Adding Customized Filters to FFmpeg: Unmentioned Dependences
If you're new to FFmpeg development and want to add customized filters, you might have followed the official filter tutorial and documentation. However, you may have noticed that the simplified example doesn't mention certain dependencies that are necessary for creating a custom filter.
Understanding FFmpeg Filters
FFmpeg filters are used to manipulate audio and video streams during transcoding, allowing you to perform various operations such as cropping, scaling, and color correction. Custom filters can be added to FFmpeg by creating a new filter that implements the desired functionality.
Dependences for Custom Filters
To create a custom filter for FFmpeg, you will need to have a working knowledge of the FFmpeg API and the filter framework. Additionally, you will need to have a basic understanding of the C programming language, as well as experience working with multithreaded applications.
FFmpeg Filter Framework
The FFmpeg filter framework is a powerful tool for creating custom filters. It provides a simple and flexible interface for defining filters, as well as a number of built-in functions for working with audio and video streams. To use the filter framework, you will need to familiarize yourself with the FFmpeg API and the various data structures and functions that are used to manipulate audio and video streams.
C Programming Language
Custom filters for FFmpeg are written in the C programming language. If you are not already familiar with C, you will need to learn the basics of the language before you can begin creating custom filters. There are many resources available online for learning C, including tutorials, books, and online courses.
Multithreaded Applications
FFmpeg is a multithreaded application, which means that it uses multiple threads to perform tasks concurrently. When creating custom filters, you will need to be aware of the threading model used by FFmpeg and how it affects the behavior of your filter. You will also need to ensure that your filter is thread-safe and does not cause any issues with the rest of the application.
Example of a Custom Filter
Here is an example of a simple custom filter that scales a video to a specified resolution:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "libavutil/avutil.h"
#include "libavutil/opt.h"
#include "libavfilter/avfilter.h"
typedef struct {
int width;
int height;
} ScaleContext;
static av_cold int init(AVFilterContext *ctx, const char *args)
{
ScaleContext *scale = ctx->priv;
int ret;
if ((ret = av\_parse\_int\_opt(NULL, "w", &scale->width, args,
AV\_OPT\_FLAG\_VIDEO\_PARAM|AV\_OPT\_FLAG\_FILTERING\_PARAM, 0)) < 0)
return ret;
if ((ret = av\_parse\_int\_opt(NULL, "h", &scale->height, args,
AV\_OPT\_FLAG\_VIDEO\_PARAM|AV\_OPT\_FLAG\_FILTERING\_PARAM, 0)) < 0)
return ret;
return 0;
}
static av\_cold void uninit(AVFilterContext *ctx)
{
ScaleContext *scale = ctx->priv;
av\_freep(&scale->width);
av\_freep(&scale->height);
}
static int filter_frame(AVFilterLink *inlink, AVFrame *in)
{
AVFilterLink *outlink = inlink->dst;
ScaleContext *scale = inlink->dst->priv;
AVFrame *out;
if (!scale->width || !scale->height) {
av\_log(NULL, AV\_LOG\_ERROR, "Invalid width or height
");
return AVERROR\_INVALIDDATA;
}
out = ff\_get\_video\_buffer(outlink, outlink->w, outlink->h);
if (!out)
return AVERROR(ENOMEM);
av\_picture\_copy(out->data, in->data, outlink->format, outlink->w, outlink->h);
out->pts = in->pts;
out->pkt\_dts = in->pkt\_dts;
out->pos = in->pos;
if (ff\_filter\_frame(outlink, out) < 0)
return AVERROR\_UNKNOWN;
return ff\_filter\_frame(inlink, in);
}
AVFilter ff\_scale = {
.name = "scale",
.description = NULL\_IF\_CONFIG\_SMALL("Scale the input video to the specified resolution"),
.priv\_size = sizeof(ScaleContext),
.init = init,
.uninit = uninit,
.query\_formats = NULL,
.filters = NULL,
.priv\_class = NULL,
.flags = AV\_FILTER\_FLAG\_VIDEO\_OUTPUT,
};- Creating custom filters for FFmpeg requires a working knowledge of the FFmpeg API and filter framework, as well as experience with the C programming language and multithreaded applications.
- The FFmpeg filter framework provides a simple and flexible interface for defining filters, and includes a number of built-in functions for working with audio and video streams.
- Custom filters for FFmpeg are written in the C programming language, and must be thread-safe to avoid causing issues with the rest of the application.