bash ffmpeg 捕获当前帧并覆盖图像输出文件
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ffmpeg capture current frame and overwrite the image output file
提问by Xianlin
I am trying to extract the image file from a RTSP stream url every second (could be every 1 min also) and overwrite this image file.
我正在尝试每秒从 RTSP 流 url 中提取图像文件（也可能是每 1 分钟一次）并覆盖此图像文件。
my below code works but it outputs to multiple image jpg files: img1.jpg, img2.jpg, img3.jpg...
我下面的代码有效，但它输出到多个图像 jpg 文件： img1.jpg, img2.jpg, img3.jpg...
ffmpeg -i rtsp://IP_ADDRESS/live.sdp -f image2 -r 1 img%01d.jpg
How to use ffmpeg or perhaps bash scripts in Linux to overwrite the same image file while continuously extract the image at a NOT high frequecy, say 1 min or 10 sec?
如何在 Linux 中使用 ffmpeg 或 bash 脚本覆盖相同的图像文件，同时以不高的频率连续提取图像，比如 1 分钟或 10 秒？
回答by pragnesh
Following command line should work for you.
以下命令行应该适合您。
ffmpeg -i rtsp://IP_ADDRESS/live.sdp -f image2 -updatefirst 1 img.jpg
回答by Pau Coma Ramirez
To elaborate a bit on the already accepted answerfrom pragnesh,
FFmpeg
FFmpeg
As stated in the ffmpeg documentation: ffmpeg command line options are specified as
如ffmpeg 文档中所述：ffmpeg 命令行选项指定为
ffmpeg [global_options] {[input_options] -i input_file} ... {[output_options] output_file} ...
ffmpeg [global_options] {[input_options] -i input_file} ... {[output_options] output_file} ...
So
所以
ffmpeg -i rtsp://<rtsp_source_addr> -f image2 -update 1 img.jpg
ffmpeg -i rtsp://<rtsp_source_addr> -f image2 -update 1 img.jpg
Uses output option-f image2 , force output format to image2 format, as part of the muxer stage.
使用输出选项-f image2 ，强制输出格式为 image2 格式，作为复用器阶段的一部分。
Note that in ffmpeg, if the output file name specifies an image format the image2 muxer will be used by default, so the command could be shortened to:
ffmpeg -i rtsp://<rtsp_source_addr> -update 1 img.jpg
请注意，在 ffmpeg 中，如果输出文件名指定了图像格式，则默认情况下将使用 image2 muxer，因此该命令可以缩短为：
ffmpeg -i rtsp://<rtsp_source_addr> -update 1 img.jpg
The image2 format muxerexpects a filename pattern, such as img%01d.jpgto produce a sequentially numbered series of files. If the updateoptionis set to 1, the filename will be interpreted as just a filename, not a pattern, thereby overwriting the same file.
的图像2格式复用器期望的文件名模式，例如img%01d.jpg，以产生按顺序编号的一系列文件。如果更新选项设置为 1，文件名将被解释为只是一个文件名，而不是一个模式，从而覆盖同一个文件。
Using the -r, set frame rate, video optionworks, but generated me a whole lot of dropping frame messages which was bugging me.
使用-r，设置帧速率，视频选项有效，但给我带来了很多丢帧消息，这让我很烦恼。
Thanks to another answer on the same topic, I found the fps Video Filterto do a better job.
感谢同一主题的另一个答案，我发现fps 视频过滤器做得更好。
So my version of the working command is
所以我的工作命令版本是
ffmpeg -i rtsp://<rtsp_source_addr> -vf fps=fps=1/20 -update 1 img.jpg
For some reason still unkown to me the minimum framerate I can achieve from my feed is 1/20 or 0.05.
出于某种原因，我仍然不知道我可以从我的提要中获得的最低帧率是 1/20 或 0.05。
There also exists the video filter thumbnail, which selects an image from a series of frames but this is more processing intensive and therefore I would not recommend it.
还有视频过滤器缩略图，它从一系列帧中选择一个图像，但这需要更多的处理，因此我不推荐它。
Most of this and more I found on the FFMpeg Online Documentation
我在FFMpeg 在线文档中找到的大部分内容和更多内容
AVconv
AV转换
For those of you who use avconv it is very similar. They are after all forks of what was once a common library. The AVconv image2 documentation is found here.
对于那些使用 avconv 的人来说，它非常相似。毕竟，它们是曾经是公共图书馆的分支。该AVconv图像2文档可以在这里找到。
avconv -i rtsp://<rtsp_source_addr> -vf fps=fps=1/20 -update 1 img.jpg
avconv -i rtsp://<rtsp_source_addr> -vf fps=fps=1/20 -update 1 img.jpg
As Xianlin pointed out there may be a couple other interesting options to use:
正如 Xianlin 指出的那样，可能还有其他一些有趣的选项可供使用：
-an: Disables audio recording.
-an：禁用录音。
- Found in Audio Options Section
- 在音频选项部分找到
-r< fps >: sets frame rate
-r < fps >: 设置帧率
- Found in the Video Options Section
- used as an output option is actually a a substitute for the fps filter
leading to an alternate version :
导致替代版本：
avconv -i rtsp://<rtsp_source_addr> -r 1/20 -an -update 1 img.jpg
avconv -i rtsp://<rtsp_source_addr> -r 1/20 -an -update 1 img.jpg
Hope it helps understand for possible further tweaking ;)
希望它有助于理解可能的进一步调整；)
回答by bleekerk
I couldn't get the option -update working to overwrite the .jpg. Doing some experiments resulted in a working solution (at least for me) with the option -y at the end (upper-case is not working). I also needed http:// instead of rstp:// for this camera.
我无法使用选项 -update 来覆盖 .jpg。做一些实验得到了一个可行的解决方案（至少对我来说），最后带有 -y 选项（大写不起作用）。对于这台相机，我还需要 http:// 而不是 rstp://。
ffmpeg -i http://xx:[email protected]:yyy/snapshot.cgi /tmp/Capture2.jpg -y
ffmpeg -i http://xx:[email protected]:yyy/snapshot.cgi /tmp/Capture2.jpg -y
回答by Kokkie
Grab a snapshot from an RTSP video stream every 10 seconds.
每 10 秒从 RTSP 视频流中获取快照。
#!/bin/bash
#fetch-snapshots.sh
url='rtsp://IP_ADDRESS/live.sdp'
avconv -i $url -r 0.1 -vsync 1 -qscale 1 -f image2 images%09d.jpg
-r rate set frame rate to 0.1 frames a second (this equals to 1 frame every 10 seconds). Thanks to westonruter, see https://gist.github.com/westonruter/4508842
-r rate 将帧速率设置为每秒 0.1 帧（这等于每 10 秒 1 帧）。感谢 westonruter，参见https://gist.github.com/westonruter/4508842
Furthermore have a look at FFMPEG: Extracting 20 images from a video of variable length
