Black frames at beginning of video file when file cut

Question

I use ffmpeg to cut a video file. The format i use is this:

ffmpeg -i input.avi -ss 00:06:30 -to 00:07:15 -c copy output.avi

Unfortunately this leaves some black frames in the beginning of my output video, so i lose certain parts of the video. In one video i tried, this went on for one second, in another, the black frames lasted 4 seconds.

The funny thing is that when i used the same command, exactly the same amount of black frame exists for the same video. Meaning, no matter how many times i did this for my second video, in all outputs, the output video will be blank for the first 4 seconds!

The sound works great though!

Here are some other command formats i tried and did NOT work:

ffmpeg -ss 00:01:00 -i video.mp4 -to 00:02:00 -c copy cut.mp4
ffmpeg -ss 00:01:00 -i video.mp4 -to 00:02:00 -c copy -copyts cut.mp4

I thout i found my solution with the command i used, but then this problem occured

EDIT: I figured out that if i don't use the -c copy flag, then i do not have the black frames:

ffmpeg -i input.avi -ss 00:06:30 -to 00:07:15 output.avi

However, with this method, the quality of my output video is significantly lower than the input video, or the output video from the previous methods. So i am back at square one.

Answer 1

Make sure that you are using a recent version of ffmpeg by downloading a static build, for example. There have been some major changes a while ago which affect how stream cutting works.

Here's the important difference between the commands that you ran:

• When specifying -c copy, ffmpeg will cut the video without modifying the actual bitstream. In other words, it will take the frames as-is and copy them to the output file. In some cases (simply put, when the starting time does not correspond to an I-frame), ffmpeg needs to include some more frames that are needed to properly decode the first frame to be displayed. Those will get a negative timestamp, so they shouldn't be shown.

• When you leave out -c copy, ffmpeg will re-encode the video with whatever encoder (mpeg4, libx264, ...) is the default for the chosen output format (AVI or MP4 in your case). These encoders may have default quality or bitrate settings that make the output look bad. When re-encoding, you should therefore know what target quality you want to set.

If cutting with stream copying does not work for you, and if you have to re-encode the video, you may as well use a recent and efficient video codec (H.264) and container (MP4), and copy the audio stream:

ffmpeg -ss 00:10:45 -i input.avi -c:v libx264 -crf 18 -to 00:11:45 -c:a copy output.mp4

Here, the CRF option controls the output quality. Values between 18 and 28 are "normal", lower values are better. The -ss option can be an input option (i.e., one that appears before -i) which makes everything faster.

For more information, read the Seeking guide on the FFmpeg Wiki.

Answer 2

For anyone having the same problem, i finally managed to solve it with this:

ffmpeg -i input.avi -qscale 0 -ss 00:10:45 -to 00:11:45 output.avi