Beesweet vorbis bitrate or gspot/media info vorbis bitrate?

[jkwarras]

Hi,

I'm a little confused about what is the real bitrate of a vorbis ogg file. Let me explain, if i encode a ac3 movie sound with beesweet, at q0.200, the log file tell me at the end it has encode the file at an 75 kbps average bitrate. At this quality vbr setting it shoul dend up with an average bitrate of 96 kbps, but i supposed that the file didn't need more bitrate;

But when i open the same ogg file in another tool (media info, gspot) it tell me it's a 96 kbps average bitrate. It happens if the sound is mux with the movie or without. So, what is the real bitrate, the one that beesweeet tell me, or the one that tools like gspot or media info tell me?

[TelemachusMH]

If you use the quality compression of Vorbis (which is recommended). It is not compressed with a bitrate in mind. The value you give it is a compression value. It will take the input and compress it X amount. So, the output bitrate it dependent on how compressable the audio is.
In your case, the audio is quite compressable. So, instead of being an 'average' bitrate amount (Your predicted 96bkps) it was more compressable then most audio tracks, and only used the 75kbps.
This doesn't mean that the audio has been saturated though, if you do give it a higher q value it will use more space.
Also, I would guess that GSpot found the q value you used, and it used the same prediction values that besweet did.

TelemachusMH

[jkwarras]

Originally posted by TelemachusMH
If you use the quality compression of Vorbis (which is recommended).

Yes i do.

In your case, the audio is quite compressable. So, instead of being an 'average' bitrate amount (Your predicted 96bkps) it was more compressable then most audio tracks, and only used the 75kbps.

I know, as it quality based, the average bitrate is just an indication, but i was confused about the difference beetween gspot and beesweet information.

Also, I would guess that GSpot found the q value you used, and it used the same prediction values that besweet did.

That's what i would also guess, that in some manner gspot nd other tolls like hat checks what q setting has been used to encode the file instead of analyse the file and show the real average bitrate.

Another thign i'm experimenting is when using q vorbis enconding, i always (and i mean it) end with an average encoded around 10kbps less than the predicted one; i.e if i use 64kbps (q.001) i end up with +-55 kbps. It's this something usual?

Regards

[TelemachusMH]

It happens to me all the time. It just depends on how compressable it is. I have also had a few tracks come out higher too. It just varies.

TelemachusMH

[ChristianHJW]

GSpot would have to scan the complete file to know the bitrate exactly, so it only uses the q value to give you an idea .... trust BeSweet in this respect, it knows the actual file size of the audio stream and the length, and such the real bitrate ;) ....

[dTb]

Through the ogg webpage I downloaded something called VorbisExt, it gives you an extra two tabs when right clicking on an ogg file and selecting properties. These extra tabs give you a lot of info on the file. May be worth you checking out.
It's normal for movie audio tracks encoded to ogg to have lower average bitrates, I think it's due to there often being a lot of silence in the average movie soundtrack.