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Old 31st May 2016, 10:35   #1  |  Link
OvejaNegra
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some general questions about encoding with x264

crf vs 2pass: Lets say i encode a test video using crf 18. The resulting file es 4GB. Now i encode the same material using 2pass and calculating the bitrate to produce a 4GB file. I have now two files of the same size.

1- Which one has better bitrate distribution (of course its a very bad question): which one will have better overall quality?

In theory 2 pass should take bitrate from high motion scenes (higher quantizers) and give it to low/ regular motion scenes (lower quantizers) creating more quality as perceived by the user (since high motion scenes are difficult to watch in detail). on the other side, crf should give more average quantizer distribution, not so good loking slow scenes but better fast motion scenes = stable quality over the video (in a more practical way than using constant quantizer).

BUT im very sure im wrong and crf is better thant using 2 pass, right?

(im talking about quality, dont care about size fitting right now).

2- Is possible to create a file using crf and at the same time comply with level 3.1 (for example) and vbv constraints? Wikipedia specify a max of 17,500 kbits for level 3.1 on high profile. let's say i want to comply with that and some vbv restraints for some device AND use crf at the same time, it's possible?


3- If i want to encode to constant quantizer (for archival purposes) and im happy with ... qp 10. Are there any other settings i need to touch? Should i set pbratio to 1.0, or simply disable bframes?


4- If im encoding a 720p and set the level to 4.1, is that wrong, or i should set the level to 3.1 and vbv-maxrate to 17,500, 000 to be REALLY level compliant? (info from the wiki).

5- Using 2pass encoding, is possible to adjust the bitrate redistribution: Take bitrate from low motion scenes and give it to fast motion scenes?


6- The same for crf: can i control the "quality" distribution?


7- How should compress a video if i want to stream it at 3mb (for example) whit 5 seconds of pre-buffer? (for example, im not using audio, just video). or simply transmit in real time over specific bandwithd limitations


8- I encode anime with the "film" tuning because i like the grain retention, what settings should i "take" from the animation tune without affecting that? bframes and refs? Can anyone provide and example cli?

9- How can i encode at specific bitrate, for example 3mbs BUT without ANY vbr, i dot care if the compression jumps from q10 to q30 from one frame to another as long as it stays at 3mbs ALL THE TIME, constant bitrate, REALLY constant (it will look horrible, i know but i need it to test something)


10- I was reading this: http://www.chaneru.com/Roku/HLS/X264_Settings.htm but is not updated since 2011


thanks for everything, sorry if i mispelled something.
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