MKV Framerate changed

[karussellbremser]

When cutting some seconds from the beginning of an MKV file, the resulting cut file has altered Framerate information: The original was 23.976fps CFR, the cut file is 24.000fps VFR. Shouldn't they be untouched? Using latest Lossless Cut 3.36.0 on Windows 10.

MediaInfo general and video portions (I blanked the some irrelevant values):

Original:
"track": [ { "@type": "General", "UniqueID": ----, "VideoCount": "1", "AudioCount": "1", "MenuCount": "1", "FileExtension": "mkv", "Format": "Matroska", "Format_Version": "4", "FileSize": "14503321545", "Duration": "5960.299", "OverallBitRate_Mode": "VBR", "OverallBitRate": "19466569", "FrameRate": "23.976", "FrameCount": "142904", "StreamSize": "2289020", "IsStreamable": "Yes", "Title": ----, "Movie": ----, "Encoded_Date": ----, "File_Created_Date": ----, "File_Created_Date_Local": ----, "File_Modified_Date": ----, "File_Modified_Date_Local": ----, "Encoded_Application": "mkvmerge v42.0.0 ('Overtime') 64-bit", "Encoded_Library": "libebml v1.3.10 + libmatroska v1.5.2" }, { "@type": "Video", "StreamOrder": "0", "ID": "1", "UniqueID": ----, "Format": "AVC", "Format_Profile": "High", "Format_Level": "4.1", "Format_Settings_CABAC": "Yes", "Format_Settings_RefFrames": "3", "Format_Settings_GOP": "M=3, N=12", "CodecID": "V_MPEG4/ISO/AVC", "Duration": "5960.288000000", "BitRate_Mode": "VBR", "BitRate": "17902528", "BitRate_Maximum": "32294400", "Width": "1920", "Height": "1080", "Stored_Height": "1088", "Sampled_Width": "1920", "Sampled_Height": "1080", "PixelAspectRatio": "1.000", "DisplayAspectRatio": "1.778", "FrameRate_Mode": "CFR", "FrameRate": "23.976", "FrameCount": "142904", "Standard": "NTSC", "ColorSpace": "YUV", "ChromaSubsampling": "4:2:0", "BitDepth": "8", "ScanType": "Progressive", "Delay": "0.000", "StreamSize": "13338028481", "Language": "en", "Default": "Yes", "Forced": "No", "BufferSize": "29999616", "colour_description_present": "Yes", "colour_description_present_Source": "Stream", "colour_range": "Limited", "colour_range_Source": "Stream", "colour_primaries": "BT.709", "colour_primaries_Source": "Stream", "transfer_characteristics": "BT.709", "transfer_characteristics_Source": "Stream", "matrix_coefficients": "BT.709", "matrix_coefficients_Source": "Stream" },

after cutting:
"track": [ { "@type": "General", "UniqueID": ----, "VideoCount": "1", "AudioCount": "1", "MenuCount": "1", "FileExtension": "mkv", "Format": "Matroska", "Format_Version": "4", "FileSize": "14503827608", "Duration": "5949.829", "OverallBitRate_Mode": "VBR", "OverallBitRate": "19501505", "FrameRate": "24.000", "FrameCount": "142904", "StreamSize": "2795083", "IsStreamable": "Yes", "Title": ----, "Movie": ----, "Encoded_Date": ----, "File_Created_Date": ----, "File_Created_Date_Local": ----, "File_Modified_Date": ----, "File_Modified_Date_Local": ----, "Encoded_Application": "Lavf58.45.100", "Encoded_Library": "Lavf58.45.100", "extra": { "ErrorDetectionType": "Per level 1" } }, { "@type": "Video", "StreamOrder": "0", "ID": "1", "UniqueID": ----, "Format": "AVC", "Format_Profile": "High", "Format_Level": "4.1", "Format_Settings_CABAC": "Yes", "Format_Settings_RefFrames": "4", "CodecID": "V_MPEG4/ISO/AVC", "Duration": "5949.819000000", "BitRate_Mode": "VBR", "BitRate": "17902528", "BitRate_Maximum": "37499904", "Width": "1920", "Height": "1080", "Stored_Height": "1088", "Sampled_Width": "1920", "Sampled_Height": "1080", "PixelAspectRatio": "1.000", "DisplayAspectRatio": "1.778", "FrameRate_Mode": "VFR", "FrameRate": "24.000", "FrameRate_Original": "23.976", "FrameCount": "142904", "ColorSpace": "YUV", "ChromaSubsampling": "4:2:0", "BitDepth": "8", "ScanType": "Progressive", "Delay": "0.042", "StreamSize": "13338028481", "Language": "en", "Default": "Yes", "Forced": "No", "BufferSize": "30000000 / 30000000", "colour_description_present": "Yes", "colour_description_present_Source": "Container", "colour_range": "Limited", "colour_range_Source": "Container", "colour_primaries": "BT.709", "colour_primaries_Source": "Container", "transfer_characteristics": "BT.709", "transfer_characteristics_Source": "Container", "matrix_coefficients": "BT.709", "matrix_coefficients_Source": "Container" },

[karussellbremser]

After some investigating, I believe this issue partly to be the result of issue 756: The original amount of frames (as this value is not altered) is divided by the correctly shortened runtime, which results in a higher calculated framerate. (This doesn't explain though why the framerate is changed from CFR (constant framerate) to VFR (variable framerate).)

[mifi]

LosslessCut doesn't really do anything with this metadata, so this is all in ffmpeg's hands.

[mifi]

You could try to reproduce the issue by running the ffmpeg commands from the command line (Help -> bottom -> last ffmpeg commands) and then selectively remove options and see if it changes anything.

[mifi]

See also #1027

[mifi]

I did some testing in #1096 (comment) and it seems like it's happening even with the simplest ffmpeg command ffmpeg -i in.mkv -t x -c copy out.mkv - did you ever find any workaround for it?

[karussellbremser]

My workaround is using TMPGEnc MPEG Smart Renderer 6, sorry.

[mifi]

closing in favor of #1096