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Datarates, squeeze and wmv encodes….
hi guys – I’ve just been making some WMV9 encodes in Sorenson Squeeze 4.3 on a PC. I’ve been asked to supply a specific datarate of less than 226Kbps. Now if I set up squeeze to have 180Kbps for the video and 48Kbps for audio it will tell me the total will be 226Kbps. Great… for now…
so I do the encode, and the file comes out at 12.6MB – and I test it (on a mac with flip4mac). If I go to the movie properties it says that the datarate is 359Kbps.
So what’s the go? why would they differ so much? any thoughts on this one would be great.
Thanks!
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4 Replies
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You don’t say how long the videos are. Sometimes movie properties calculations are off. The total
size of the video and audio combined might show up a bit higher (for overhead), but not that much. Multiply
the data rate you select by the length of the video in seconds to get a close idea of it’s real data rate.
Ed -
There has been a long standing bug in the F4M components in the way the decoder determines the bit rate of the file. Essentially, you can’t trust what you see in QT’s Info window when using F4M to decode. I believe it has to do with how the F4M decoder reads the bit rate based on what the buffer settings in the encode were; which depending on how full the buffer is when it reads the bit rate, can vary greatly, especially for VBR encodes. And since WMP on the PC doesn’t actually tell you the bit rate of the file, but rather the bit rate as set in the metadata, the only real way to determine actually bit rate for a clip is to use an application like Inlet Semaphore. https://www.inlethd.com/products/semaphore.html
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Won’t ASFView show you average and max bit rates in addition to the bit rate in the metadata? Kinda makes ASFView “weak” if it can’t show you actual bit rate.
Encoders like Episode can show you frame by frame bit rate. Would be nice if such tool existed on the Mac as a stand alone. -
In what I have seen in ASF Viewer in the past is still the same, then no, it doesn’t show you the “actual” bit rate. But maybe I am missing something? ASF Viewer is nice though for some of the stats it reports, and while we’re on that line, then I could suggest using a free binary viewer for those who are budget concious. With a binary viewer, you can go frame by frame on what each frame bit rate and size is. This is where Semaphore makes nice, as it can do all of this visually and efficiently with the use alerts and batch reporting.
And you are right about Episode being able to show you the rates after an encode was completed with the app. That is a very nice feature! But it would still be hard to correctly calculate the average bit rate of the entire clip.
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