Hi to all
I need a little help from you, experts :-)
I work with hi-quality screencast captured in my recording studio on WinXP using camorama; the produced screencasts use XVID video codec, the average video bit rate used is about 350 Kb/s,the fps=25,the dimension is 1438x862, audio is wav;
Usually, after i've recorded a screencast, the only thing i do is to use VirtualDub to compress in a lossy format (mp3 320 Kb/s) the audio stream and copy the video stream (so i don't re-encode the video stream).
The video quality of the obtained screencasts is absolutely EXCELLENT (i mean crystal clear)and the weight is really small, about 300 MB for an hour of video;
Unfortunately, sometimes i've the need to put a .png "picture frame" on the screencasts so i've to use kdenlive (at home on Ubuntu) to put it on and so i'm obliged to re-encode the video-stream;
The problem is that i can't get a decent quality without the exported video becoming of huge dimensions, a lot greater than the source file;
To be precise in kdenlive i use libx264 to encode the video stream and the average bit rate i aim to obtain "almost-decent" quality is about 1300Kb/s, so the new file weight becomes about 750 MB for an hour a video!!!
...now i understand that recompress with h264 an already compressed video (XVID is a lossy format i know) worsens the quality a bit but 1300 Kb/s with libx264 to match the quality of the source at 350 Kb/s with XVID isn't a bit too much????
on the other hand if i try to impose a bit rate lower than 1300 Kb/s, for example the same of the source file 350 Kb/s, the quality is absolutely unwatchable...
This happens even if i try to use the libxvid encoder in kdenlive instead that libx264, indeed it's much worst than libx264, in weight and quality...Suggestions?
This is the self-made preset i use in kdenlive to exports my screencasts:
f=avi acodec=libmp3lame ab=320k ar=44100 pix_fmt=yuv420p vcodec=libx264 qcomp=1 qdiff=4 subq=7 qmin=1 qmax=26 s=1438x862
I've extrapolated this working preset after many attempts!!! If you try to remove from this preset the parameters "qcomp=1 qdiff=4 subq=7 qmin=1 qmax=26" and put in place only the parameter b= 1300 Kb the changed preset continuos to operate but produce an avi file without the video stream!!!In ffmpeg instead isn't necessary to declare al that parameters!! Why??? Is this a kdenlive bug??
I use version 0.7.8-2 of kdenlive and version 4:0.6.1-2 of ffmpeg.
Forgive the slowness of the topic, english isn't my native language, i'm italian :-D
Thanks and a virtual beer to those who help me! :-D