ffmpeg常用命令参数

devices

show system devices/codecs/..

ffmpeg -devices  
ffmpeg -devices true -f dshow -i dummy  
ffmpeg -encoders  
ffmpeg -decoders

# read audio/video data from device  
ffmpeg -f dshow -i video="Integrated Camera" -f dshow -i audio=".."  
ffmpeg -f video4linux2 -i /dev/video0

video

video encoder

1	-c:v libx264 -v profile baseline -s 640x480 -b:v 512k -g 12

-c:v: codec of video
-b:v bitrate: bitrate of video(-b)
-s size: frame size(WxH)
-r rate: frame rate(HZ, e.g. 90000)
-g size: gop size(default 12)
-aspect aspect: aspect ratio (4:3, 16:9 or 1.3333, 1.7777)
-v profile baseline: codec profile
-keyint_min : minimum interval between IDR-frames(default 25)
-force_key_frames timestamps: force key frames at timestamps, e.g. -force_key_frames 0,2,4,6,8
-vn: diasbale video

if issues happen as below:
1). “ffmpeg Past duration 0.999992 too large”
due to uncertain framerates, fix it by setting -filter:v fps=(your framerate).

1	-filter:v fps=20

2). “[video input] too full or near too full”
This is because h264 encoder requires yuv420 input

1	-pix_fmt yuv420p

audio

1	-c:a aac -ar 44100 -ac 1 -ab 64k -strict -2 -f flv rtmp://localhost/hls/test

-c:a codec: codec of audio
-b:a bitrate: audio bitrate(-ab)
-ar rate: audio sampling rate(HZ, default 0)
-ac channels: audio channels(default 0)
-f fmt: force format
-an: disable audio

outputs

duplicate outputs. One to file, second to nginx-rtmp.

ffmpeg -i input1 -i input2 
	-acodec … -vcodec … output1 
	-acodec … -vcodec … output2 
	-acodec … -vcodec … output3
    
ffmpeg -i input 
	-s 1280x720 -acodec … -vcodec … output1 
	-s 640x480  -acodec … -vcodec … output2 
	-s 320x240  -acodec … -vcodec … output3

examples

ffmpeg examples

ffmpeg -re -i test.mp4 -c copy -f flv rtmp://localhost/hls/test0  
ffmpeg -re -i test.mp4 
	-pix_fmt yuv420p -c:v libx264 -vprofile baseline 
	-c:a aac -ar 44100 -ac 1 -strict -2 
	-f flv rtmp://localhost/hls/test1 
ffmpeg -f dshow -i video="Integrated Camera" -f dshow -i audio="Audio" 
    -pix_fmt yuv420p -c:v libx264 -vprofile baseline -s 640x480 -b:v 512k -filter:v fps=20 -g 10 
	-c:a aac -ar 44100 -ac 1 -b:a 64k -strict -2 
	-f flv rtmp://localhost/hls/test2

ffplay examples

1 2	ffplay -fflags nobuffer rtmp://localhost/hls/mystream -loglevel verbose ffplay -live_start_index -1 hls://localhost/app/mystream.m3u8

ffmpeg-usage