Você pode usar a opção -report . De a documentação :
‘-report’
Dump full command line and console output to a file named program-YYYYMMDD-HHMMSS.log in the current directory. This file can be useful for bug reports. It also implies -loglevel verbose.
Setting the environment variable FFREPORT to any value has the same effect. If the value is a ’:’-separated key=value sequence, these options will affect the report; options values must be escaped if they contain special characters or the options delimiter ’:’ (see the “Quoting and escaping” section in the ffmpeg-utils manual). The following option is recognized:
‘file’
set the file name to use for the report; %p is expanded to the name of the program, %t is expanded to a timestamp, %% is expanded to a plain %
Errors in parsing the environment variable are not fatal, and will not appear in the report.
Você pode definir o -loglevel para warning ou error apenas para detectar erros. Pesquise na documentação para "nível de registro" para obter mais informações.