CODEWITHSUNDEEP
ffmpeg
nathan wu
nathan wu

Reputation: 97

ffmpeg: cut video but getting the wrong length

I'm using ffmpeg to cut a video. Here is the input information:

    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 5113 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)

And this is the command I use:

    ffmpeg -y -ss 10 -t 5 -i test.mp4 -c copy output.mp4

But the output duration is about 9.66 seconds.

It worked when I removed the '-c copy' option or the input doesn't contain the 'tv, bt709' tag. But it's slower.

I wonder how I can use '-c copy' and get the right piece of video I need?

Upvotes: 6

Views: 6513

Answers (5)

Vova
Vova

Reputation: 1091

Check you file by ffprobe,

ffprobe -show_entries format <input_file>

Check the property, start_time, maybe in your case the property no a zero.

Upvotes: 0

ninhjs.dev
ninhjs.dev

Reputation: 8533

In my situation, I don't use -c copy but still receive an incorrect duration. Upon investigation, I found that it caused by "video chapters". So disable chapters by -map_chapters -1 will output the correct duration.

ffmpeg -ss 04:20 -to 04:41 -i "$input_file" -c:a aac -c:v h264_videotoolbox -b:v 29445k -map_chapters -1 "output.mp4"

-ss 04:20              : From
-to 04:41              : To
-i "$input_file"       : Input file
-c:a aac               : Set AAC codec for audio output
-c:v h264_videotoolbox : h264 hw encoder on Mac
-b:v 29445k            : Output video bitrate
-map_chapters -1       : Disable video chapters
"output.mp4"           : Output file

Upvotes: 13

Bora Savkar
Bora Savkar

Reputation: 75

just delete -c copy and you will get the exact cut.

"ffmpeg -y -ss 10 -t 5 -i test.mp4 output.mp4"

Upvotes: -1

Pullat Junaid
Pullat Junaid

Reputation: 3384

The first command will cut from 00:01:00 to 00:03:00 (in the original), using the faster seek.

The second command will cut from 00:01:00 to 00:02:00, as intended, using the slower seek.

The third command will cut from 00:01:00 to 00:02:00, as intended, using the faster seek.

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

ffmpeg -i video.mp4 -ss 00:01:00 -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

Full document enter link description here

Upvotes: 2

Momo
Momo

Reputation: 108

from the ffmpeg documentation:

-t duration (input/output) When used as an input option (before -i), limit the duration of data read from the input file.

When used as an output option (before an output url), stop writing the output after its duration reaches duration.

duration must be a time duration specification, see (ffmpeg-utils)the Time duration section in the ffmpeg-utils(1) manual.

Given this, if you want a 5 seconds video stream try to specify the duration you want to read from the input file (before the -i tag) and the duration you want from your final output file (before the output url)

Upvotes: 0

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