Does a files resolution affect conversion speed?

[perdomot]

Wondering if it takes longer to convert an mkv file that has high definition video in it than one that has 480p video. I use avidemux to convert my mkv files for my ipod touch and some take 3-4 minutes while others take 9-10 minutes. Is this possible or do other factors affect speeds? Thanks.

[lordsmurf]

Yes, it does. Compare a 352x480 encode to a 720x480 encode, even if bitrates are the same. It takes longer. Changing resolutions takes even more time.

[jagabo]

Input frames size has a small effect on encoding speed. Output frame size has a large effect. Other factors have an effect too (complexity of video, encoder settings, etc.)

[perdomot]

So going from a 1280 x 720 mkv file to a 480 x 272 mp4 file would take longer than if the mkv was a smaller resolution?

[jagabo]

Yes. First the larger frame takes longer to decompress. Then it must be downsized to the new resolution. Both of those steps take time. Usually not a lot compared to the time it takes to compress the results though.