为什么Nvenc编码器能提高解码速度？
为什么Nvenc编码器能提高解码速度？
提问于 2019-07-22 01:17:17
我试图提高解码h264视频到mp4视频的速度，使用c++中的Ffmpeg。我已经找到了一个cli命令，可以做到这一点，但是我仍然不完全理解在c++中复制它的命令，所以我希望你们能给我一个解释。
我发现的命令使用h264_nvenc编码器来提高使用GPU的速度。但是，我不明白为什么h264编码器会提高h264视频的解码速度(或者可能将编码提高到mp4帧)。谁能给我详细解释一下吗？
下面是我找到的cli命令：
ffmpeg -hwaccel cuvid -r 120 -i <input_file> -c:v h264_nvenc -preset fast -b:v 8M -vf scale=960:1080 -pix_fmt yuv420p <output_file> -y谢谢
编辑:带有选项"-c:v h264_nvenc“的命令日志
C:\Users\Shared\GolfTec\test>ffmpeg.exe -hwaccel cuvid -r 120 -i C:\\Users\\Shared\\GolfTec\\test\\raw0.h264 -c:v h264_nvenc -preset medium -b:v 8M -vf scale=960:1080 -pix_fmt yuv420p C:\\Users\\Shared\\GolfTec\\test\\video0.mp4 -y
ffmpeg version 3.4.1 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 7.2.0 (GCC)
configuration: --disable-static --enable-shared --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray
--enable-libfreetype --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy
--enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264
--enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis
--enable-cuda --enable-cuvid --enable-d3d11va --enable-nvenc
--enable-dxva2 --enable-avisynth --enable-libmfx
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
[h264 @ 0000027ecb2a6700] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, h264, from 'C:\\Users\\Shared\\GolfTec\\test\\raw0.h264':
Duration: N/A, bitrate: N/A
Stream #0:0: Video: h264 (CAVLC 4:4:4), yuv444p(progressive), 960x1080, 25 fps, 25 tbr, 1200k tbn, 50 tbc
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> h264 (h264_nvenc))
Press [q] to stop, [?] for help
Output #0, mp4, to 'C:\\Users\\Shared\\GolfTec\\test\\video0.mp4':
Metadata:
encoder : Lavf57.83.100
Stream #0:0: Video: h264 (h264_nvenc) (Main) (avc1 / 0x31637661), yuv420p, 960x1080, q=-1--1, 8000 kb/s, 120 fps, 15360 tbn, 120 tbc
Metadata:
encoder : Lavc57.107.100 h264_nvenc
Side data:
cpb: bitrate max/min/avg: 0/0/8000000 buffer size: 16000000 vbv_delay: -1
frame= 269 fps=261 q=25.0 Lsize= 2551kB time=00:00:02.23 bitrate=9356.5kbits/s speed=2.17x
video:2549kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.074325%没有选项"-c:v h264_nvenc“的命令日志
C:\Users\Shared\GolfTec\test>ffmpeg.exe -hwaccel cuvid -r 120 -i C:\\Users\\Shared\\GolfTec\\test\\raw0.h264 -preset medium -b:v 8M -vf scale=960:1080 -pix_fmt yuv420p C:\\Users\\Shared\\GolfTec\\test\\video0.mp4 -y
ffmpeg version 3.4.1 Copyright (c) 2000-2017 the FFmpeg developers
built with gcc 7.2.0 (GCC)
configuration: --disable-static --enable-shared --enable-gpl --enable-version3 --enable-sdl2 --enable-bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-cuda --enable-cuvid --enable-d3d11va --enable-nvenc --enable-dxva2 --enable-avisynth --enable-libmfx
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
[h264 @ 0000021e33556640] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, h264, from 'C:\\Users\\Shared\\GolfTec\\test\\raw0.h264':
Duration: N/A, bitrate: N/A
Stream #0:0: Video: h264 (CAVLC 4:4:4), yuv444p(progressive), 960x1080, 25 fps, 25 tbr, 1200k tbn, 50 tbc
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0000021e335589a0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0000021e335589a0] profile High, level 4.2
[libx264 @ 0000021e335589a0] 264 - core 152 r2851 ba24899 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=abr mbtree=1 bitrate=8000 ratetol=1.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, mp4, to 'C:\\Users\\Shared\\GolfTec\\test\\video0.mp4':
Metadata:
encoder : Lavf57.83.100
Stream #0:0: Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 960x1080, q=-1--1, 8000 kb/s, 120 fps, 15360 tbn, 120 tbc
Metadata:
encoder : Lavc57.107.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/8000000 buffer size: 0 vbv_delay: -1
frame= 269 fps= 39 q=-1.0 Lsize= 2279kB time=00:00:02.21 bitrate=8423.8kbits/s speed=0.32x
video:2277kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.119200%
[libx264 @ 0000021e335589a0] frame I:2 Avg QP:25.09 size: 16508
[libx264 @ 0000021e335589a0] frame P:193 Avg QP:23.94 size: 9094
[libx264 @ 0000021e335589a0] frame B:74 Avg QP:23.92 size: 7332
[libx264 @ 0000021e335589a0] consecutive B-frames: 62.8% 1.5% 0.0% 35.7%
[libx264 @ 0000021e335589a0] mb I I16..4: 38.2% 54.3% 7.6%
[libx264 @ 0000021e335589a0] mb P I16..4: 9.2% 11.8% 0.8% P16..4: 46.5% 3.4% 3.8% 0.0% 0.0% skip:24.5%
[libx264 @ 0000021e335589a0] mb B I16..4: 4.3% 3.7% 0.2% B16..8: 35.0% 1.5% 0.2% direct: 9.5% skip:45.5% L0:56.6% L1:40.9% BI: 2.5%
[libx264 @ 0000021e335589a0] final ratefactor: 19.31
[libx264 @ 0000021e335589a0] 8x8 transform intra:53.1% inter:88.1%
[libx264 @ 0000021e335589a0] coded y,uvDC,uvAC intra: 22.0% 41.2% 4.5% inter: 12.8% 39.4% 0.0%
[libx264 @ 0000021e335589a0] i16 v,h,dc,p: 18% 32% 19% 31%
[libx264 @ 0000021e335589a0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 14% 17% 54% 2% 3% 3% 4% 1% 2%
[libx264 @ 0000021e335589a0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11% 9% 63% 3% 4% 3% 3% 2% 2%
[libx264 @ 0000021e335589a0] i8c dc,h,v,p: 63% 23% 13% 1%
[libx264 @ 0000021e335589a0] Weighted P-Frames: Y:86.0% UV:64.8%
[libx264 @ 0000021e335589a0] ref P L0: 53.6% 8.3% 17.1% 11.4% 9.6%
[libx264 @ 0000021e335589a0] ref B L0: 58.9% 14.4% 26.6%
[libx264 @ 0000021e335589a0] ref B L1: 84.8% 15.2%
[libx264 @ 0000021e335589a0] kb/s:8317.64回答 1
Stack Overflow用户
回答已采纳
发布于 2019-07-22 08:37:54
好的，解码是一个更快的过程，所以通常是速率限制的进一步处理，主要是编码器，但也受到过滤器。通过运行s/w h264解码器的全速
ffmpeg -r 120 -i <input_file> -an -f null -添加过滤，以估计由于过滤器而导致的减速。
ffmpeg -r 120 -i <input_file> -vf scale=960:1080 -pix_fmt yuv420p -an -f null -之所以会发生这种情况，是因为ffmpeg以顺序的方式执行代码转换：
->解码->过滤器->将-> mux ->编码回步骤1.
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/57138181
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