[FFmpeg-devel] -vf copy does transcode rather than copy

David Favor david at davidfavor.com
Fri Nov 1 14:01:16 CET 2013

Timothy Gu wrote:
> On Oct 31, 2013 12:53 PM, "Robert Krüger" <krueger at lesspain.de> wrote:
>> On Thu, Oct 31, 2013 at 7:38 PM, compn <tempn at twmi.rr.com> wrote:
>>> On Thu, 31 Oct 2013 11:35:34 -0600, Michael Bradshaw wrote:
>>>> On Thu, Oct 31, 2013 at 11:28 AM, David Favor <david at davidfavor.com>
> wrote:
>>>>> Maybe I'm missing something.
>>>>> The copy filter states...
>>>>>    Copy the input source unchanged to the output. Mainly useful for
>>>>> testing purposes.
>>> imo we shouldnt even document test/debug filters.
>>> it ONLY causes users to try them and have trouble...
>> No, there are people out there who are not ffmpeg devs who do debug
>> filter chains and know what they are doing and taking away the docs
>> would hurt them plus new developers who try to find their way around.
>> I'd prefer trying to make it clear in the text what they are for and
>> then live with the remaining misunderstandings. Just my 2c.
> Yeah. But in the doc debug filters/de/muxers/codecs should be clearly
> marked as such.

Agreed. I'm just working with filters for the first time... so when the
docs have a filter named 'copy' which says...

    Copy the input source unchanged to the output. Mainly useful for testing purposes.

I expected this to be true. Based on comments by people, I'd say
the documentation is far to simple.

In fact, I've yet to find an example where -vf copy works at all. In
every case, transcoding in some form occurs.

So... sounds like the copy filter documentation be expanded and maybe
add a few examples of an actual -vf copy operations along with what
video stream codecs -vf copy works with.

As someone else pointed out the video stream must be uncompressed for
-vf copy to work, so h264 streams will always fail to copy.

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