doc/examples: add decoding/filtering example program

doc/examples/Makefile

@@ -3,7 +3,7 @@ FFMPEG_LIBS=libavdevice libavformat libavfilter libavcodec libswscale libavutil
 CFLAGS+=$(shell pkg-config  --cflags $(FFMPEG_LIBS))
 LDFLAGS+=$(shell pkg-config --libs $(FFMPEG_LIBS))
 
-EXAMPLES=encoding metadata muxing
+EXAMPLES=encoding filtering metadata muxing
 
 OBJS=$(addsuffix .o,$(EXAMPLES))
 

doc/examples/filtering.c

+/*
+ * Copyright (c) 2010 Nicolas George
+ * Copyright (c) 2011 Stefano Sabatini
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/**
+ * @file
+ * API example for decoding and filtering
+ */
+
+#define _XOPEN_SOURCE 600 /* for usleep */
+
+#include <libavcodec/avcodec.h>
+#include <libavformat/avformat.h>
+#include <libavfilter/avfiltergraph.h>
+#include <libavfilter/vsink_buffer.h>
+#include <libavfilter/vsrc_buffer.h>
+
+const char *filter_descr = "scale=78:24";
+
+static AVFormatContext *fmt_ctx;
+static AVCodecContext *dec_ctx;
+AVFilterContext *buffersink_ctx;
+AVFilterContext *buffersrc_ctx;
+AVFilterGraph *filter_graph;
+static int video_stream_index = -1;
+static int64_t last_pts = AV_NOPTS_VALUE;
+
+static int open_input_file(const char *filename)
+{
+    int ret, i;
+    AVCodec *dec;
+
+    if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) < 0) {
+        av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
+        return ret;
+    }
+
+    if ((ret = av_find_stream_info(fmt_ctx)) < 0) {
+        av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
+        return ret;
+    }
+
+    /* select the video stream */
+    ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &dec, 0);
+    if (ret < 0) {
+        av_log(NULL, AV_LOG_ERROR, "Cannot find a video stream in the input file\n");
+        return ret;
+    }
+    video_stream_index = ret;
+    dec_ctx = fmt_ctx->streams[video_stream_index]->codec;
+
+    /* init the video decoder */
+    if ((ret = avcodec_open(dec_ctx, dec)) < 0) {
+        av_log(NULL, AV_LOG_ERROR, "Cannot open video decoder\n");
+        return ret;
+    }
+
+    return 0;
+}
+
+static int init_filters(const char *filters_descr)
+{
+    char args[512];
+    int ret;
+    AVFilter *buffersrc  = avfilter_get_by_name("buffer");
+    AVFilter *buffersink = avfilter_get_by_name("buffersink");
+    AVFilterInOut *outputs = avfilter_inout_alloc();
+    AVFilterInOut *inputs  = avfilter_inout_alloc();
+    enum PixelFormat pix_fmts[] = { PIX_FMT_GRAY8, PIX_FMT_NONE };
+    filter_graph = avfilter_graph_alloc();
+
+    /* buffer video source: the decoded frames from the decoder will be inserted here. */
+    snprintf(args, sizeof(args), "%d:%d:%d:%d:%d:%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);
+    ret = avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in",
+                                       args, NULL, filter_graph);
+    if (ret < 0) {
+        av_log(NULL, AV_LOG_ERROR, "Cannot create buffer source\n");
+        return ret;
+    }
+
+    /* buffer video sink: to terminate the filter chain. */
+    ret = avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out",
+                                       NULL, pix_fmts, filter_graph);
+    if (ret < 0) {
+        av_log(NULL, AV_LOG_ERROR, "Cannot create buffer sink\n");
+        return ret;
+    }
+
+    /* Endpoints for the filter graph. */
+    outputs->name       = av_strdup("in");
+    outputs->filter_ctx = buffersrc_ctx;
+    outputs->pad_idx    = 0;
+    outputs->next       = NULL;
