[FFmpeg-user] How can I force a 360kHz time base?

[Mark Filipak (ffmpeg)]

On 2021-02-27 03:29, Carl Eugen Hoyos wrote:
> Am Sa., 27. Feb. 2021 um 06:34 Uhr schrieb Mark Filipak (ffmpeg)
> <markfilipak at bog.us>:
> 
>> Question: Why would testsrc.mpg have been created with non-zero timestamp for frame 0?
> 
> Nothing in the MPEG specification requires the first frame to have
> a timestamp of 0, so whatever the design decision was, it is not
> wrong.

Hi, Carl Eugen, thank you.

I created testsrc.mpg via this script command:
ffmpeg -f lavfi -i testsrc=duration=5:size=1280x720:rate=30000/1001 testsrc.mpg
The 1st PTS is 48003 -- I don't have a tool with which I can confirm this at the bit level, but it's 
what ffprobe reports. Why would ffmpeg do that?

And do you know why this:
ffmpeg -i testsrc.mpg -codec copy testsrc.mkv
fails?