Add decode_frame example: How to decode one video frame at timestamp

..and convet to RGB if desired.

3 files changed, 187 insertions, 0 deletions

diff --git a/src/.gitignore b/src/.gitignore
new file mode 100644
index 0000000..75500be
--- /dev/null
+++ b/src/.gitignore
@@ -0,0 +1 @@
+decode_frame
diff --git a/src/Makefile b/src/Makefile
index f61114a..29ffd29 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,5 +1,11 @@
 CFLAGS=-std=c99 -Wall
 LibAV=`pkg-config --cflags --libs libavcodec`
+LIBAV_DECODE_FLAGS=$(shell pkg-config --libs --cflags libavformat libavcodec libavutil libswscale)
+
+all: advtime decode_frame
 
 advtime: advtime.c
 	gcc ${LibAV} advtime.c -o $@
+
+decode_frame: decode_frame.c
+	gcc $(CFLAGS) $(LIBAV_DECODE_FLAGS) decode_frame.c -o $@
diff --git a/src/decode_frame.c b/src/decode_frame.c
new file mode 100644
index 0000000..717e81c
--- /dev/null
+++ b/src/decode_frame.c
@@ -0,0 +1,180 @@
+#define DEBUG 0
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#include <libavformat/avformat.h>
+#include <libavcodec/avcodec.h>
+#include <libavutil/avutil.h>
+#include <libswscale/swscale.h>
+
+static void
+pgm_save(unsigned char *buf, int wrap, int xsize, int ysize, char *filename)
+{
+    FILE *f;
+    int i;
+
+    f = fopen(filename, "w");
+    fprintf(f, "P5\n%d %d\n%d\n", xsize, ysize, 255);
+    for(i=0; i < ysize; i++)
+        fwrite(buf + i * wrap, 1, xsize, f);
+    fclose(f);
+}
+
+static void
+ppm_save(unsigned char *buf, int wrap, int xsize, int ysize, char *filename)
+{
+    FILE *f;
+    int i;
+
+    f = fopen(filename, "w");
+    fprintf(f,"P6\n%d %d\n%d\n", xsize, ysize, 255);
+    for(i=0; i < ysize; i++)
+        fwrite(buf + i * wrap, 3, xsize, f);
+    fclose(f);
+}
+
+int
+main(int argc, char *argv[])
+{
+	const char *filename = argv[1];
+	AVFormatContext *fmt_ctx = NULL;
+	int vid_stream = -1;
+	AVCodecContext *codec_ctx = NULL;
+	AVCodec *codec;
+	AVFrame *frame;
+	AVPacket packet;
+	int bytes_decoded, got_picture;
+	AVFrame *frame_rgb;
+	int nbytes;
+	uint8_t *buffer;
+	struct SwsContext *sws_ctx;
+	int timestamp = 0;
+
+	av_register_all();
+#if DEBUG
+	av_log_set_level(AV_LOG_DEBUG);
+	printf("file: %s\n", filename);
+#endif
+	
+	if (argc < 2) {
+		fprintf(stderr, "usage: %s filename [timestamp]\n", argv[0]);
+		exit(1);
+	}
+	if (avformat_open_input(&fmt_ctx, filename, NULL, NULL) != 0)
+		exit(2);
+
+	if (avformat_find_stream_info(fmt_ctx, NULL) < 0)
+		exit(3);
+
+#if DEBUG
+	av_dump_format(fmt_ctx, 0, filename, 0);
+#endif
+
+	vid_stream = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_VIDEO,
+					 -1, -1, NULL, 0);
+	if (vid_stream == -1)
+		exit(4);
+	codec_ctx = fmt_ctx->streams[vid_stream]->codec;
+
+	timestamp = fmt_ctx->start_time==AV_NOPTS_VALUE ? 0:fmt_ctx->start_time;
+#if 1
+	if (argc == 3 && atoi(argv[2]) > 0)
+		timestamp += atoi(argv[2]);
+#endif
+	avformat_seek_file(fmt_ctx, -1, INT64_MIN, timestamp, INT64_MAX, 0);
+
+	codec = avcodec_find_decoder(codec_ctx->codec_id);
+	if (codec == NULL) {
+		fprintf(stderr, "Failed to find decoder!\n");
+		exit(5);
+	}
+
+#if DEBUG
+	printf("has cap truncated: %d\n",
+	       codec->capabilities & CODEC_CAP_TRUNCATED);
+#endif
+#if 0
+	if (codec->capabilities & CODEC_CAP_TRUNCATED)
+		codec_ctx->flags |= CODEC_FLAG_TRUNCATED;
+#endif
+
+	if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
+		fprintf(stderr, "Failed to open codec!\n");
+		exit(6);
+	}
+
+	packet.data = NULL;
+	do {
+		if (packet.data != NULL)
+			av_free_packet(&packet);
+		if (av_read_frame(fmt_ctx, &packet) < 0) {
+			fprintf(stderr, "Found no video stream packet!\n");
+			exit(30);
+		}
+	} while (packet.stream_index != vid_stream);
+
+	frame = avcodec_alloc_frame();
+	do {
+#if DEBUG
+		printf("packet.data: %p, packet.size: %d, packet.stream_index: %d\n",
+		       packet.data, packet.size, packet.stream_index);
+#endif
+
+		bytes_decoded = avcodec_decode_video2(codec_ctx, frame,
+						      &got_picture, &packet);
+		if (bytes_decoded < 0) {
+			fprintf(stderr, "Error while decoding frame!\n");
+			exit(12);
+		}
+#if DEBUG
+		printf("bytes_decoded: %d, got_picture: %d\n",
+		       bytes_decoded, got_picture);
+#endif
+		
+	} while (got_picture == 0 && packet.size > 0);
+	av_free_packet(&packet);
+	if (got_picture == 0)
+		exit(9);
+
+	pgm_save(frame->data[0], frame->linesize[0],
+		 codec_ctx->width, codec_ctx->height, "foo.pgm");
+
+#define CONVERT_TO_RGB 1
+#if CONVERT_TO_RGB
+	frame_rgb = avcodec_alloc_frame();
+	if (!frame_rgb)
+		exit(9);
+
+	nbytes = avpicture_get_size(PIX_FMT_RGB24,
+					codec_ctx->width, codec_ctx->height);
+	buffer = calloc(nbytes, sizeof(uint8_t));
+	if (!buffer)
+		exit(10);
+	avpicture_fill((AVPicture *) frame_rgb, buffer, PIX_FMT_RGB24,
+		       codec_ctx->width, codec_ctx->height);
+
+	sws_ctx = sws_getCachedContext(NULL,
+				       codec_ctx->width, codec_ctx->height,
+				       codec_ctx->pix_fmt,
+				       codec_ctx->width, codec_ctx->height,
+				       PIX_FMT_RGB24, SWS_BILINEAR,
+				       NULL, NULL, NULL);
+
+	sws_scale(sws_ctx,
+		  (const uint8_t *const *) frame->data, frame->linesize, 0,
+		  codec_ctx->height,  frame_rgb->data, frame_rgb->linesize);
+
+	ppm_save(frame_rgb->data[0], frame_rgb->linesize[0],
+		 codec_ctx->width, codec_ctx->height, "foo.ppm");
+#endif
+
+	free(buffer);
+	av_free(frame_rgb);
+	av_free(frame);
+	avcodec_close(codec_ctx);
+	avformat_close_input(&fmt_ctx);
+
+	return 0;
+}