[FFmpeg-user] why ffplay cannot decode a sequence that can be decoded by ffmpeg

[Zak]

On 2018-06-11 at 5:32 PM EDT, Carl Eugen Hoyos wrote:
> 2018-06-07 23:40 GMT+02:00, mohammed bey ahmed khernache <mohbeyinfo at gmail.com>:
> 
>> My purpose is to calculate some metrics such as: fps, miss rate, etc, of
>> video decoding. So I need only to decode a video without displaying it.
> 
> Sorry for missing this:
> In this case, ffplay is the wrong tool for you, ffmpeg -i input -an -f null -
> may be a better idea.
> 

Okay, I am going to ask the questions that have been on my mind for this 
entire thread:

1. What is the goal of the original email? Frames per second is 
available from ffprobe, right? Does "miss rate" refer to cache misses 
while operating on the compressed video data? Won't the number of cache 
misses depend on many factors, possibly including whether the computer 
hardware is also busy rendering and displaying a video on the screen, 
such that disabling all video display actually will change the "miss 
rate"? This does not seem like a characteristic of the video file 
itself, it seems like a statistic that is only available during a 
specific instance of playing the video with specific software and 
hardware. Or maybe I am misunderstanding. The number of cache misses may 
in practice be exactly the same every time you play a given video on 
certain hardware, but the original email says the test is being run 
remotely on a computer that cannot display video, so any actual playback 
will occur on a different computer that will have different performance, 
unless I am misunderstanding.

2. What does ffmpeg with -f null really do, and how is it different than 
ffprobe?

Thank you,

Zak