Recoding HTDV to DVD file sizes?

[thymej]

Can someone explain to me why one re-encoder makes a converted .ts file to .vob half the size when using all the same parameters: bit-rate=9.7M, res=720x480, AR=16:9, Sound=AC3-5.1@48Ksample&384bit-rate?

Using SuperC (GUI for FFMpeg) and setting it to the above parameters, a 45sec .ts test file re-encodes to a VOB size of 18MB.

Using HDTV1DVD (cant set the parameters but they happen to be the same as above except HDTV2DVD makes the bit-rate=7.8M. The same 45sec .ts test file is 40-45MB.

With the same parameters except for the bit-rate, why would a high bit-rate with FFmpeg make a smaller re-encode vob file then the lower bit-rate vob of the HDTV2DVD? I thought bit-rate was like the quality of the video?

What am I missing, am new here to this re-encoding stuff?

ThymeJ

[ChrissyBoy]

There are many parameters to ffmpeg which influence the resultant size.

@ 7800kbs you should be getting:

45 (secs) * 7800/8 KB
Which is ~ 44MB +plus the audio

If super comes in at less than half that – I would say that it is using non ideal parameters to ffmpeg/avcodec

[thymej]

Thx for the responses

I read another post that you said the bit-rate of 7800 was used for compatibility. Does that mean that some dvd players might have a harder time playing back bit-rates that are higher the 7800?

What is a good program to show the true bit-rate of a given vob file?
My SuperC 45sec test in VideoRedo ctrl-L info screen says its 9000+ but HDTV2DVD 45sec test file shows as 7800. If files size = bit-rate * 45sec formula above, the HDTV2DVD seams more true to what VideoRedo is telling me.

[ChrissyBoy]

Thx for the responses

I read another post that you said the bit-rate of 7800 was used for compatibility. Does that mean that some dvd players might have a harder time playing back bit-rates that are higher the 7800?

No. ffmpeg can sometimes create bitrate spikes (i.e. bitrate going above the set max). Some players may not like this. Most are oblivious to it. So a cautious setting of 7800 was used to make sure that even these spikes don't go over the DVD max (of ~9800).

What is a good program to show the true bit-rate of a given vob file?
My SuperC 45sec test in VideoRedo ctrl-L info screen says its 9000+ but HDTV2DVD 45sec test file shows as 7800. If files size = bit-rate * 45sec formula above, the HDTV2DVD seams more true to what VideoRedo is telling me.

The nominal bitrate is written in the mpeg headers. This is the max value set in the encoder. It really has no bearing on the true bitrate. (you could tell an encoder to encode some end credits @ 8000kbs. This would be the nominal bitrate and you would see this in VRD etc. But the actual bitrate would be lower (as most of the frames a black))

So you get (from VRD):



but the actual bitrate needs to be deduced by parsing the file, (from gspot):