[Libav-user] Overlay filter (add Watermark to video)

[Alberto Martín Fernandez]

Hi;

I am using ffmpeg 1.0.9 & SDL 1.2 and i am trying to add a watermark.
I started to implement my media player basing on the ffplay example, adding
funtionalities, buttons...

I have to implement an overlay filter, so i do:

FILTER 1:(Video base) INPUT
   avfilter_graph_create_filter(&filt_src, avfilter_get_by_name("buffer"),
"in", buffersrc_args,NULL,graph);

FILTER 2: (overlay filter, watermark(png)) INPUT

avfilter_graph_create_filter(&bufferovrlay_ctx,avfilter_get_by_name("overlay"),
"overlay",  argsStrOvrlay, NULL, graph);

FILTER 3: (buffersink filter) OUTPUT
    avfilter_graph_create_filter(&filt_out,
avfilter_get_by_name("ffbuffersink"),
"out", NULL, buffersink_params, graph);

Then i call :
avfilter_graph_parse(graph,
"buffer=video_size=640x360:pix_fmt=0:time_base=1001/3000:pixel_aspect=0/1
[in_1]; buffer=video_size=512x128:pix_fmt=2:time_base=1/1:pixel_aspect=0
[in_2]; [in_1] [in_2] overlay=0:0 [out]; [out] buffersink", inputs,
&outputs, NULL);

Then i call avfilter_graph_config(graph, NULL);
and it returnrs -22 error (AVERROR_INVALIDDATA)

I have some questions:

Which are the correct parameters to set in a overlay filter (argsStrOvrlay)?
I set sprintf_s(argsStrOvrlay, sizeof(argsStrOvrlay),
"video_size=%dx%d:pix_fmt=%d:time_base=1/1:pixel_aspect=0",
pCodecCtxImage->width, pCodecCtxImage->height, pCodecCtxImage->pix_fmt);

I am not sure if i need to link the filters using avfilter_link.

Has anyone an example of adding a watermark image to a video using overlay
filter?
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