[FFmpeg-user] Multithreaded multioutput problem

[Marton Balint]

On Mon, 20 Apr 2015, Deron wrote:

> On 4/20/15 4:22 PM, Marton Balint wrote:
>> 
>> On Mon, 20 Apr 2015, Deron wrote:
>> 
>>> On 4/20/15 1:48 PM, Marton Balint wrote:
>>>> On Mon, 20 Apr 2015, Deron wrote:
>>>> 
>>>>> Another user has contacted me with the exact same problem hoping that I 
>>>>> stumbled on a solution for the below problem. I did not, so I am adding 
>>>>> some more extensive log output in hopes that someone might recongize the 
>>>>> source of the problem.
>>>>> 
>>>> 
>>>> I have also experienced this problem. Depending on your use case you can 
>>>> face a similar situation with only one input and one output as well and a 
>>>> few cores. There is no buffering between the various stages of the ffmpeg 
>>>> encoder/filter/decoder pipeline, so even if the stages by themselves are 
>>>> multi threaded, you won't be able to scale up, because passing data 
>>>> between the stages is done in a single thread.
>>>> 
>>>> Or at least that is what I think is going on. So as far as I know you can 
>>>> only scale up properly by running multiple ffmpeg instances. E.g: create 
>>>> a multicast and encode that.
>>>> 
>>>> Regards,
>>>> Marton
>>> 
>>> 
>>> What would be the best way to solve this then? I'm not sure I understand 
>>> what you mean by multicast. Having multiple ffmpeg's decoding the same 
>>> original mpegts input would be pretty slow.
>> 
>> If that overhead is unacceptable, then I don't see any other way. You wrote 
>> you had plenty of free CPU :)
>
> Speaking of CPU and having been away from the problem for many weeks, I 
> forget about the important part. The encoding process for the data runs at 
> better than real time (nearly 2x) when pulling from a file instead of the 
> /dvb device. So I don't think that this is thread bound for me but something 
> else.
>
> I'm still missing a piece of the puzzle. Something else is causing me grief.
>

In that case have you tried using the threaded input read support of 
ffmpeg? You have to specify more than one inputs (add an extra dummy 
input source) and play with -thread_queue_size option.

Regards,
Marton