MP4Box & splitting -- won't do as told

[Virnec]

Greetings.

Not sure if this is the right place for this, but couldn't find an official forum etc. for gpac (which MP4Box is part of).


When splitting mp4-files, mp4box will in most cases not sync at the specified interval.
Quote from gpac's docs:

-splitx StartTime:EndTime : extracts a subfile from the input file. StartTime and EndTime are specified in seconds. Depending on random access distribution in the file (sync samples), the startTime will be adjusted to the previous random access time in the file.

When extracting several chunks sequentially from the same file, each chunk (except the one starting at zero) will begin 1.33 seconds earlier than specified. This will effectively make each new chunk start with the last 1.33 seconds of the previous one.
Now, if you concatenate those files back.... The concatenation will produce a file with 'hiccups' at the joints -- which is not very useful.

I've looked for ways to disable the use of 'sync samples' but failed.
Does anyone know how?


Thanks.

[scarymyth]

I can't help you with sync samples but one thing I do know is that demuxing your file then remuxing again before trying any other processes takes care of a lot of irregularities when trying to use mpbox commands.

When I was having challenges with some basic mp4box processes I reasoned that if mpbox wrote the file then it must conform to what it wants to see in an input file. So before setting any other tasks I demux mp4 file into a filename.h264 and a filename.aac using filename.mp4 -raw. I then remux them back into an ISO compliant mp4 with the -add function in mp4. After doing that I go ahead and run other commands and this cleans up many issues around conformity.

I can post batch file examples should you wish to experiment with this idea.

All the best

Scary

[Virnec]

Old Thread Alert!


Almost two years since I posted this, eh. Time flies


This was one of my wacky experiments..
Basically, the idea was to make a system which could split split a video back to its basic components (don`t ask, I`m just slightly mad x) ).

Later though, I understood that the best practice would be to merge/split the streams outside the container, by just concatenating them. Splitting would be done by using a simple auto-generated textfile, with a single array containing data on the names and sizes of the original files. A program would be fed this list, and cut out the original streams. A simple par2-archive, with just a few blocks of parity, would be supplied to repair any imperfections on each end of the stream.

Cool eh?
Haven`t really taken this any further, but shuldn`t be hard to cook this up with some Python.
Thanks for replying tho!