google-chrome - 谷歌浏览器中这些 http-livestream 伪影的原因可能是什么？

Question

这是 http-livestream 设置:服务器正在使用 DASH 协议(protocol)和 h264 编码运行 ffmpeg。客户端正在使用 Dash.js。分辨率固定为 1920x1080，具有 24 位深度和 60hz。
伪影(下图)仅在视频的最后一行位于 chrome 视口(viewport)内时出现(因此，如果页面向上滚动，它就会消失)。它表现为向下拉伸(stretch)中心行像素，并且似乎只影响某些颜色 channel 。
我尝试更改比特率，并从源代码中删除最后一行，认为问题可能出在服务器端，没有任何影响。问题取决于视口(viewport)中的位置这一事实使我怀疑 chrome 本身存在故障。
我还尝试在 chrome:\flags 中强制关闭硬件解码，但这并不能解决问题。
请就可能导致此问题的原因提交您的假设。谢谢。


更新#1
这是 ffmpeg 命令行和日志:

export DISPLAY=:0 && ffmpeg -f x11grab -framerate 60 -video_size 1920x1080 -i :0.0+0,0 -draw_mouse 0 -f dash -utc_timing_url https://time.akamai.com/?iso -streaming 1 -seg_duration 2 -frag_duration 0.033 -fflags nobuffer -fflags flush_packets -c:v h264 -preset ultrafast data/stream.mpd

和日志:

ffmpeg version 4.2.4-1ubuntu0.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.3.0-10ubuntu2)
  configuration: --prefix=/usr --extra-version=1ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
[x11grab @ 0x561ca34b9980] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, x11grab, from ':0.0+0,0':
  Duration: N/A, start: 1618941693.853256, bitrate: N/A
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080, 60 fps, 1000k tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0x561ca34c5300] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 AVX512
[libx264 @ 0x561ca34c5300] profile High 4:4:4 Predictive, level 4.2, 4:4:4 8-bit
[libx264 @ 0x561ca34c5300] 264 - core 155 r2917 0a84d98 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=1 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=6 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250 keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
[dash @ 0x561ca34c3740] No bit rate set for stream 0
[dash @ 0x561ca34c3740] Opening 'data/init-stream0.m4s' for writing
Output #0, dash, to 'data/stream.mpd':
  Metadata:
    encoder         : Lavf58.29.100
    Stream #0:0: Video: h264 (libx264), yuv444p, 1920x1080, q=-1--1, 60 fps, 15360 tbn, 60 tbc
    Metadata:
      encoder         : Lavc58.54.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
[dash @ 0x561ca34c3740] Opening 'data/chunk-stream0-00001.m4s.tmp' for writing
frame=   34 fps=0.0 q=15.0 size=N/A time=00:00:00.43 bitrate=N/A dup=5 drop=0 speed=0.836x    
frame=   65 fps= 64 q=15.0 size=N/A time=00:00:00.95 bitrate=N/A dup=5 drop=0 speed=0.929x    
frame=   96 fps= 62 q=15.0 size=N/A time=00:00:01.46 bitrate=N/A dup=5 drop=2 speed=0.955x    
frame=  126 fps= 62 q=15.0 size=N/A time=00:00:01.96 bitrate=N/A dup=5 drop=3 speed=0.962x    
frame=  157 fps= 62 q=15.0 size=N/A time=00:00:02.48 bitrate=N/A dup=5 drop=3 speed=0.973x    
frame=  188 fps= 61 q=15.0 size=N/A time=00:00:03.00 bitrate=N/A dup=5 drop=3 speed=0.98x    
frame=  217 fps= 61 q=15.0 size=N/A time=00:00:03.48 bitrate=N/A dup=5 drop=3 speed=0.977x    
frame=  247 fps= 61 q=15.0 size=N/A time=00:00:03.98 bitrate=N/A dup=6 drop=3 speed=0.976x    
[dash @ 0x561ca34c3740] Opening 'data/stream.mpd.tmp' for writing
[dash @ 0x561ca34c3740] Opening 'data/chunk-stream0-00002.m4s.tmp' for writing
frame=  279 fps= 61 q=15.0 size=N/A t

Answer 1

添加 -vf format=yuv420p YUV 4:2:0 chroma subsampling 的输出选项.这是唯一广泛支持的 H.264 色度二次采样方案。
您的输入像素格式是 bgr0。你的输出是 yuv444p。 ffmpeg 尝试尽可能多地保留保真度，因此它会自动将其转换为所选编码器支持的最类似于源的像素格式。在这种情况下，它是不受普遍支持的 yuv444p (YUV 4:4:4)。