dump_format(ic, nb_input_files, v4l_device, 0);
dump_format(ic, nb_input_files, video_device, 0);
void prepare_grab(void){    int has_video, has_audio, i, j;    AVFormatContext *oc;    AVFormatContext *ic;    AVFormatParameters ap1, *ap = &ap1;    /* see if audio/video inputs are needed */    has_video = 0;    has_audio = 0;    memset(ap, 0, sizeof(*ap));    for(j=0;j<nb_output_files;j++) {        oc = output_files[j];        for(i=0;i<oc->nb_streams;i++) {            AVCodecContext *enc = &oc->streams[i]->codec;            switch(enc->codec_type) {            case CODEC_TYPE_AUDIO:                if (enc->sample_rate > ap->sample_rate)                    ap->sample_rate = enc->sample_rate;                if (enc->channels > ap->channels)                    ap->channels = enc->channels;                has_audio = 1;                break;            case CODEC_TYPE_VIDEO:                if (enc->width > ap->width)                    ap->width = enc->width;                if (enc->height > ap->height)                    ap->height = enc->height;                if (enc->frame_rate > ap->frame_rate)                    ap->frame_rate = enc->frame_rate;                has_video = 1;                break;            default:                av_abort();            }        }    }        if (has_video == 0 && has_audio == 0) {        fprintf(stderr, "Output file must have at least one audio or video stream\n");        exit(1);    }        if (has_video) {        AVInputFormat *fmt1;        fmt1 = av_find_input_format("video_grab_device");        if (av_open_input_file(&ic, "", fmt1, 0, ap) < 0) {            fprintf(stderr, "Could not find video grab device\n");            exit(1);        }        /* by now video grab has one stream */        ic->streams[0]->r_frame_rate = ap->frame_rate;        input_files[nb_input_files] = ic;        dump_format(ic, nb_input_files, v4l_device, 0);        nb_input_files++;    }    if (has_audio) {        AVInputFormat *fmt1;        fmt1 = av_find_input_format("audio_device");        if (av_open_input_file(&ic, "", fmt1, 0, ap) < 0) {            fprintf(stderr, "Could not find audio grab device\n");            exit(1);        }        input_files[nb_input_files] = ic;        dump_format(ic, nb_input_files, audio_device, 0);        nb_input_files++;    }}