Maximum SVCD video bit rate: 2600, 2520 or 2376 kbps ?

[cosmin]

Hi,

I couldn't find an official SVCD spec on the net, so I cannot clear up my confusion: what is the true maximum SVCD video bit rate allowed?

- Claim #1: The dvdrhelp.com site says it's 2600 kbps for *video only*, and 2778 kbps for video+audio *combined*.
- Claim #2: The VCDImager help says it's 2600 kbps for video+audio *combined*.

TMPGEnc uses 2520 kbps by default, and I believe this comes from 2778-256=2522, so it agrees with Claim #1.

The MPEG exporter from Adobe Premiere 6.5 forbids any *combined* bit rate above 2646 kbps, and uses a default 2376 kbps for *video only* (actually, this one makes sense, because 2600-224=2376), so it "sort of" agrees with Claim #2.

Besides this, the pcphotovideo site http://www.pcphotovideo.com/newpage21.htm claims that some SVCD authoring tools disallow a *combined* bit rate above 2600. Therefore, in spite that the spec says that 2600 is for *video only*, they recommend to keep the video bit rate around 2300.

So who is right, after all??

I am also curious about the maximum bit rate of the CVD: is it the same as SVCD?

[SatStorm]

Claim 1 is the correct one
CVD use the same bitrates as SVCD.

[disturbed1]

2778 is the total muxed stream, including video, all audio, subs, and packet overhead.

If your using 224Kbit/s audio ~2376 is the maxium bitrate for video you can achieve, if your not using subs.

With 2520 for video, you audio is limited to 80 Kbit/s.

Those are the maxium values Philips SCVD authoring toolkit accepts, and is also discussed in the manual.

I-Author follows the same specs, except allows 224Kbit/s audio with 2400 video.

bbMpeg's default mux and encode values are 2376 for video, and 224 for audio, or 2600 combined.

[Heavensent]

the basic thing is to not go OVER 2520
you can play around with it if you want it to be under that bitrate.

thats why we can make a vbr svcd.
with vcd its a different story, it has a fixed bitrate that cannot be
played with (if you want it to be compatible)

so just stick with UPTO 2520 and you are ok.

if you intend to use an authoring program that limits you to a certin
bitrate, you will have to encode the file as demanded by the authoring program.

my advice - just burn with nero, dont add a menu because
you will transfer it to dvd sometime it the futre, so why waste the time?

[cosmin]

Thanks, guys, for the answers.

Unfortunately, I am still confused. SatStorm says that Claim #1 is true, whereas Disturbed1 says that Claim #2 is true (that 2600 is maximum of video *and* audio, and 2778 is actually a maximum of the total stream, including all other possible audio streams and subs).

Can anyone point me to some official (or at least semi-official but more complete) specs? The https://www.videohelp.com/svcd section about SVCD doesn't give me any guarantee of completeness or accuracy - for example, it doesn't mention too much of what Disturbed1 said here.

I don't think I agree with Heavensent:
- If Claim #1 is true, then 2520 is a maximum only if audio has 256kbps (because 2522+256=2778). But if audio has a lower bit rate, say 224kbps, then video can be 2554kbps (because 2554+224=2778).
- If Claim #2 is true, then 2520 is too high. Assuming I am using 224kbps for audio, video cannot be bigger than 2600-224=2376 - which implies that the TMPGEnc setting of 2520 (for video) and 224 (for audio) is wrong!

[adam]

We had a copy of the SVCD specs where I used to work, you can purchase them for about $50.

2600kbits is the maximum bitrate for the video stream only.
2778kbits is the total max bitrate of audio + video + any additional overhead ie: subs.

TMPGenc's default settings are about right. with 2520 vid bitrate and 224 audio you get a total of 2744, but this does't include the additional overhead that will be added during multiplexing.

[cosmin]

Thanks, Adam, for clarification.
Now I wonder why Premiere / MainConcept / bbMPEG are limiting the video stream to 2376kbps. Could it be because ... they misinterpreted the specs?!

[adam]

Well, I can speak for BBmpeg, but it probably applies for the others as well. SVCD scan offsets are required for the disk to comply with the SVCD standards, and these can add quite a bit of overhead to your mpg. By default, BBmpeg adds scan offsets and that would explain why its max bitrate is lower. As for the suggested settings of other programs, they are just that, suggested. Maybe they were misinformed to a certain extent, but they also may just be overcompensating just in case. A couple hundred MBits isn't going to make a huge difference in quality, but it could mean the difference between a disk playing or not.

[cosmin]

As for the suggested settings of other programs, they are just that, suggested.

Hmm... my biggest worry is about TMPGEnc's 2520. People (including myself) take it for granted. Okay, maybe TMPGEnc doesn't add scan offsets that are as big as those of bbMPEG, but even in this case, it may be dangerous to take a TMPGEnc -encoded video stream and mux it with bbMPEG.

Maybe they were misinformed to a certain extent, but they also may just be overcompensating just in case. A couple hundred MBits isn't going to make a huge difference in quality, but it could mean the difference between a disk playing or not.

My point exactly.