2014-10-16, 13:00
(2014-10-16, 05:22)menakite Wrote: I'm curious now - based on the name, I'd say that it limits the HDMI clock changes, and I assume that 50 is smaller than the default. Was the default value increased in recent firmwares? Also, why does this only affect a certain frame rate?
Default is 175 (ppm). It has not changed for a long long time.
Framerate is not significant, but how well the video timestamps and audio timestamps match the data is significant.
Run with mmal, sync video to display and set A/V sync to resample and watch the codec info.
The "rr" parameter shows how much audio needs to be resampled to keep the audio and video clocks synced.
While omxplayer uses a different algorithm, it still has to do a similar compensation.
It alllows up to 0.1% adjustment in HDMI pixel clock, but limits each change step to that specified by hdmi_clock_change_limit.
hdmi_clock_change_limit=50 equates to allowing 0.005% hdmi clock adjustment per step.
I suspect that either your 25Hz videos are encoded in such a way that the timestamps require significant adjustment (can be verified with "rr" number varying from 1.00 or oscillating),
or your receiver is more fussy in that mode.
Note: The default settings work fine for 99% of TVs/receivers - there are just some models that are unusually fussy - what receiver are you using?