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* copyright (c) 2013 Andrew Kelley
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* This file is part of FFmpeg.
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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* libavfilter API usage example.
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* @example filter_audio.c
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* This example will generate a sine wave audio,
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* pass it through a simple filter chain, and then compute the MD5 checksum of
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* The filter chain it uses is:
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* (input) -> abuffer -> volume -> aformat -> abuffersink -> (output)
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* abuffer: This provides the endpoint where you can feed the decoded samples.
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* volume: In this example we hardcode it to 0.90.
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* aformat: This converts the samples to the samplefreq, channel layout,
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* and sample format required by the audio device.
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* abuffersink: This provides the endpoint where you can read the samples after
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* they have passed through the filter chain.
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#include "libavutil/channel_layout.h"
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#include "libavutil/md5.h"
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#include "libavutil/mem.h"
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#include "libavutil/opt.h"
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#include "libavutil/samplefmt.h"
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#include "libavfilter/avfilter.h"
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#include "libavfilter/buffersink.h"
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#include "libavfilter/buffersrc.h"
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#define INPUT_SAMPLERATE 48000
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#define INPUT_FORMAT AV_SAMPLE_FMT_FLTP
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#define INPUT_CHANNEL_LAYOUT AV_CH_LAYOUT_5POINT0
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#define VOLUME_VAL 0.90
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static int init_filter_graph(AVFilterGraph **graph, AVFilterContext **src,
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AVFilterContext **sink)
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AVFilterGraph *filter_graph;
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AVFilterContext *abuffer_ctx;
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AVFilterContext *volume_ctx;
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AVFilterContext *aformat_ctx;
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AVFilterContext *abuffersink_ctx;
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AVFilter *abuffersink;
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AVDictionary *options_dict = NULL;
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uint8_t options_str[1024];
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uint8_t ch_layout[64];
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/* Create a new filtergraph, which will contain all the filters. */
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filter_graph = avfilter_graph_alloc();
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fprintf(stderr, "Unable to create filter graph.\n");
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return AVERROR(ENOMEM);
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/* Create the abuffer filter;
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* it will be used for feeding the data into the graph. */
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abuffer = avfilter_get_by_name("abuffer");
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fprintf(stderr, "Could not find the abuffer filter.\n");
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return AVERROR_FILTER_NOT_FOUND;
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abuffer_ctx = avfilter_graph_alloc_filter(filter_graph, abuffer, "src");
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fprintf(stderr, "Could not allocate the abuffer instance.\n");
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return AVERROR(ENOMEM);
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/* Set the filter options through the AVOptions API. */
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av_get_channel_layout_string(ch_layout, sizeof(ch_layout), 0, INPUT_CHANNEL_LAYOUT);
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av_opt_set (abuffer_ctx, "channel_layout", ch_layout, AV_OPT_SEARCH_CHILDREN);
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av_opt_set (abuffer_ctx, "sample_fmt", av_get_sample_fmt_name(INPUT_FORMAT), AV_OPT_SEARCH_CHILDREN);
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av_opt_set_q (abuffer_ctx, "time_base", (AVRational){ 1, INPUT_SAMPLERATE }, AV_OPT_SEARCH_CHILDREN);
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av_opt_set_int(abuffer_ctx, "sample_rate", INPUT_SAMPLERATE, AV_OPT_SEARCH_CHILDREN);
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/* Now initialize the filter; we pass NULL options, since we have already
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* set all the options above. */
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err = avfilter_init_str(abuffer_ctx, NULL);
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fprintf(stderr, "Could not initialize the abuffer filter.\n");
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/* Create volume filter. */
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volume = avfilter_get_by_name("volume");
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fprintf(stderr, "Could not find the volume filter.\n");
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return AVERROR_FILTER_NOT_FOUND;
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volume_ctx = avfilter_graph_alloc_filter(filter_graph, volume, "volume");
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fprintf(stderr, "Could not allocate the volume instance.\n");
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return AVERROR(ENOMEM);
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/* A different way of passing the options is as key/value pairs in a
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av_dict_set(&options_dict, "volume", AV_STRINGIFY(VOLUME_VAL), 0);
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err = avfilter_init_dict(volume_ctx, &options_dict);
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av_dict_free(&options_dict);
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fprintf(stderr, "Could not initialize the volume filter.\n");
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/* Create the aformat filter;
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* it ensures that the output is of the format we want. */
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aformat = avfilter_get_by_name("aformat");
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fprintf(stderr, "Could not find the aformat filter.\n");
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return AVERROR_FILTER_NOT_FOUND;
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aformat_ctx = avfilter_graph_alloc_filter(filter_graph, aformat, "aformat");
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fprintf(stderr, "Could not allocate the aformat instance.\n");
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return AVERROR(ENOMEM);
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/* A third way of passing the options is in a string of the form
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* key1=value1:key2=value2.... */
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snprintf(options_str, sizeof(options_str),
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"sample_fmts=%s:sample_rates=%d:channel_layouts=0x%"PRIx64,
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av_get_sample_fmt_name(AV_SAMPLE_FMT_S16), 44100,
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(uint64_t)AV_CH_LAYOUT_STEREO);
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err = avfilter_init_str(aformat_ctx, options_str);
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av_log(NULL, AV_LOG_ERROR, "Could not initialize the aformat filter.\n");
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/* Finally create the abuffersink filter;
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* it will be used to get the filtered data out of the graph. */
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abuffersink = avfilter_get_by_name("abuffersink");
