESULT.
CQ (and all other modes resulting in VBR) describes a METHOD how to control VBR.

Don't mix it up with the name of the TMPG SETTINGS.

[EDIT]
+--- summed up perfectly by you.
|
v

[joshyg2]

true that. Sorry I got it mixed up - TMPG says its a 'rate control mode' which is true, although different control modes gives the user more control.

With CQ, its gives the encoder more control, in that its priority is Quality.

With 2pass VBR, its gives the user more control, in being able to get the average bitrate, thus being able to control the final file size.

The same goes for CBR, but it gives the encoder no freedom, to change the bitrate as it needs to. But again enabling the user to control the final file size.

[Kika]

To make it clear: CQ IS a VBR encoding Mode. Guess you mean 2pass VBR, but that's an other story.

MVBR aside, TMPGEnc provides 4 VBR-Modes:

CQ
CQ_VBR (automatic VBR)
2pass CQ
2pass CQ_VBR (automatic VBR)

[joshyg2]

sorry i meant 2pass VBR

[ronnylov]

But can mpeg1 be encoded with VBR according to it's specifications? I thougt mpeg1 was CBR only, at least on VCD and maybe DVD too?

[Kika]

You can use VBR on MPEG1, but in that case, you are leaving the Standards. Most Players will accept such Videos, but some do not.

[Mug Funky]

hmm. that still doesn't explain the different file sizes if both mpeg1 and 2 were using CQ.

i think it must be down to the nonlinear Quant scale preserving more details. it'd be interesting to do PSNR tests between the 2 encodes. (esp. on interlaced video where mpeg2 would win easily)

[Kika]

MPEG1 and 2 are using different Quantizer Scales. Linear on MPEG1, Non-Linear on MPEG2.

It's not easy to explain, and my english isn't good enough to do that, but have a look on bernd_b's Table, it say's a lot.

Zhe second difference ist the DC Component precision, MPEG1 always uses 8 Bit, whil Standard for MPEG2 is 9 or 10 Bit. That will give you a better Color-Quality, but need's more Bitrate.