For #1659, #307, add opus and ffmpeg codec library

[winlinvip]

libopus, which is rarely updated, is placed as a compressed file in 3rdparty.
ffmpeg, on the other hand, needs to be updated. Like st, its code is placed in 3rdparty and compiled into a library.

---

TRANS_BY_GPT3

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (feature/codec@2da4e0a). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff                @@
##             feature/codec    #1661   +/-   ##
================================================
  Coverage                 ?   65.63%           
================================================
  Files                    ?      108           
  Lines                    ?    42587           
  Branches                 ?        0           
================================================
  Hits                     ?    27954           
  Misses                   ?    14633           
  Partials                 ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data'

Translated to English:

Δ = absolute <relative> (impact), ø = not affected, ? = missing data'
Powered by Codecov. Last update 2da4e0a...602a478. Read the comment docs.

TRANS_BY_GPT3

[winlinvip]

SRS that supports WebRTC, 19MB. Mainly added a few static libraries:
libsrtp2.a 166KB
libopus.a 3.5MB
libavcodec.a 12MB
libavutil.a 3.6MB
libswresample.a 649KB

SRS that does not support WebRTC, 9.8MB, dependent libraries include:
libcrypto.a 4.8MB
libssl.a 747KB
libst.a 132KB

After compression, the original FFMPEG 4.2 source code is 10MB, and after decompression, it is 81MB. After trimming, the FFMPEG code is 8.9MB.

TRANS_BY_GPT3

[winlinvip]

FFMPEG is under the LGPL license. It will support dynamic library linking in the future, with static library linking as the default option.

TRANS_BY_GPT3