z mych skusenosti ma bezstratove video cca 2gb/min zalezi na rozliseni a frameratu. v dobe kdy jsem mel jeste upc a linku z malym uploadem jsem dycky videa pred nahranim na utube prekonvertoval, pouzil jsem treba tenhle prikaz:
ffmpeg -r 20 -i dwarf00%4d.png -i ../dwarf.mp3 -c:v libx264 -preset slow -crf 5 ../dwarf2.mkv
vysledny sopubor mel asi 12 mb a po te co jej utube znovu prekonvertoval tak to porad vypada slibne viz:
http://www.youtube.com/watch?v=3lBQoe1hihczajimavy je parametr crf:
Constant Rate Factor (CRF)
This method allows the encoder to attempt to achieve a certain output quality for the whole file when output file size is of less importance. This provides maximum compression efficiency with a single pass. Each frame gets the bitrate it needs to keep the requested quality level. The downside is that you can't tell it to get a specific filesize or not go over a specific size or bitrate.
1. Choose a CRF value
The range of the quantizer scale is 0-51: where 0 is lossless, 23 is default, and 51 is worst possible. A lower value is a higher quality and a subjectively sane range is 18-28. Consider 18 to be visually lossless or nearly so: it should look the same or nearly the same as the input but it isn't technically lossless.
The range is exponential, so increasing the CRF value +6 is roughly half the bitrate while -6 is roughly twice the bitrate. General usage is to choose the highest CRF value that still provides an acceptable quality. If the output looks good, then try a higher value and if it looks bad then choose a lower value.
Note: The CRF quantizer scale mentioned on this page only applies to 8-bit x264 (10-bit x264 quantizer scale is 0-63). You can see what you are using with x264 --help listed under Output bit depth. 8-bit is more common among distributors.
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