How can I make ffmpeg be quieter/less verbose?

I haven't tested it out, but I see an option in the man page to do:

ffmpeg -loglevel panic [rest of your ffmpeg stuff]

Should make it so only serious errors are logged, in theory

Here you have loglevels from the source code (FFmpeg version 0.10.2.git)

const struct { const char *name; int level; } log_levels[] = {
        { "quiet"  , AV_LOG_QUIET   },
        { "panic"  , AV_LOG_PANIC   },
        { "fatal"  , AV_LOG_FATAL   },
        { "error"  , AV_LOG_ERROR   },
        { "warning", AV_LOG_WARNING },
        { "info"   , AV_LOG_INFO    },
        { "verbose", AV_LOG_VERBOSE },
        { "debug"  , AV_LOG_DEBUG   },
    };

I have used with success the following (newest FFMPEG Version at time of writing):

-nostats -loglevel 0

Then it is absolutely quiet in my usage scenario.

ffmpeg -loglevel error [other commands]

This hides the banner and only displays errors. Use -loglevel warning if you would like to see warnings.

Tested in Ffmpeg 3.0.2.

From the documentation:

-loglevel [repeat+]loglevel | -v [repeat+]loglevel

Set the logging level used by the library. Adding "repeat+" indicates that repeated log output should not be compressed to the first line and the "Last message repeated n times" line will be omitted. "repeat" can also be used alone. If "repeat" is used alone, and with no prior loglevel set, the default loglevel will be used. If multiple loglevel parameters are given, using ’repeat’ will not change the loglevel. loglevel is a string or a number containing one of the following values:

‘quiet, -8’

Show nothing at all; be silent.

‘panic, 0’

Only show fatal errors which could lead the process to crash, such as and assert failure. This is not currently used for anything.

‘fatal, 8’

Only show fatal errors. These are errors after which the process absolutely cannot continue after.

‘error, 16’

Show all errors, including ones which can be recovered from.

‘warning, 24’

Show all warnings and errors. Any message related to possibly incorrect or unexpected events will be shown.

‘info, 32’

Show informative messages during processing. This is in addition to warnings and errors. This is the default value.

‘verbose, 40’

Same as info, except more verbose.

‘debug, 48’

Show everything, including debugging information.

‘trace, 56’

By default the program logs to stderr, if coloring is supported by the terminal, colors are used to mark errors and warnings. Log coloring can be disabled setting the environment variable AV_LOG_FORCE_NOCOLOR or NO_COLOR, or can be forced setting the environment variable AV_LOG_FORCE_COLOR. The use of the environment variable NO_COLOR is deprecated and will be dropped in a following FFmpeg version.

The following worked for me on macOS:

ffmpeg -v quiet

or to only see the progress:

ffmpeg -v quiet -stats

ffmpeg -loglevel error -hide_banner -nostats

Just the errors, nothing else.

I personally like this best;

ffmpeg -loglevel warning -hide_banner -stats

It gives only warnings and errors, but also shows the progress of work.

You can pipe stderr through grep. For example, if you wanted to remove the configuration info, you could do it like this:

% ffmpeg -i infile.avi -s 640x480 outfile.avi >/dev/null 2>&1 | grep -v configuration:

This is a little cheap to go about it, but appending >/dev/null 2>&1 is a sure way to keep ffmpeg silent in the shell.

Example

ffmpeg -f x11grab -y -r 24 -s 800x600 -i :0.0+1366,100 -f oss -i /dev/dsp3 -sameq ./out.avi >/dev/null 2>&1

More info about bash output

These measures don't hide the Codec banner (even with "-loglevel 0"). For hiding the H.265-banner it would look like this:

-vcodec libx265 -x265-params log-level=error

All the answers are a bit old at my time of writing, so for new version in 2021, -loglevel warning dumps a lot of hex codes, and you cannot see the warnings. -loglevel error also dumps lots of hex, you cannot see the 'errors'. -loglevel fatal runs fine but slowly. Perhaps it expects some output. -loglevel panic runs fast, but you miss out on fatal errors. The best you could use, is:
Windows (cmd/dos) & Python3:

from os import system
for file in list:
    system('ffmpeg -hide_banner -loglevel fatal -nostats (your options)>file.txt')

Unix & Python3:

from os import system
for file in list:
    system('ffmpeg -hide_banner -loglevel fatal -nostats (your options)&>file.txt')

Now, search which files are not blank.

from os import stat
for file in list:
    if stat('file').st_size == 0:
        continue
    else:
        print(file)

Check those files which have some output.