On Sat, Sep 20, 2003 at 10:05:35AM -0700, Steven M. Schultz wrote: > > On Sat, 20 Sep 2003, Bernhard Praschinger wrote: > > > Audio: ( Samplerate * Channels * Bitsize ) / (8 * 1024) > > Video: (width * height * framerate * quality ) / (200 * 1024) > > > > You have to add both values together. To get the datarate in kb/sec. > > The Video formula is not giving me answers that look right. > > For 640x480 and 29.97 frames/sec I get: > > (640 * 480 * 29.97 * 1.0 ) / (200 * 1024) = 50.57 > > 50 kb/sec? Wow -that's amazing compression ;)
This formula would work for raw (uncompressed) compression. But for compression, it does not properly compensate for the amount that the compression codec can squeeze out of the video. In fact, it will produce differing values for exactly the same quality depending on which DC10+ driver (0.8 or 0.9) is being used to capture. This is because the definition of the driver quality setting changed between 0.8 and 0.9, and the old (0.8) driver's quality setting of 100 is equal in quality to the new driver's quality setting of 50. But plugging 50 vs. 100 into the formula for "quality" will give different numbers. > For audio it works out better. The DC10 produces PCM audio? Is it > at 44100 or 48000 for the sample rate? Or is it selectable? Actually, the DC10+ card itself contains no audio input/output circuitry at all. A separate sound card is needed for audio capture. > 48000 * 2 * 2 / (8*1024) = 187.50 (~1536000 bits/sec) which > is the correct number. This is because PCM audio is uncompressed, so the data rate is exactly the sample rate times the resolution times the channels. > If the video formula is from the howto section then there's a > typo or something that is producing very low numbers. It's not a typo, except I'm not sure why the 200 is multiplied by 1024 in the divisor. It just does not properly account for compression differences. ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ Mjpeg-users mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/mjpeg-users
