[FFmpeg-user] MXF XAVC UHD video stream modified while using the -copy option

[Ronan Ricou]

Hello,

I'm trying to remux a MXF XAVC file with the exact same video but only 2 out of the 4 audio tracks.
For that I use this command:
ffmpeg -i INPUT_FILE -c copy -map 0:v -map 0:a:0 -map 0:a:1 OUTPUT_FILE

The thing is, some video data are lost during the remux as my file is smaller than it should be.
If I check with MediaInfo, the video stream bit rate, bits/(pixel*frame) value and stream size are smaller.

Here is the output of the original file:
Video
ID                                       : 2
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High 4:2:2 Intra at L5.1<mailto:Intra at L5.1>
Format settings, CABAC                   : No
Format settings, GOP                     : N=1
Format settings, wrapping mode           : Frame
Codec ID                                 : 0D01030102106001-0401020201323001
Duration                                 : 4 min 30 s
Bit rate                                 : 506 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 50.000 FPS
Standard                                 : Component
Color space                              : YUV
Chroma subsampling                       : 4:2:2
Bit depth                                : 10 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 1.219
Stream size                              : 15.9 GiB (99%)
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                 : HLG
Matrix coefficients                      : BT.2020 non-constant

And of the remuxed file:
Video
ID                                       : 2
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High 4:2:2 Intra at L5.1<mailto:Intra at L5.1>
Format settings, CABAC                   : No
Format settings, GOP                     : N=1
Format settings, wrapping mode           : Frame
Codec ID                                 : 0D01030102106001-0401020201323001
Duration                                 : 4 min 30 s
Bit rate                                 : 500 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 50.000 FPS
Standard                                 : Component
Color space                              : YUV
Chroma subsampling                       : 4:2:2
Bit depth                                : 10 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 1.207
Stream size                              : 15.7 GiB (100%)
Color range                              : Limited
Color primaries                          : BT.2020
Transfer characteristics                 : HLG
Matrix coefficients                      : BT.2020 non-constant

Using current release 3.4.1 and latest nightly (N-89956-gcaa4bd7a9f) does the exact same thing.

Any idea what's happening and how I can prevent this loss?

Many thanks in advance for your help,


Ronan