FFMPEG why in -vcodec copy I get a progressive speed degradation?

[marcorocchini]

Hi ***

v:\automazioneclip\core\ffmpeg64bit332.exe -y -threads 12 -y -f concat -safe 0 -i concatList.txt -filter_complex "[0:1] [0:2] amerge" -vcodec copy -c:a pcm_s24le -aspect 16:9 concatHD.mov

where concatList.txt is:

file 'V:\recanati\C0003.MXF' 
file 'V:\recanati\C0005.MXF' 
file 'V:\recanati\C0008.MXF' 
file 'V:\recanati\C0010.MXF' 
file 'V:\recanati\C0013.MXF' 
file 'V:\recanati\C0015.MXF' 
file 'V:\recanati\C0016.MXF' 
file 'V:\recanati\C0017.MXF' 
file 'V:\recanati\C0018.MXF' 
file 'V:\recanati\C0019.MXF' 
file 'V:\recanati\C0020.MXF' 
file 'V:\recanati\C0021.MXF' 
file 'V:\recanati\C0022.MXF' 
... ...
file 'V:\recanati\C0116.MXF'

this MXF's are xdcam hd 4:2:2 video files.

At the beginning of encoding speed is good (300 fps, 11x) but after some seconds the speed go down to 95 fps and more down


[Attachment 42383 - Click to enlarge]

Why? thanks

[jagabo]

Probably because your disk cache is full so you're reduced to the actual write speed and seek time of the drive(s).

[pandy]

set destination to different physical drive and compare results - almost sure that jagabo is right.

[marcorocchini]

[Attachment 42387 - Click to enlarge]

I have try on a different disk drive, same falling down but from 16x to --> 9x (instead of 11x-->3x).

Is not costant, but maybe is normal

thanks

[jagabo]

Your video is about 52000 kbps. Mulitply by 9.5x, then divide by 8 to get KB/s and you get about 60000 KB/s, or 60 MB/s. That's typical for continuous writing to a hard drive (depending on the interface, the size of the drive, and what part is being written to).