ffmpeg: Using the -SS option to process part of a video...

[Rekrul]

When I read the documentation and Google for examples, it all says that you can use -SS followed by a timestamp in the format of HH:MM:SS to have ffmpeg "quickly" seek to that portion of the file and start processing it there.

So if I enter the command;

ffmpeg -ss 00:03:00 -i input.mp4 output.mp4

It should quickly go through the video to the 3 minute mark, and start processing it from there.

Well, it processes it from the time I specify, but getting to that point is no faster than processing the file from the start.

In other words;

ffmpeg -ss 00:03:00 -i input.mp4 output.mp4

takes the same amount of time as;

ffmpeg -i input.mp4 output.mp4

The only difference being that the first one won't include the first three minutes in the output file.

What am I doing wrong?

[poisondeathray]

Well, it processes it from the time I specify, but getting to that point is no faster than processing the file from the start.

In other words;

ffmpeg -ss 00:03:00 -i input.mp4 output.mp4

takes the same amount of time as;

ffmpeg -i input.mp4 output.mp4

The only difference being that the first one won't include the first three minutes in the output file.

What am I doing wrong?

Nothing wrong.

Starting from the beginning is basically instantaneous (maybe a few ms latency) , but you want it faster than "instantaneous?"

To help you understand, compare with the the "slow" method , and then you will understand. The "slow" method decodes all frames up to that point. Put -ss after the -i, instead of before

ffmpeg -i input.mp4 -ss 00:03:00 output.mp4

[Rekrul]

Nothing wrong.

Starting from the beginning is basically instantaneous (maybe a few ms latency) , but you want it faster than "instantaneous?"

To help you understand, compare with the the "slow" method , and then you will understand. The "slow" method decodes all frames up to that point. Put -ss after the -i, instead of before

ffmpeg -i input.mp4 -ss 00:03:00 output.mp4

It seems I was following a bad example from the web, and I misunderstood what was happening.

As a test, I was trying to extract just one minute of video from the three minute mark to the four minute mark, and it was always processing four minutes. The problem was that I was using -t to specify the end time, rather than -to. So I was telling it to extract four minutes of video, but since I thought I had told it to stop at the four minute mark, it looked like it was just processing all the video up to that point.

I only briefly looked at the output videos and didn't notice that they were four minutes long. I was just testing the switches to see how they worked before trying to use them for what I really want to do, so when it looked like it wasn't working, I didn't go any further with it.

So long story short, it was me using the wrong switch.