[FFmpeg-user] -tune zerolatency has no effect with libx264

[Andy Furniss]

Examples from the streaming guide and encoding guide

https://trac.ffmpeg.org/wiki/StreamingGuide

use -tune zerolatency but it has no effect for me, also tested with -b:v ...

ph4[~]$ ffm -loglevel verbose -f v4l2 -s 640x480 -i /dev/video0 -vcodec 
libx264  -preset ultrafast -tune zerolatency  -f mpegts 
udp://239.255.0.1:1234
ffmpeg version N-68926-g0d0a905 Copyright (c) 2000-2015 the FFmpeg 
developers
   built on Jan  7 2015 00:17:43 with gcc 4.9.2 (GCC)
   configuration: --prefix=/usr --enable-opencl --enable-gpl 
--enable-nonfree --enable-libfdk-aac --enable-libmp3lame 
--enable-libx264 --enable-libx265 --enable-x11grab
   libavutil      54. 16.100 / 54. 16.100
   libavcodec     56. 19.100 / 56. 19.100
   libavformat    56. 18.100 / 56. 18.100
   libavdevice    56.  3.100 / 56.  3.100
   libavfilter     5.  6.100 /  5.  6.100
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  1.100 /  1.  1.100
   libpostproc    53.  3.100 / 53.  3.100
[video4linux2,v4l2 @ 0x2fbd6a0] fd:4 capabilities:85200001
Input #0, video4linux2,v4l2, from '/dev/video0':
   Duration: N/A, start: 14824.663826, bitrate: 55296 kb/s
     Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 640x480, 
55296 kb/s, 15 fps, 15 tbr, 1000k tbn, 1000k tbc
[graph 0 input from stream 0:0 @ 0x2f9f260] w:640 h:480 pixfmt:yuv420p 
tb:1/1000000 fr:15/1 sar:0/1 sws_param:flags=2
[libx264 @ 0x2fc0020] using cpu capabilities: MMX2 SSE2Fast LZCNT
[libx264 @ 0x2fc0020] profile Constrained Baseline, level 2.2
[mpegts @ 0x2fbef40] muxrate VBR, pcr every 1 pkts, sdt every 200, 
pat/pmt every 40 pkts
Output #0, mpegts, to 'udp://239.255.0.1:1234':
   Metadata:
     encoder         : Lavf56.18.100
     Stream #0:0: Video: h264 (libx264), yuv420p, 640x480, q=-1--1, 15 
fps, 90k tbn, 15 tbc
     Metadata:
       encoder         : Lavc56.19.100 libx264
Stream mapping:
   Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
frame=  551 fps= 15 q=21.0 Lsize=    7185kB time=00:00:36.73 
bitrate=1602.5kbits/s
video:6602kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB 
muxing overhead: 8.838692%
Input file #0 (/dev/video0):
   Input stream #0:0 (video): 551 packets read (253900800 bytes); 551 
frames decoded;
   Total: 551 packets (253900800 bytes) demuxed
Output file #0 (udp://239.255.0.1:1234):
   Output stream #0:0 (video): 551 frames encoded; 551 packets muxed 
(6760412 bytes);
   Total: 551 packets (6760412 bytes) muxed
[libx264 @ 0x2fc0020] frame I:3     Avg QP:19.00  size: 25500
[libx264 @ 0x2fc0020] frame P:548   Avg QP:21.25  size: 12197
[libx264 @ 0x2fc0020] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0x2fc0020] mb P  I16..4: 34.9%  0.0%  0.0%  P16..4: 65.0% 
0.0%  0.0%  0.0%  0.0%    skip: 0.1%
[libx264 @ 0x2fc0020] coded y,uvDC,uvAC intra: 73.5% 87.7% 55.3% inter: 
69.4% 81.1% 8.7%
[libx264 @ 0x2fc0020] i16 v,h,dc,p: 25% 20% 42% 14%
[libx264 @ 0x2fc0020] i8c dc,h,v,p: 47% 24% 21%  8%
[libx264 @ 0x2fc0020] kb/s:1472.32