Ffmeg filter Introduction [GO]

in FFmpeg, the reverse interleaving needs to use the avfilter, that is, the image filter, FFmpeg has a lot of filters, very powerful, anti-interleaving filter is yadif.

The basic filter usage flow is:

decoded Screen--->buffer filter----> Other filters---->buffersink Filter---> Finished screen

All filters form the filter chain, the two filters that must be the buffer filter and the Buffersink filter, the former function is to load the decoded screen into the filter chain, The role of the latter is to read the processed picture from the filter chain. Then the anti-interlacing filter chain should look like this: Buffer filter--->yadif Filter--->buffersink filter

Filter-related structures:

avfiltergraph: Managing all filter Images

Avfiltercontext: Filter Context

Avfilter: Filter

Here's how to create a filter chain:

The first step is to create the Avfiltergraph

avfiltergraph *filter_graph=avfilter_graph_alloc ();

The second step is to get the filter you want to use:

Avfilter *filter_buffer=avfilter_get_by_name ("buffer");

Avfilter *filter_yadif=avfilter_get_by_name ("Yadif");

Avfilter *filter_buffersink=avfilter_get_by_name ("Buffersink");

The third step is to create the filter context, which is Avfiltercontext:

int Avfilter_graph_create_filter (Avfiltercontext **filt_ctx, const avfilter *filt,
const char *name, const char *args, void *opaque,
Avfiltergraph *graph_ctx);

Parameter description: Filt_ctx is used to save the created filter context, filt is the filter, name is the filter name (should be unique in the filter chain), args is passed to the filter parameters (each filter is different, can be found in the corresponding filter code), Opaque is not used in the code, GRAPH_CTX is a filter image management pointer. Example:

Avfiltercontext *filter_buffer_ctx,*filter_yadif_ctx,*filter_buffersink_ctx;

Create buffer Filter

snprintf (args, sizeof (args),
"Video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
Dec_ctx->width, Dec_ctx->height, DEC_CTX->PIX_FMT,
Dec_ctx->time_base.num, Dec_ctx->time_base.den,
Dec_ctx->sample_aspect_ratio.num, Dec_ctx->sample_aspect_ratio.den);
Avfilter_graph_create_filter (&filter_buffer_ctx, Avfilter_get_by_name ("buffer"), "in",
Args, NULL, filter_graph);

Create a YADIF filter

Avfilter_graph_create_filter (&Filter_yadif_ctx, Avfilter_get_by_name ("Yadif"), "Yadif",
"Mode=send_frame:parity=auto:deint=interlaced", NULL, Filter_graph);

Create a Buffersink filter

Enum Avpixelformat pix_fmts[] = {av_pix_fmt_yuv420p, av_pix_fmt_none};

Avfilter_graph_create_filter (&filter_buffersink_ctx, Avfilter_get_by_name ("Buffersink"), "out",
NULL, null,filter_graph);

Av_opt_set_int_list (Filter_buffersink_ctx, "Pix_fmts", Pix_fmts,
Av_pix_fmt_none, Av_opt_search_children);

Fourth step, connect the filter

Avfilter_link (filter_buffer_ctx, 0, filter_yadif_ctx, 0);

Avfilter_link (filter_yadif_ctx, 0, filter_buffersink_ctx, 0);

Fifth step, check that all configurations are correct:

if (ret = Avfilter_graph_config (player->filter_graph, NULL)) < 0) {
LOGE (0, "avfilter_graph_config:%d\n", ret);
Goto end;
}

Note that all of the above functions should check the return value, which is a bit of a write-down, and the filter chain is created if there is no error.

How to filter using a filter chain, mainly using two functions:

Pushes the decoded frame to the filter chain

int Av_buffersrc_add_frame_flags (Avfiltercontext *buffer_src,
Avframe *frame, int flags);

Pull out the processed frame:

int Av_buffersink_get_frame (Avfiltercontext *ctx, Avframe *frame);
For example:

Av_buffersrc_add_frame_flags (Filter_buffer_ctx, Orgin_frame, av_buffersrc_flag_keep_ref);

while (1) {

ret = Av_buffersink_get_frame (filter_buffersink_ctx, frame);
if (ret = = Averror (eagain) | | ret = = averror_eof) {
Break
}

Display (frame);

};

Image contrast before and after anti-interlacing:

Although it is rather vague, the transverse lines are indeed removed.

Find a bit, found that there is an anti-interleaving filter kerndeint, is the GPL ffmpeg, use to configure open GPL

After passing in parameter thresh=0:map=0:order=1:sharp=0:twoway=0, it seems better than yadif, the effect is as follows:

FFmpeg also has some deinterlace filters, the test found in the filter time and screen quality, the better is the pp/lb filter.

Ffmeg filter Introduction [GO]