tutorial01.c

// tutorial01.c
//
// This tutorial was written by Stephen Dranger (dranger@gmail.com).
//
// Code based on a tutorial by Martin Bohme (boehme@inb.uni-luebeckREMOVETHIS.de)
// Tested on Gentoo, CVS version 5/01/07 compiled with GCC 4.1.1

// A small sample program that shows how to use libavformat and libavcodec to
// read video from a file.
//
// Use the Makefile to build all examples.
//
// Run using
//
// tutorial01 myvideofile.mpg
//
// to write the first five frames from "myvideofile.mpg" to disk in PPM
// format.

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>

#include <stdio.h>

void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
    FILE *pFile;
    char szFilename[32];
    int  y;

    // Open file
    sprintf(szFilename, "frame%d.ppm", iFrame);
    pFile = fopen(szFilename, "wb");

    if(pFile == NULL) {
        return;
    }

    // Write header
    fprintf(pFile, "P6\n%d %d\n255\n", width, height);

    // Write pixel data
    for(y = 0; y < height; y++) {
        fwrite(pFrame->data[0] + y * pFrame->linesize[0], 1, width * 3, pFile);
    }

    // Close file
    fclose(pFile);
}

int main(int argc, char *argv[]) {
    AVFormatContext *pFormatCtx = NULL;
    int             i, videoStream;
    AVCodecContext  *pCodecCtx = NULL;
    AVCodec         *pCodec = NULL;
    AVFrame         *pFrame = NULL;
    AVFrame         *pFrameRGB = NULL;
    AVPacket        packet;
    int             frameFinished;
    int             numBytes;
    uint8_t         *buffer = NULL;

    AVDictionary    *optionsDict = NULL;
    struct SwsContext      *sws_ctx = NULL;

    if(argc < 2) {
        printf("Please provide a movie file\n");
        return -1;
    }

    // Register all formats and codecs
    av_register_all();

    // Open video file
    if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0) {
        return -1;    // Couldn't open file
    }

    // Retrieve stream information
    if(avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        return -1;    // Couldn't find stream information
    }

    // Dump information about file onto standard error
    av_dump_format(pFormatCtx, 0, argv[1], 0);

    // Find the first video stream
    videoStream = -1;

    for(i = 0; i < pFormatCtx->nb_streams; i++)
        if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStream = i;
            break;
        }

    if(videoStream == -1) {
        return -1;    // Didn't find a video stream
    }

    // Get a pointer to the codec context for the video stream
    pCodecCtx = pFormatCtx->streams[videoStream]->codec;

    // Find the decoder for the video stream
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);

    if(pCodec == NULL) {
        fprintf(stderr, "Unsupported codec!\n");
        return -1; // Codec not found
    }

    // Open codec
    if(avcodec_open2(pCodecCtx, pCodec, &optionsDict) < 0) {
        return -1;    // Could not open codec
    }

    // Allocate video frame
    pFrame = av_frame_alloc();

    // Allocate an AVFrame structure
    pFrameRGB = av_frame_alloc();

    if(pFrameRGB == NULL) {
        return -1;
    }

    // Determine required buffer size and allocate buffer
    numBytes = avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
                                  pCodecCtx->height);
    buffer = (uint8_t *)av_malloc(numBytes * sizeof(uint8_t));

    sws_ctx =
        sws_getContext
        (
            pCodecCtx->width,
            pCodecCtx->height,
            pCodecCtx->pix_fmt,
            pCodecCtx->width,
            pCodecCtx->height,
            PIX_FMT_RGB24,
            SWS_BILINEAR,
            NULL,
            NULL,
            NULL
        );

    // Assign appropriate parts of buffer to image planes in pFrameRGB
    // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
    // of AVPicture
    avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
                   pCodecCtx->width, pCodecCtx->height);

    // Read frames and save first five frames to disk
    i = 0;

    while(av_read_frame(pFormatCtx, &packet) >= 0) {
        // Is this a packet from the video stream?
        if(packet.stream_index == videoStream) {
            // Decode video frame
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished,
                                  &packet);

            // Did we get a video frame?
            if(frameFinished) {
                // Convert the image from its native format to RGB
                sws_scale
                (
                    sws_ctx,
                    (uint8_t const * const *)pFrame->data,
                    pFrame->linesize,
                    0,
                    pCodecCtx->height,
                    pFrameRGB->data,
                    pFrameRGB->linesize
                );

                // Save the frame to disk
                if(++i <= 5)
                    SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height,
                              i);
            }
        }

        // Free the packet that was allocated by av_read_frame
        av_free_packet(&packet);
    }

    // Free the RGB image
    av_free(buffer);
    av_free(pFrameRGB);

    // Free the YUV frame
    av_free(pFrame);

    // Close the codec
    avcodec_close(pCodecCtx);

    // Close the video file
    avformat_close_input(&pFormatCtx);

    return 0;
}