我目前正在通过 macOS 上的 Blackmagic decklink 卡捕捉视频。我的音频和视频不同步。音频提前了大约一秒钟。由于编码延迟，我怀疑视频速度较慢。我的解决方案是使用 ffmpeg adelay 过滤器来延迟音频。我最初在命令中添加了一个 -af "adelay=1000|1000" 以将音频延迟 1000 毫秒，但我发现这个音频过滤器什么也没做。因此，我尝试构建一个 complex_filter，但失败了。我的命令产生了太多流，ffmpeg 无法将它们路由到正确的 rtp 端点。那么延迟音频的最佳方法是什么，我可以选择哪些流映射到 rtp 端点？
ffmpeg \
-format_code 23ps \
-f decklink \
-i "DeckLink HD Extreme 3" \
-filter_complex "[0:a] adelay=2s|2s [delayed]" \
-map [delayed] -map 0:v \
-r 24 \
-g 1 \
-s 1920x1080 \
-quality realtime \
-speed 8 \
-threads 8 \
-row-mt 1 \
-tile-columns 2 \
-frame-parallel 1 \
-qmin 30 \
-qmax 35 \
-b:v 2000k \
-pix_fmt yuv420p \
-c:v libvpx-vp9 \
-strict experimental \
-an -f rtp rtp://myurl.com:5004?pkt_size=1300 \
-c:a libopus \
-b:a 128k \
-vn -f rtp rtp://myurl.com:5002?pkt_size=1300
在运行命令时添加完整的日志，没有任何延迟：
-filter_complex "[0:a] adelay=2s|2s [delayed]" \
-map [delayed] -map 0:v \
ffmpeg version N-97362-g889ad93c88 Copyright (c) 2000-2020 the FFmpeg developers
built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
configuration: --prefix=/usr/local --pkg-config-flags=--static --extra-cflags='-fno-stack-check -I/Users/admin/Documents/ffmpeg_build/include -I/Users/admin/Documents/BDS/Mac/include' --extra-ldflags=-L/Users/admin/Documents/ffmpeg_build/lib --extra-libs='-lpthread -lm' --bindir=/Users/admin/Documents/ffmpeg_build/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree --enable-decklink
libavutil 56. 42.102 / 56. 42.102
libavcodec 58. 80.100 / 58. 80.100
libavformat 58. 42.100 / 58. 42.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 77.101 / 7. 77.101
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100
[decklink @ 0x7fcfb2000000] Found Decklink mode 1920 x 1080 with rate 23.98
[decklink @ 0x7fcfb2000000] Frame received (#2) - No input signal detected - Frames dropped 1
Guessed Channel Layout for Input Stream #0.0 : stereo
Input #0, decklink, from 'DeckLink HD Extreme 3':
Duration: N/A, start: 0.000000, bitrate: 797002 kb/s
Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Stream #0:1: Video: rawvideo (UYVY / 0x59565955), uyvy422(progressive), 1920x1080, 795466 kb/s, 23.98 tbr, 1000k tbn, 1000k tbc
[decklink @ 0x7fcfb2000000] Frame received (#3) - Input returned - Frames dropped 2
Stream mapping:
Stream #0:1 -> #0:0 (rawvideo (native) -> vp9 (libvpx-vp9))
Stream #0:0 -> #1:0 (pcm_s16le (native) -> opus (libopus))
Press [q] to stop, [?] for help
[libvpx-vp9 @ 0x7fcfb180d200] v1.8.2
Output #0, rtp, to 'rtp://myurl.com.com:5004?pkt_size=1300':
Metadata:
encoder : Lavf58.42.100
Stream #0:0: Video: vp9 (libvpx-vp9), yuv420p, 1920x1080, q=30-35, 2000 kb/s, 24 fps, 90k tbn, 24 tbc
Metadata:
encoder : Lavc58.80.100 libvpx-vp9
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
Output #1, rtp, to 'rtp://myrul.com:5002?pkt_size=1300':
Metadata:
encoder : Lavf58.42.100
Stream #1:0: Audio: opus (libopus), 48000 Hz, stereo, s16, 128 kb/s
Metadata:
encoder : Lavc58.80.100 libopus
SDP:
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
t=0 0
a=tool:libavformat 58.42.100
m=video 5004 RTP/AVP 96
c=IN IP4 54.183.58.143
b=AS:2000
a=rtpmap:96 VP9/90000
m=audio 5002 RTP/AVP 97
c=IN IP4 54.183.58.143
b=AS:128
a=rtpmap:97 opus/48000/2
a=fmtp:97 sprop-stereo=1
frame= 434 fps= 24 q=0.0 size= 37063kB time=00:00:18.09 bitrate=16780.7kbits/s speed=1.01x