[FFmpeg-user] Asynchronous overlays

[Baptiste Coudurier]

Hi,

On 05/18/2011 09:24 AM, Alexandre Ferrieux wrote:
> Hello,
> 
> I'd like to put side-by-side two video sources (with the overlay
> filter), with a completely asynchronous/decoupled scheme. Indeed my two
> video sources have varied and unstable frame rates, and in a naive setup
> of the overlay filter, ffmpeg insists on fetching a frame from each one
> for every output frame.
> 
> The idea is do decode both streams independently (threads) into the same
> overlay buffer, and have a third thread sample this at a regular rate
> (the wanted output frame rate), and feed that into the output chain
> (encoder + container). So, if at any given time one of the sources lags,
> the same frozen frame from it will be reused in several output frames
> (ie overlay buffer not updated in that area), but the overall output
> will not be stalled (as it is today).
> 
> Q1: is this doable with command-line flags to the ffmpeg executable ?

No.

> Q2: if not, I'd appreciate a sketch of where to look in the sources to
> do this in C.

Doing this is way more simple I think, it's just a matter of fetching a
new overlay frame at the right time depending on pts of the main video,
I don't think you need any threads here.

-- 
Baptiste COUDURIER
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