Avidemux video cutting bug

[nanolab]

I'm trying to cut .MTS video from Panasonic LX7 without reencoding.
I use I-frames as A and B to trim, but in result video there is something wrong at the beginning.
Then (after few frames) the video becomes good.





Media Info:

General
ID                             : 0 (0x0)
Format                         : BDAV
Format/Info                    : Blu-ray Video
File size                      : 1 008 MiB
Duration                       : 5mn 2s
Overall bit rate mode          : Variable
Overall bit rate               : 28.0 Mbps
Maximum Overall bit rate       : 28.0 Mbps

Video
ID                             : 4113 (0x1011)
Menu ID                        : 1 (0x1)
Format                         : AVC
Format/Info                    : Advanced Video Codec
Format profile                 : High@L4.2
Format settings, CABAC         : Yes
Format settings, ReFrames      : 2 frames
Codec ID                       : 27
Duration                       : 5mn 2s
Bit rate mode                  : Variable
Bit rate                       : 26.5 Mbps
Width                          : 1 920 pixels
Height                         : 1 080 pixels
Display aspect ratio           : 16:9
Frame rate                     : 50.000 fps
Color space                    : YUV
Chroma subsampling             : 4:2:0
Bit depth                      : 8 bits
Scan type                      : Progressive
Bits/(Pixel*Frame)             : 0.256
Stream size                    : 961 MiB (95%)

Audio
ID                             : 4352 (0x1100)
Menu ID                        : 1 (0x1)
Format                         : AC-3
Format/Info                    : Audio Coding 3
Mode extension                 : CM (complete main)
Format settings, Endianness    : Big
Codec ID                       : 129
Duration                       : 5mn 2s
Bit rate mode                  : Constant
Bit rate                       : 192 Kbps
Channel(s)                     : 2 channels
Channel positions              : Front: L R
Sampling rate                  : 48.0 KHz
Bit depth                      : 16 bits
Compression mode               : Lossy
Stream size                    : 6.92 MiB (1%)

Text
ID                             : 4608 (0x1200)
Menu ID                        : 1 (0x1)
Format                         : PGS
Codec ID                       : 144
Duration                       : 5mn 1s

[theewizard]

IDK
i use Video Redo for mts files from my PVR
i use avidemux for other file types
maybe make your cut a little bit earlier
then TRIM with avisynth , IF you making DVDs using av2dvd

i just tried to edit/cut 4:44 seconds of a 60min HDTV recording with avidemux
it gave an error of encoder not responding
and i was doing a straight video copy
i did not pick I frames for the cut points, and it would not edit at all

IMO change tools

[nanolab]

IDK
i use Video Redo for mts files from my PVR

Thanks.
Just tried it, but it produces exactly the same damaged video at the beginning frames.

[jagabo]

Probably open GOPs. With open GOPs the last B frames of the GOP can reference the I frame of the next GOP. That I frame has to be decoded before those B frames are decoded. So the B frames are stored AFTER the I frame within the file:

presentation order: ...PBBI...
stored order: ...PIBB...
after cutting: ...IBB...

Without the preceding P frame those B frames can no longer be decoded properly. And since they are displayed before the I frame you get junk in the first few frames.

[nanolab]

after cutting: ...IBB...

Without the preceding P frame those B frames can no longer be decoded properly. And since they are displayed before the I frame you get junk in the first few frames.

Thank you very much!
You are right, this is exactly what I have.

But how can I fix that?

[jagabo]

You have to reencode the cut GOPs. You could use an editor that reencodes the entire video but that will be time consuming and decrease quality of the entire video. Or you can use a smart editor like VideoRedo that only reencodes the cut GOPs (the rest of the video is only remuxed).