+
+    inputs->name       = av_strdup("out");
+    inputs->filter_ctx = buffersink_ctx;
+    inputs->pad_idx    = 0;
+    inputs->next       = NULL;
+
+    if ((ret = avfilter_graph_parse(filter_graph, filter_descr,
+                                    &inputs, &outputs, NULL)) < 0)
+        return ret;
+
+    if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
+        return ret;
+}
+
+static void display_picref(AVFilterBufferRef *picref, AVRational time_base)
+{
+    int x, y;
+    uint8_t *p0, *p;
+    int64_t delay;
+
+    if (picref->pts != AV_NOPTS_VALUE) {
+        if (last_pts != AV_NOPTS_VALUE) {
+            /* sleep roughly the right amount of time;
+             * usleep is in microseconds, just like AV_TIME_BASE. */
+            delay = av_rescale_q(picref->pts - last_pts,
+                                 time_base, AV_TIME_BASE_Q);
+            if (delay > 0 && delay < 1000000)
+                usleep(delay);
+        }
+        last_pts = picref->pts;
+    }
+
+    /* Trivial ASCII grayscale display. */
+    p0 = picref->data[0];
+    puts("\033c");
+    for (y = 0; y < picref->video->h; y++) {
+        p = p0;
+        for (x = 0; x < picref->video->w; x++)
+            putchar(" .-+#"[*(p++) / 52]);
+        putchar('\n');
+        p0 += picref->linesize[0];
+    }
+    fflush(stdout);
+}
+
+int main(int argc, char **argv)
+{
+    int ret;
+    AVPacket packet;
+    AVFrame frame;
+    int got_frame;
+
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s file\n", argv[0]);
+        exit(1);
+    }
+
+    avcodec_register_all();
+    av_register_all();
+    avfilter_register_all();
+
+    if ((ret = open_input_file(argv[1]) < 0))
+        goto end;
+    if ((ret = init_filters(filter_descr)) < 0)
+        goto end;
+
+    /* read all packets */
+    while (1) {
+        AVFilterBufferRef *picref;
+        if ((ret = av_read_frame(fmt_ctx, &packet)) < 0)
+            break;
+
+        if (packet.stream_index == video_stream_index) {
+            avcodec_get_frame_defaults(&frame);
+            got_frame = 0;
+            ret = avcodec_decode_video2(dec_ctx, &frame, &got_frame, &packet);
+            av_free_packet(&packet);
+            if (ret < 0) {
+                av_log(NULL, AV_LOG_ERROR, "Error decoding video\n");
+                break;
+            }
+
+            if (got_frame) {
+                if (frame.pts == AV_NOPTS_VALUE)
+                    frame.pts = frame.pkt_dts == AV_NOPTS_VALUE ?
+                        frame.pkt_dts : frame.pkt_pts;
+                /* push the decoded frame into the filtergraph */
+                av_vsrc_buffer_add_frame(buffersrc_ctx, &frame);
+
+                /* pull filtered pictures from the filtergraph */
+                while (avfilter_poll_frame(buffersink_ctx->inputs[0])) {
+                    av_vsink_buffer_get_video_buffer_ref(buffersink_ctx, &picref, 0);
+                    if (picref) {
+                        display_picref(picref, buffersink_ctx->inputs[0]->time_base);
+                        avfilter_unref_buffer(picref);
+                    }
+                }
+            }
+        }
+    }
+end:
+    avfilter_graph_free(&filter_graph);
+    if (dec_ctx)
+        avcodec_close(dec_ctx);
+    av_close_input_file(fmt_ctx);
+
+    if (ret < 0 && ret != AVERROR_EOF) {
+        char buf[1024];
+        av_strerror(ret, buf, sizeof(buf));
+        fprintf(stderr, "Error occurred: %s\n", buf);
+        exit(1);
+    }
+
+    exit(0);
+}