[FFmpeg-devel] -vf copy does transcode rather than copy
Paul B Mahol
onemda at gmail.com
Thu Oct 31 20:06:46 CET 2013
On 10/31/13, David Favor <david at davidfavor.com> wrote:
> Michael Bradshaw wrote:
>> On Thu, Oct 31, 2013 at 11:28 AM, David Favor <david at davidfavor.com>
>>> Maybe I'm missing something.
>>> The copy filter states...
>>> Copy the input source unchanged to the output. Mainly useful for
>>> testing purposes.
>>> Test case below shows input video bitrate is 938 kb/s output video
>>> is 836 kb/s
>>> and ffmpeg output shows libx264 is transcoding.
>> If you want to copy the stream without re-encoding it, don't you want
>> copy instead of -vf copy?
>> The copy filter just copies the input data to the output. But the input
>> decoded video frames (which it then copies to the output). Note that
>> and output here are referring to the filter graph, not the input/output
>> Data gets decoded -> Goes into filter graph -> "copy" filter just does a
>> straight copy of the data -> Goes out of the filter graph -> Gets encoded
>> by your command line parameters (and here it seems to be using defaults,
>> because you haven't specified any).
>> Someone please correct me if I'm wrong, though.
> -c:v copy maintains SAR + DAR info.
> -vf copy should allow (to me) a filter chain of something like...
> -vf copy,setdar=dar=0,setsar=sar=0
> which should accomplish the following...
> 1) copy the video stream (bit for bit) so no transcode
> 2) completely remove SAR + DAR to repair broken videos
> Bug is this....
> ffmpeg -i in.mp4 -c:a copy -vf copy out.mp4
> does a transcode instead of a copy... so it appear that -vf copy simply
> does not work.
> A work around for my situation is to override SAR + DAR in video stream
> via setting it in the container... via...
> ffmpeg -i in.mp4 -c:a copy -c:v copy -aspect 16:9 out.mp4
> And -vf copy still appears broken and should be fixed as there are other
> situations where video streams should be copied bit for bit.
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