I'm using ffmpeg to extract one frame (as a jpeg) every five minutes from videos, and piping the output from the console to a text file in order to get the exact timestamps of the extracted frames.
The command I'm using is:
ffmpeg -i input.avi -ss 00:10:00 -vframes 10 -vf showinfo,fps=fps=1/300 %03d.jpg &> output.txt
Where -ss 00:10:00 lets me skip ahead 10 mins in the video before starting, and -vframes 10 lets me capture only the first 10 frames (1 frame per 5 mins).
This almost works fine except that the command outputs information for all frames, including those that were not written as a jpeg. Here's a three line sample output:
[Parsed_showinfo_0 @ 0x2219020] n:11427 pts:11429 pts_time:599.979 pos:48892180 fmt:yuv420p sar:1/1 s:640x480 i:P iskey:0 type:P checksum:6309A75D plane_checksum:[15A29007 1617E1FE D93A3549] mean:[146 125 153 ] stdev:[17.6 1.0 2.1 ]
[Parsed_showinfo_0 @ 0x2219020] n:11428 pts:11430 pts_time:600.031 pos:48898094 fmt:yuv420p sar:1/1 s:640x480 i:P iskey:0 type:B checksum:815D031A plane_checksum:[E004E973 E28CE2D5 F56636B4] mean:[146 125 153 ] stdev:[17.6 1.0 2.1 ]
[Parsed_showinfo_0 @ 0x2219020] n:11429 pts:11431 pts_time:600.084 pos:48892448 fmt:yuv420p sar:1/1 s:640x480 i:P iskey:0 type:P checksum:6CE2D3C5 plane_checksum:[E983BD86 38B9E198 93B13498] mean:[146 125 153 ] stdev:[17.6 1.0 2.1 ]
I would expect the middle line, with pts_time:600.031, to be the first frame extracted as an image, but have no way to distinguish it from the other frames either side, where images were not extracted.
Does anyone know of a way to resolve this?
Thank you!
You can use -vf showinfo for get frame information using ffmpeg . For example extracting frame when scene change and get time stamp for that particular frame.
ffmpeg -i image.mp4 -filter:v "select='gt(scene,0.1)',showinfo" -vsync 0 frames%05d.jpg >& output.txt
You will output similar like : [Parsed_showinfo_1 @ 0x25bf900] n: 0 pts: 119357 pts_time:9.95637 .... Our interest part is pts_time, Getting time use following command:
grep showinfo ffout | grep pts_time:[0-9.]* -o | grep '[0-9]*\.[0-9]*' -o > timestamps
You will get similar output:
9.95637
9.98974
15.0281
21.8016
28.208
28.4082
28.5083
In answer to my own question I've now found a workaround, though I'm not exactly sure how it works. By defining a select argument within -vf and also adding a vsync 0 parameter like so:
ffmpeg -i input.avi -vframes 10 -vf '[in]select=not(mod(n\,300*19.05))[s1];[s1]showinfo[out]' -vsync 0 %02d.jpg >& output.txt
...the function now returns the desired 10 frames only. Here's a sample stderr output of the first two frames:
[Parsed_showinfo_1 @ 0x21b1b60] n:0 pts:2 pts_time:0.104992 pos:10248 fmt:yuv420p sar:1/1 s:640x480 i:P iskey:1 type:I checksum:F6FDCFBF plane_checksum:[5FB6331C 9D9D7F99 44FB1D0A] mean:[183 126 155 ] stdev:[19.6 0.8 2.8 ]
frame= 1 fps=0.0 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=1.0 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.7 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.5 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.4 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.3 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.3 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.2 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
frame= 1 fps=0.2 q=4.1 size=N/A time=00:00:00.15 bitrate=N/A
[Parsed_showinfo_1 @ 0x21b1b60] n:1 pts:5717 pts_time:300.121 pos:24474150 fmt:yuv420p sar:1/1 s:640x480 i:P iskey:0 type:P checksum:BAECD030 plane_checksum:[F609470E 45F694CE 4BFCF445] mean:[148 126 152 ] stdev:[17.7 0.8 2.3 ]
frame= 2 fps=0.4 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.4 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.3 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.3 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.3 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.3 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.2 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.2 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
frame= 2 fps=0.2 q=2.1 size=N/A time=00:05:00.17 bitrate=N/A
Still unsure exactly why this works or why each frame= ... is replicated so many times in the output, but it seems to do the job!
Also, from the ffmpeg documentation of the "-ss" argument:
When used as an input option (before -i), seeks in this input file to position. Note the in most formats it is not possible to seek exactly, so ffmpeg will seek to the closest seek point before position.
So the frame that /should/ be returned is the one at n:11427.
