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Old 3rd December 2004, 18:48   #31  |  Link
Sir Didymus
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Join Date: Mar 2004
Location: Italy
Posts: 953
Quote:
Originally posted by dragongodz
obviously but if you want more reliable results you do need to do larger/longer encodes(maybe not a whole movie but a reasonbably large section) and to do multiple varied sources. that would show clearer under what conditions OPV may give better results and where it wouldnt. yes a huge task that would take a very long time.
Totally agreed, and happy to see you underline this aspect: never forget the scientific approach. A single cell of a single movie is not sufficient for taking general conclusions.

For the moment let me just complete the first test (now that the whole thread has been "edited" I am a little bit more confident this is feasible). By the way, taking the opportunity to say where this work is assumed to go, and what conclusions are expected from my point of view:

1. The whole test is based on the usage of the SSIM tool. This is a limitation.

2. The test is based on a single cell (6795 frames) of a single movie. This is a big limitation

3. First step (completed) was to generate some tables with encodings produced "starting from" an eclcce file generated by DVD-RB. For the five bitrates of 4250, 3750, 3250, 2750, 2250 Kbit/s it has been executed 9 VBR encodings (from 1+1 to 1+9 passes) and two OPV encodings, finding empirically the Q values better matching the targer bitrates. THIS STEP HAS BEEN COMPLETED USING THE DEFAULT STANDARD QUANTI MAT.

4. Step 3 has been repeated for the bitrates of 3750, 3250, 2750, 2250, 1750, using the Very Low Bitrate Quanti Mat of CCE. (encodings completed, still pending the data analysis.

5. The same, for bitrates of 3250, 2750, 2250, 1750, 1250 should be carried out using both the Ultra Low Bitrate Quanti Mat of CCE and the Notch Matrix (here again just completed the encodings for the CCE Matrix, nothing done with the Notch). Here just want to point out that I think I will use the Notch Matrix with DC precision set to 10 bits, while the recommended is 8 bit, for making omogeneous comparisons with all other encodings performed with DC precision set to 10 bit. I hope this makes the test with Notch still useful. If someone is frequently using the Notch matrix (me not...), please give me some advice...

6. At the end, when all encoding and data analysis will be done based on SSIM, I am very interested in making the same comparisons based on PSTN, as suggestd by Boulder; it shouldn't take too much more time...


EXPECTED CONCLUSIONS (Sorry most are obvious...).

1. Change your feelings and your way of encoding only if you are very confident on what you do; and especially follow what your eyes are telling: if you actually are capable of seeing differences between encodings performed using OPV and 1+3 passes, or 1+9 passes follow what is better for yourself.

2. I think that the discriminatory power of SSIM regarding the bitrate can be accepted as a fact: the different classes of encodings at different bitrates produce different SSIM values.

3. The SSIM tool is actually not discriminating between VBR encodings: for a given bitrate it actually seems all VBR encodings produce similar results.

4. Further conclusions will follow as soon steps 4. 5. and 6. above will conclude...

SD
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