merge multiple mp4(h264) video the time frame get reduce by 10%

[redsunbird]

Hi all
Pardon for my English language, when I try to merge mp4(h264) video the time frame get reduce by 10% for example. If I have two video of 15 second each. When I combine it has to give me 30 sec. but the final output video length is 27 sec only. But by comparing the original video and merge video both are equal.

While merging the video I got list of error like skipping frame

Pos: 52.4s 1452f (86%) 17.63fps Trem: 0min 39mb A-V:0.084 [5459:3]
Skipping frame!
Pos: 52.7s 1462f (87%) 17.74fps Trem: 0min 39mb A-V:0.084 [5459:3]
Skipping frame!
Pos: 53.1s 1472f (88%) 17.84fps Trem: 0min 39mb A-V:0.084 [5463:3]
Skipping frame!
Pos: 53.4s 1482f (97%) 17.95fps Trem: 0min 35mb A-V:0.084 [5454:3]
Skipping frame!
Pos: 53.8s 1492f (98%) 18.05fps Trem: 0min 35mb A-V:0.084 [5456:3]
Skipping frame!
Pos: 54.2s 1502f (99%) 18.15fps Trem: 0min 35mb A-V:0.084 [5464:3]
.......


I am clipping the video using ffmpg and merging the video using mencoder.

ffmpeg query for clipping the wmv video file and convert it to mp4
================================================== =================

ffmpeg.exe -ss 00:34:2.30 -t 00:00:15.00 -i "F:\GAMES\Sample.wmv" -r 25 -b 3000k -croptop 0 -cropbottom 0 -cropleft 0 -cropright 0 -y "C:\output1.mp4"
ffmpeg.exe -ss 00:54:2.30 -t 00:00:15.00 -i "F:\GAMES\Sample.wmv" -r 25 -b 3000k -croptop 0 -cropbottom 0 -cropleft 0 -cropright 0 -y "C:\output2.mp4"

Merging query in mencoder
======================
mencoder.exe "C:\output1.mp4" "C:\output2.mp4" -o "C:\\combineVideo.mp4" -of lavf -lavfopts format=mp4 -vf harddup -oac copy -ovc lavc -lavcopts acodec=copy:vcodec=mpeg4:vbitrate=8000


any help would be appreciated, thank in advance.

[smrpix]

It appears you have variable frame rate video -- there will be some rounding error converting it to a constant frame rate. Hence, the dropped frames.

[redsunbird]

Hi smrpix,
First of all thank for the reply. I am not much familiar on video processing. i increase the frame rate then i got the error duplicate frame. which i have shown below

Pos: 0.7s 18f ( 0%) 0.00fps Trem: 0min 52mb A-V:0.033 [0:64]
1 duplicate frame(s)!
Pos: 1.6s 44f ( 0%) 0.00fps Trem: 1min 109mb A-V:0.034 [5732:64]
1 duplicate frame(s)!
Pos: 2.5s 69f ( 1%) 0.00fps Trem: 1min 141mb A-V:0.030 [5384:64]
1 duplicate frame(s)!
Pos: 3.4s 94f (17%) 71.48fps Trem: 0min 11mb A-V:0.027 [5018:64]
1 duplicate frame(s)!
Pos: 4.1s 113f (33%) 72.39fps Trem: 0min 7mb A-V:0.034 [4931:64]
1 duplicate frame(s)!
Pos: 5.0s 138f (46%) 74.43fps Trem: 0min 6mb A-V:0.030 [4829:64]
1 duplicate frame(s)!

can u spread some light on this issue

thanks in advance