MathewSachin/Captura

Trim tool FFmpeg error on Windows (Unknown decoder 'copy')

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#410 opened on May 18, 2019

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bughelp wanted

Description

I found a bug in order of args in trim tool:

ARGS:
-------------
-ss 00:00:00.0000000 -to 00:01:00.0000000 -acodec copy -i "C:\rec.webm"  "C:\trimmed_rec.webm"

OUTPUT:
-------------
ffmpeg version N-93880-gc3458f06f4 Copyright (c) 2000-2019 the FFmpeg developers
  built with gcc 8.3.1 (GCC) 20190414
... bla-bla
Unknown decoder 'copy'

By little bit of googling, I found the solution lists.ffmpeg.org/why_this_ffmpeg_shell_command_is_wrong:

So, this is okay:
ffmpeg -i input -c:v copy output
This is not okay:
ffmpeg -c:v copy -i input output

So it's true, direct command like this works fine: ffmpeg -i "C:\rec.webm" -ss 00:00:00.0000000 -to 00:01:00.0000000 -acodec copy "C:\trimmed_rec.webm"

Desktop:

  • OS: Windows 10 x64 v1803
  • RAM: 8GB
  • CPU: i5 2.6GHz
  • Graphic Card: GTX760 2GB

Contributor guide

Tech stack
shell
Domain
cli
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
None
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
90
Research direction
The issue identifies that FFmpeg arguments are in wrong order: ' ss ... to ... acodec copy i input' should be ' i input ss ... to ... acodec copy'. The fix is to reorder the arguments in the trim tool code. The relevant code likely constructs FFmpeg command line. The FFmpeg mailing list link provides explanation. Check the code in the repository that builds FFmpeg command arguments (likely in a C# file). Change the order to place ' i' before codec options.