[mythtv] [mythtv-commits] Ticket #6986: max CPUs setting for Multithreading ffmpeg h264 has no affect.

John reidjr at btconnect.com
Sun Sep 6 07:05:56 UTC 2009

MythTV wrote:
> #6986: max CPUs setting for Multithreading ffmpeg h264 has no affect.
> -----------------------------------+----------------------------------------
>  Reporter:  reidjr_at_lineone_net  |        Owner:  ijr    
>      Type:  defect                 |       Status:  closed 
>  Priority:  major                  |    Milestone:         
> Component:  MythTV - General       |      Version:  head   
>  Severity:  medium                 |   Resolution:  invalid
>   Mlocked:  0                      |  
> -----------------------------------+----------------------------------------
> Comment(by anonymous):
>  Replying to [comment:1 janne]:
>  > slice based multi threading requires disabled or not slice spanning loop
>  filter.
>  >
>  > so this is a known limitation and I close this as feature request
>  without patch. it will be fixed when frame based multithreading is merged
>  to ffmpeg.
>  Thanks for the clarification. Patch to disable the loop filter is attached
>  to #4653
I spent some time checking if this was a known issue, and trying to 
backtrack through versions to see where it "stopped working". I had 
obviously never noticed that you needed to disable loop filter to use 
multi threaded, as I have always needed both. It wasn't in the mailing 
archives, but now I have the magic key words "slice based multi 
threading" Google puts it in the first few hits.

Strangely I found that loop filter disabled on a single core made no difference, and multi threading appeared to increase  the overall usage. As I am sure that on a single core disabling the loop filter used to reduce the cpu load by about 40%, as my first attempts with the skip loop patch was on a 3200+ Athlon.  Any I idea why this is, has the underlying ffmpeg loop filter code improved significantly, or why is disabling the loop filter making little or no difference ?

I guess theres still no chance of disabling the loop filter by default with a 1 line patch ? 

Thanks again. 

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