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fprintf(stderr, "Could not find the abuffersink filter.\n");
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return AVERROR_FILTER_NOT_FOUND;
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abuffersink_ctx = avfilter_graph_alloc_filter(filter_graph, abuffersink, "sink");
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if (!abuffersink_ctx) {
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fprintf(stderr, "Could not allocate the abuffersink instance.\n");
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return AVERROR(ENOMEM);
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/* This filter takes no options. */
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err = avfilter_init_str(abuffersink_ctx, NULL);
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fprintf(stderr, "Could not initialize the abuffersink instance.\n");
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/* Connect the filters;
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* in this simple case the filters just form a linear chain. */
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err = avfilter_link(abuffer_ctx, 0, volume_ctx, 0);
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err = avfilter_link(volume_ctx, 0, aformat_ctx, 0);
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err = avfilter_link(aformat_ctx, 0, abuffersink_ctx, 0);
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fprintf(stderr, "Error connecting filters\n");
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/* Configure the graph. */
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err = avfilter_graph_config(filter_graph, NULL);
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av_log(NULL, AV_LOG_ERROR, "Error configuring the filter graph\n");
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*graph = filter_graph;
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*sink = abuffersink_ctx;
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/* Do something useful with the filtered data: this simple
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* example just prints the MD5 checksum of each plane to stdout. */
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static int process_output(struct AVMD5 *md5, AVFrame *frame)
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int planar = av_sample_fmt_is_planar(frame->format);
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int channels = av_get_channel_layout_nb_channels(frame->channel_layout);
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int planes = planar ? channels : 1;
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int bps = av_get_bytes_per_sample(frame->format);
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int plane_size = bps * frame->nb_samples * (planar ? 1 : channels);
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for (i = 0; i < planes; i++) {
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uint8_t checksum[16];
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av_md5_sum(checksum, frame->extended_data[i], plane_size);
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fprintf(stdout, "plane %d: 0x", i);
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for (j = 0; j < sizeof(checksum); j++)
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fprintf(stdout, "%02X", checksum[j]);
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fprintf(stdout, "\n");
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fprintf(stdout, "\n");
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/* Construct a frame of audio data to be filtered;
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* this simple example just synthesizes a sine wave. */
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static int get_input(AVFrame *frame, int frame_num)
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#define FRAME_SIZE 1024
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/* Set up the frame properties and allocate the buffer for the data. */
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frame->sample_rate = INPUT_SAMPLERATE;
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frame->format = INPUT_FORMAT;
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frame->channel_layout = INPUT_CHANNEL_LAYOUT;
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frame->nb_samples = FRAME_SIZE;
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frame->pts = frame_num * FRAME_SIZE;
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err = av_frame_get_buffer(frame, 0);
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/* Fill the data for each channel. */
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for (i = 0; i < 5; i++) {
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float *data = (float*)frame->extended_data[i];
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for (j = 0; j < frame->nb_samples; j++)
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data[j] = sin(2 * M_PI * (frame_num + j) * (i + 1) / FRAME_SIZE);
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int main(int argc, char *argv[])
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AVFilterGraph *graph;
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AVFilterContext *src, *sink;
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uint8_t errstr[1024];
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int err, nb_frames, i;
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fprintf(stderr, "Usage: %s <duration>\n", argv[0]);
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duration = atof(argv[1]);
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nb_frames = duration * INPUT_SAMPLERATE / FRAME_SIZE;
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if (nb_frames <= 0) {
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fprintf(stderr, "Invalid duration: %s\n", argv[1]);
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avfilter_register_all();
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/* Allocate the frame we will be using to store the data. */
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frame = av_frame_alloc();
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fprintf(stderr, "Error allocating the frame\n");
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md5 = av_md5_alloc();
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fprintf(stderr, "Error allocating the MD5 context\n");
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/* Set up the filtergraph. */
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err = init_filter_graph(&graph, &src, &sink);
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fprintf(stderr, "Unable to init filter graph:");
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/* the main filtering loop */
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for (i = 0; i < nb_frames; i++) {
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/* get an input frame to be filtered */
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err = get_input(frame, i);
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fprintf(stderr, "Error generating input frame:");
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/* Send the frame to the input of the filtergraph. */
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err = av_buffersrc_add_frame(src, frame);
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av_frame_unref(frame);
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fprintf(stderr, "Error submitting the frame to the filtergraph:");
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/* Get all the filtered output that is available. */
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while ((err = av_buffersink_get_frame(sink, frame)) >= 0) {
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/* now do something with our filtered frame */
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err = process_output(md5, frame);
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fprintf(stderr, "Error processing the filtered frame:");
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av_frame_unref(frame);
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if (err == AVERROR(EAGAIN)) {
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/* Need to feed more frames in. */
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} else if (err == AVERROR_EOF) {
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/* Nothing more to do, finish. */
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} else if (err < 0) {
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/* An error occurred. */
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fprintf(stderr, "Error filtering the data:");
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avfilter_graph_free(&graph);
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av_frame_free(&frame);
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av_strerror(err, errstr, sizeof(errstr));
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fprintf(stderr, "%s\n", errstr);