背景
ffmpeg 在转码 -ss accurate_seek 参数分析，是否可以精准的seek视频流。
构建测试素材
重新编码片源，设置片源gop间隔为10秒，帧率30fps，同时为每帧图像添加时间戳水印,素材时长为5分钟
转码命令：
ffmpeg -t 5:00 -i input.mp4 -vf “drawtext=fontsize=120:text=’%{pts:hms}’” -c:v libx264 -r 30 -g 300 -s 1280x720 -preset veryfast -crf 23 -an -f mp4 test.mp4 -y
ffmpeg -t 5:00 -i input.mp4 -vf "drawtext=fontsize=120:text='%{pts\:hms}'" -c:v libx264 -r 30 -g 300 -s 1280x720 -preset veryfast -crf 23 -an -f mp4 test.mp4 -y
校验：
ffprobe -i test.mp4 -of compact -show_frames -show_entries frame=key_frame,pkt_pts_time,pict_type,coded_picture_number | grep pict_type=I
ffprobe -i test.mp4 -of compact -show_frames -show_entries frame=key_frame,pkt_pts_time,pict_type,coded_picture_number | grep pict_type=I
查看关键帧信息
frame|key_frame=1|pkt_pts_time=0.000000|pict_type=I|coded_picture_number=0
frame|key_frame=1|pkt_pts_time=3.766667|pict_type=I|coded_picture_number=113
frame|key_frame=1|pkt_pts_time=13.433333|pict_type=I|coded_picture_number=403
frame|key_frame=1|pkt_pts_time=20.433333|pict_type=I|coded_picture_number=613
frame|key_frame=1|pkt_pts_time=29.033333|pict_type=I|coded_picture_number=871
frame|key_frame=1|pkt_pts_time=35.466667|pict_type=I|coded_picture_number=1064
frame|key_frame=1|pkt_pts_time=42.166667|pict_type=I|coded_picture_number=1265
frame|key_frame=1|pkt_pts_time=47.866667|pict_type=I|coded_picture_number=1436
frame|key_frame=1|pkt_pts_time=53.700000|pict_type=I|coded_picture_number=1611
frame|key_frame=1|pkt_pts_time=63.700000|pict_type=I|coded_picture_number=1911
frame|key_frame=1|pkt_pts_time=67.500000|pict_type=I|coded_picture_number=2025
frame|key_frame=1|pkt_pts_time=77.500000|pict_type=I|coded_picture_number=2325
frame|key_frame=1|pkt_pts_time=87.200000|pict_type=I|coded_picture_number=2616
frame|key_frame=1|pkt_pts_time=96.433333|pict_type=I|coded_picture_number=2893
frame|key_frame=1|pkt_pts_time=101.666667|pict_type=I|coded_picture_number=3050
frame|key_frame=1|pkt_pts_time=107.300000|pict_type=I|coded_picture_number=3219
frame|key_frame=1|pkt_pts_time=114.466667|pict_type=I|coded_picture_number=3434
frame|key_frame=1|pkt_pts_time=120.633333|pict_type=I|coded_picture_number=3619
frame|key_frame=1|pkt_pts_time=130.633333|pict_type=I|coded_picture_number=3919
frame|key_frame=1|pkt_pts_time=137.400000|pict_type=I|coded_picture_number=4122
frame|key_frame=1|pkt_pts_time=142.666667|pict_type=I|coded_picture_number=4280
frame|key_frame=1|pkt_pts_time=150.100000|pict_type=I|coded_picture_number=4503
测试
time ffmpeg -ss 145 -i test.mp4 -vframes 1 test.jpg -y; open test.jpg
time ffmpeg -accurate_seek -i test.mp4 -ss 145 -vframes 1 test.jpg -y; open test.jpg
感兴趣可以试试
参考：
https://trac.ffmpeg.org/wiki/Seeking