[FFmpeg-user] ffmpeg mux cause quality loss

[Wu, Mandy]

Yeah, that is I confused with. Mux should be lossless. I am thinking maybe I am wrong in the way of calculating PSNR. 
Is there any good PSNR calculation tool and reference? I am using the tool downloaded from http://www2.tkn.tu-berlin.de/research/evalvid/fw.html 


Thanks,
Mandy
-----Original Message-----
From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-bounces at ffmpeg.org] On Behalf Of Tom Evans
Sent: Friday, March 29, 2013 12:48 AM
To: FFmpeg user questions
Subject: Re: [FFmpeg-user] ffmpeg mux cause quality loss

On Thu, Mar 28, 2013 at 4:11 PM, Wu, Mandy <mandy.wu at intel.com> wrote:
> Hi,
> I used below command to mux H264 video and AAC audio to a MP4 container format:
> ffmpeg.exe -i video.h264 -i audio.aac -vcodec copy -acodec copy -absf 
> aac_adtstoasc output.mp4
>
> Then I found out value of PSNR of output.mp4 referring to video.h264 is only 30.62. It seems a pretty small number.
> Can someone advise how to use ffmpeg to mux H264 and AAC without much quality loss? Thanks a lot!
>

The command you quoted does not encode the video at all, it just copies it and muxes it to MP4, therefore the PSNR refers to the original video as well. I don't see how you can get any better quality than bit-for-bit identical with the source!

Cheers

Tom
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