FFMPEG Splitting MP4 with Same Quality

Question

I have one large MP4 file. I am attempting to split it into smaller files.

ffmpeg -i largefile.mp4 -sameq -ss 00:00:00 -t 00:50:00 smallfile.mp4

I thought using -sameq would keep the same quality settings. However, I must not understand what that does.

I'm looking to keep the same quality (audio/video) and compression with the split files. However, this setting makes the split files much larger.

What flag(s) do I need to set to keep the same quality and attributes in the split files while maintaining the same quality to size ratio?

For instance if my original file is about 12 GB and is 1920x1080 with a bitrate of 10617kbps and a framerate of 23 frames/sec and 6 channel audio with 317kbps, I would like the split files to be the same only a third of this size (if i split it into three pieces).

Answer 1

If you want to just split the video without re-encoding it, use the copy codec for audio and video. Try this:

ffmpeg -ss 00:00:00 -t 00:50:00 -i largefile.mp4 -acodec copy \
-vcodec copy smallfile.mp4

Note that this only creates the first split. The next one can be done with a command starting with ffmpeg -ss 00:50:00.

This can be done with a single command:

ffmpeg -i largefile.mp4 -t 00:50:00 -c copy smallfile1.mp4 \
-ss 00:50:00 -c copy smallfile2.mp4

This will create smallfile1.mp4, ending at 50 minutes into the video of largefile.mp4, and smallfile2.mp4, starting at 50 minutes in and ending at the end of largefile.mp4.

Answer 2

An Alternate way of doing it is:

// create a 2-min clip
ffmpeg -i input.mp4 -ss 00:10:00 -to 00:12:00 -c copy output.mp4

/**
* -i  input file
* -ss start time in seconds or in hh:mm:ss
* -to end time in seconds or in hh:mm:ss
* -c codec to use 
*/

The quality of the file stays the same because we use-c copy to copy the original audio + video streams to the output.

Reference, List of commonly used FFmpeg commands: DigitalFortress