[FFmpeg-user] Converting from h264(yuvj420p) to h264(yuv420p) without transcoding

[Wu-bin Zhen]

On Mon, Feb 11, 2013 at 5:33 PM, James Darnley <james.darnley at gmail.com>wrote:

> On 2013-02-11 23:10, Wu-bin Zhen wrote:
> > Hello ffmpeg,
> >
> > I have a weird device that only generates h264 video stream with
> yuv"J"420p
> > pixel format. Unfortunately the chrome browser does not support the pixel
> > format, so I have no choice but transcoding every frame from yuvj420p to
> > yuv420p. It costs a lot of time, and should be lose some quality because
> > each frame is going to be encoded again.
> >
> > I googled that there is an user modified the gpac MP4Box to manipulate
> VUI
> > property. I remember it is "fullrange" flag.
> >
> https://github.com/golgol7777/gpac/commit/913c0081d6882a713d66764c43827b6f3d05f925
> >
> > And it seems the trick is working for some users:
> > https://blendervse.wordpress.com/2012/04/02/waiving-the-fullrange-flag/
> >
> > My machine is not able to compile his gpac, and the old gpac has some
> > limitations. So I wonder if there is a "ffmpeg" way to change the pixel
> > format without transcoding every frame. I tried "-vcodec copy
> > -pix_fmt=yuv420p" options but it is not working, and the output file
> still
> > uses the yuv"J"420p pixel format.
>
> TO alter the fullrange flag (without encoding) someone would need to
> write a bitstream filter for ffmpeg, somewhat similar to the mp4toannexb
> filter.
>
>
Thanks. Then is there any open source tool on linux can do something like
this?


> Regardless, if that is true, that is a major issue with chrome.  It
> should play the video even if it doesn't know about the fullrange flag
> and wouldn't convert to RGB properly.  The only issue would be
> exaggerated contrast.
>
>
http://code.google.com/p/chromium/issues/detail?id=117368
The pixel format issue seems to be fixed few days ago. But I wonder if and
when google will push the fix. Right now I would not put too much hope on
something is not publicly available.


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