/* set end of buffer to 0 (this ensures that no overreading happens for damaged mpeg streams) */ memset(inbuf + INBUF_SIZE, 0, FF_INPUT_BUFFER_PADDING_SIZE);
printf("Video decoding\n");
/* find the mpeg1 video decoder */ //codec = avcodec_find_decoder(CODEC_ID_H264); codec = avcodec_find_decoder(CODEC_ID_MPEG2VIDEO); if (!codec) { fprintf(stderr, "codec not found\n"); exit(1); }
if(codec->capabilities&CODEC_CAP_TRUNCATED) c->flags|= CODEC_FLAG_TRUNCATED; /* we dont send complete frames */
/* for some codecs, such as msmpeg4 and mpeg4, width and height MUST be initialized there because these info are not available in the bitstream */
/* open it */ if (avcodec_open(c, codec) < 0) { fprintf(stderr, "could not open codec\n"); exit(1); }
/* the codec gives us the frame size, in samples */ f = fopen(filename, "rb"); if (!f) { fprintf(stderr, "could not open %s\n", filename); exit(1); } frame = 0; for(;;) { AVPacket pkt;
/* NOTE1: some codecs are stream based (mpegvideo, mpegaudio) and this is the only method to use them because you cannot know the compressed data size before analysing it.
BUT some other codecs (msmpeg4, mpeg4) are inherently frame based, so you must call them with all the data for one frame exactly. You must also initialize ‘width‘ and ‘height‘ before initializing them. */
/* NOTE2: some codecs allow the raw parameters (frame size, sample rate) to be changed at any frame. We handle this, so you should also take care of it */
/* here, we use a stream based decoder (mpeg1video), so we feed decoder and see if it could decode a frame */ pkt_len = pkt.size; pkt_ptr = pkt.data;
// inbuf_ptr = inbuf; while (pkt_len > 0) { len = avcodec_decode_video2(c, picture, &got_picture, &pkt); if (len < 0) { fprintf(stderr, "Error while decoding frame %d\n", frame); exit(1); } if (got_picture) { printf("saving frame %3d\n", frame); fflush(stdout);
/* the picture is allocated by the decoder. no need to free it */ snprintf(buf, sizeof(buf), outfilename, frame); pgm_save(picture->data[0], picture->linesize[0], c->width, c->height, buf); frame++; } size -= len; inbuf_ptr += len; } av_free_packet(&pkt); }
/* some codecs, such as MPEG, transmit the I and P frame with a latency of one frame. You must do the following to have a chance to get the last frame of the video */ len = avcodec_decode_video2(c, picture, &got_picture, NULL); if (got_picture) { printf("saving last frame %3d\n", frame); fflush(stdout);
/* the picture is allocated by the decoder. no need to free it */ snprintf(buf, sizeof(buf), outfilename, frame); pgm_save(picture->data[0], picture->linesize[0], c->width, c->height, buf); frame++; }
