Shotcut repeating frames after export

So. I took several mp4 clips, edited them… Everthing looks alright… Until I export my video.

The problem is that after some cuts individual frames appear for 1-3 miliseconds which do not really belong there. I noticed that these frames belong to the corresponding original videos and they were at the site before the cut video. I have however perfectly cut and in the preview in Shotcut also shows no problem with it and the frames do not appear. Only after the export these individual frames appear.

I hope my english wasnt too bad. Any way to fix it? Sure I could simply cut the exported video again, but the problem is that the synch with the music wouldnt fit anymore.

I export in default options and the clips I use have different FPS.

Some information:

ffprobe output

[streams.stream.0]

index=0

codec_name=h264

codec_long_name=H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10

profile=High

codec_type=video

codec_time_base=1001/60000

codec_tag_string=avc1

codec_tag=0x31637661

width=1280

height=720

coded_width=1280

coded_height=720

has_b_frames=2

sample_aspect_ratio=1:1

display_aspect_ratio=16:9

pix_fmt=yuv420p

level=31

color_range=tv

color_space=bt709

color_transfer=bt709

color_primaries=unknown

chroma_location=left

timecode=N/A

refs=4

is_avc=true

nal_length_size=4

id=N/A

r_frame_rate=30000/1001

avg_frame_rate=30000/1001

time_base=1/30000

start_pts=0

start_time=0:00:00.000000

duration_ts=2576574

duration=0:01:25.885800

bit_rate=26.416915 Mbit/s

max_bit_rate=N/A

bits_per_raw_sample=8

nb_frames=2574

nb_read_frames=N/A

nb_read_packets=N/A

[streams.stream.0.disposition]

default=1

dub=0

original=0

comment=0

lyrics=0

karaoke=0

forced=0

hearing_impaired=0

visual_impaired=0

clean_effects=0

attached_pic=0

[streams.stream.0.tags]

language=und

handler_name=VideoHandler

[streams.stream.1]

index=1

codec_name=aac

codec_long_name=AAC (Advanced Audio Coding)

profile=LC

codec_type=audio

codec_time_base=1/48000

codec_tag_string=mp4a

codec_tag=0x6134706d

sample_fmt=fltp

sample_rate=48 KHz

channels=2

channel_layout=stereo

bits_per_sample=0

id=N/A

r_frame_rate=0/0

avg_frame_rate=0/0

time_base=1/48000

start_pts=-1024

start_time=0:00:-0.021333

duration_ts=4123648

duration=0:01:25.909333

bit_rate=2.275000 Kbit/s

max_bit_rate=384 Kbit/s

bits_per_raw_sample=N/A

nb_frames=4027

nb_read_frames=N/A

nb_read_packets=N/A

[streams.stream.1.disposition]

default=1

dub=0

original=0

comment=0

lyrics=0

karaoke=0

forced=0

hearing_impaired=0

visual_impaired=0

clean_effects=0

attached_pic=0

[streams.stream.1.tags]

language=und

handler_name=SoundHandler

[format]

filename=C:\Users\Alex\Desktop\Projects\Projekte am laufen/3HD.mp4

nb_streams=2

nb_programs=0

format_name=mov,mp4,m4a,3gp,3g2,mj2

format_long_name=QuickTime / MOV

start_time=0:00:-0.021333

duration=0:01:25.910000

size=270.575062 Mibyte

bit_rate=26.420069 Mbit/s

probe_score=100

[format.tags]

major_brand=isom

minor_version=512

compatible_brands=isomiso2avc1mp41

encoder=Lavf57.25.100

If you turn off “Parallel processing” in the Export panel, does it help? (You need to re-export in case it is not obvious.)

Doest help. I researched a bit and could it be possible that the bug happens because the clips have different framerates?
I use clips with framerates “25”, “29,97” and “24,875”.

Yes, it might be a problem with mixing framerates, or it might be a problem with the ability to accurately seek on the particular input files exhibiting the problem. Hard to say. Sometimes, H.264 with B-frames are problematic like this.