[FFmpeg-devel] [PATCH] Fix loss of precision for silencedetect on large files

[Allan Cady]

Trying a desktop mail client instead of webmail.

On 3/27/2019 11:19 AM, Michael Niedermayer wrote:
>
> this breaks make fate
>
> also if fate is updated it should be ensured it still checks enough precission
> and that it does produce the same results (fate passes) on all relevant
> platforms. This change may bring non significant differences into significance
>
> thanks
>
> [...]


OK so I spent some more time familiarizing myself with the code and 
tests, and it's clear that making the change the way I did would 
probably break dozens of tests, because the function I changed, 
av_ts_make_time_string, is referenced (by its convenience macro 
av_ts2timestr) in many files (I count 21) and dozens of lines of code, 
in libavfilter, fftools, and libavformat.

As an alternative, I tried making a modified & renamed copy of 
av_ts_make_time_string/av_ts2timestr, and referencing that copy in 
af_silencedetect.c, leaving other references to the original function 
unchanged. In this case, FATE fails just a single test, 
filter-metadata-silencedetect. I then modified the reference output file 
(tests/ref/fate/filter-metadata-silencedetect) to match the changed 
output, and all tests then pass.

In looking at other uses of av_ts2timestr, it's clear av_ts2timestr was 
intended for general purpose use.

So at this point I could use some guidance from the wizards as to the 
best way to proceed. Not knowing any of the history or thinking that 
went into the design, I don't know if it makes the best sense to use the 
"%.6g" format for all those other timestamps, but I feel strongly that 
it's a poor choice for silencedetect (and probably other *detect 
filters), for the reason I explained originally. Is there possibly 
another way to get the result I want without modifying the code? I can 
imagine maybe a format specifier as a filter parameter -- is there any 
precedent for this?

Open to suggestions. Thanks all.

Allan