matroska | Matroska format support | Video Utils library

I'll answer my own question, as I've been able to solve the issue with the help of kesh in the comments.

There are basically two things:

• vsync passthrough is required for the input video, to keep the number of frames
• another external tool (MKVToolNix) has to be used twice to extract timestamps from the initial video and apply them to the output

Below is the relevant code to perform the whole operation using python and subprocess. You can use the following line on both input and output video to check that the timestamps are indeed the same for each frame: ffprobe -show_entries packet=pts_time,duration_time,stream_index video.mkv

What you were doing in the just deleted question was correct,

There is not really a need for a subroutine. Delayed variable expansion is needed finally, but it is possible to first assign the fully qualified file name to an environment variable like FileName to avoid troubles with file names containing an exclamation mark.

The rewritten code according to the code posted in the question with some comments:

Your input video stream uses AV1 codec, and as the log says,

MDN Says:

For example, for any MIME type whose main type is text, you can add the optional charset parameter to specify the character set used for the characters in the data. If no charset is specified, the default is ASCII (US-ASCII) unless overridden by the user agent's settings. To specify a UTF-8 text file, the MIME type text/plain;charset=UTF-8 is used.

So, for anything based on text/... you can optionally add the charset.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types#structure_of_a_mime_type

The following update to contentType() function demonstrates one solution.

A for /F command with a set to process the output of a command line results in starting in background one more Windows command processor with %SystemRoot%\System32\cmd.exe /c and the command line appended as additional arguments. Therefore delayed variable expansion is not enabled for this command process running in background as it would be necessary for echo !mkvmergeinfo!. It would be necessary to run the background cmd.exe with option /V:ON left to option /c and the command line to execute. But that is not possible, except running two additional cmd.exe, the first one with /c and a command line which starts with %ComSpec% /D /V:ON /C ... a second cmd.exe as suggested by aschipfl in his comment above.

I suggest to run mkvmerge.exe -i once for each *.mkv file and process the output using just internal commands of cmd.exe like FOR and IF without using find.exe and findstr.exe at all.

Example:

So the secret lied in reading stdout as you dumped the bytes into stdin, since writing to the pipe blocks. Thanks @JimB for helping me figure this out.

You just have to read as you write:

I moved the creation of the MediaRecorder instance to the recurrent function and now it is working properly:

I'm not sure what you mean by "Therefore, it prevents me from passing to a data." but I would use s.split("end") to separate and make othe string operations from there because you would have everything to "end" separated in each index of the array. Maybe using splitlines after for an array of the lines of each block of "start/end".