[FFmpeg-devel] [PATCH] lavc/flacdec: Add frame CRC calculation

[Michael Niedermayer]

On Sun, Feb 17, 2013 at 12:09:29AM -0300, James Almer wrote:
> On 16/02/13 11:35 PM, Michael Niedermayer wrote:
> > On Sun, Feb 17, 2013 at 03:30:54AM +0100, Michael Niedermayer wrote:
> >> On Sat, Feb 16, 2013 at 10:43:28PM -0300, James Almer wrote:
> >>> On 16/02/13 9:30 PM, Michael Niedermayer wrote:
> >>>> On Sat, Feb 16, 2013 at 08:56:18PM -0300, James Almer wrote:
> >>>>> On 16/02/13 8:45 PM, Michael Niedermayer wrote:
> >>>>>> On Sat, Feb 16, 2013 at 06:07:49AM -0300, James Almer wrote:
> >>>>>>> Fixes ticket #2266
> >>>>>>>
> >>>>>>> Signed-off-by: James Almer <jamrial at gmail.com>
> >>>>>>
> >>
> >>>>>> does this improve or worsen the way damaged files sound ?
> >>
> >> ping
> > 
> > to clarify
> > 1. damage a flac file
> > 2. listen to it with and without the patch
> > 3. describe the results of how it sounds
> > 
> > we want the output to sound best
> > we want to inform the user of damaged non lossless data
> > we want to make it possible for the user to enable / disable hard CRC
> > checks that discard data
> 
> I wrote a reply, saying that it would depend on how damaged is the file.

you didnt indicate if this was based on guessing or testing which is
why i asked


> 
> Also, I'm not sure how to do considerable damage to a file while avoiding 
> triggering the many other checks made on it (subframe padding check, qlevel 
> check, etc).
> Using an hex editor i managed to change some random bytes to trigger crc 
> errors, but as i said in my other reply, the difference was practically 
> inaudible without the patch (With it, the dropped frame/s were somewhat 
> noticeable since the audio skips).

from this it would seem better not to drop frames with damaged CRCs by
default


> 
> Afaik, dropping the frame or not on crc checks currently depends on the 
> decoder and not the user.

the user can change the options

i think the check should be
if(err & (AV_EF_CRCCHECK|AV_EF_COMPLIANT))

and we should think about loosing AV_EF_CRCCHECK from the default
flags

[...]
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