好象也没有什么参数吧
==== Available options: ====
Quality/bitrate control:
-q : Enables "target quality" mode.
is a floating-point number in 0...1 range.
-br : Specifies "target bitrate" mode.
is target bitrate in bits per second.
-cbr : Specifies "target bitrate (streaming)" mode.
is target bitrate in bits per second.
When neither of above quality/bitrate options is used,
the encoder defaults to equivalent of -q 0.5
Multipass encoding:
-2pass: Enables two-pass encoding mode.
Note that two-pass more requires a physical file as input,
rather than stdin.
-2passperiod : Overrides two-pass encoding bitrate averaging period,
: in milliseconds.
: Specify zero to use least restrictive value possible (default).
Advanced features / troubleshooting:
-lc : Forces use of LC AAC profile (HE features disabled)
-he : Forces use of HE AAC profile (HEv2 features disabled)
-hev2 : Forces use of HEv2 AAC profile
Note that the above switches (-lc, -he, -hev2) should not be
used; optimal AAC profile is automatically determined from
quality/bitrate settings when no override is specified.
-hinttrack Generates an RTP hint track in output MP4 file.
-ignorelength : Ignores length signaled by WAV headers of input file.
Useful for certain frontends using stdin.