4 Changing the video resolution (scaling).This is why your video player displays frozen or black frames: the necessary data to represent the first portion of your video isn’t included in the file. If you use this command and try to play your output clip, you may notice that the clip starts frozen, or with black frames in the beginning.īy stream copying with all-frame seeking we have removed the reference Key frames which came before our first frame. This means that your output clip will start with the nearest frame to 30 seconds even if it is a predicted frame.

It is also a stream copy, but considers all frames (including Predicted frames) when performing a seek. This method uses all-frame seeking, also known as “output seeking” by FFmpeg users. Image.png copy模式的不良使用方式 All-Frame SeekingĪ slightly slower and more accurate method of video cutting would be the following: ffmpeg -i input_vid.mp4 -ss 30 -t 60 -c copy output_clip.mp4 'stream copy' means ' duplicate the stream without modification' 示例分析

This feature may be useful for some users who don’t care about frame accuracy It also is a stream copy meaning that the encoded data extracted from the original video is taken directly without decoding and then re-encoding. This method is so fast because it uses Key frames when performing seek, and there are far fewer Key frames than Predicted frames. The fastest way to extract a portion of video from a larger video (with a 60 second clip starting 30 seconds in) would be the following: ffmpeg -ss 30 -i input_vid.mp4 -t 60 -c copy output_clip.mp4 However, it might not work in some cases because of many factors.Īpplying filters is obviously also impossible, since filters work on uncompressed data. Since there is no decoding or encoding, it is very fast and there is no quality loss. | input | demuxer | encoded data | muxer | output | The diagram above will, in this case, simplify to this: _ _ _ It is useful for changing the container format or modifying container-level metadata. It makes ffmpeg omit the decoding and encoding step for the specified stream, so it does only demuxing and muxing. Stream copy is a mode selected by supplying the copy parameter to the -codec option.

Ffmpeg copy parameter