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| int main(int argc, char *argv[])
{
AVFormatContext *input_ctx = NULL;
int video_stream, ret;
AVStream *video = NULL;
AVCodecContext *decoder_ctx = NULL;
const AVCodec *decoder = NULL;
AVPacket *packet = NULL;
enum AVHWDeviceType type;
int i;
if (argc < 4) {
fprintf(stderr, "Usage: %s <device type> <input file> <output file>\n", argv[0]);
return -1;
}
//根据传入加速器名字，找到对应的type
type = av_hwdevice_find_type_by_name(argv[1]);
if (type == AV_HWDEVICE_TYPE_NONE) {
fprintf(stderr, "Device type %s is not supported.\n", argv[1]);
fprintf(stderr, "Available device types:");
//没找到加速器，打印ffmepg 支持的加速器列表
while((type = av_hwdevice_iterate_types(type)) != AV_HWDEVICE_TYPE_NONE)
fprintf(stderr, " %s", av_hwdevice_get_type_name(type));
fprintf(stderr, "\n");
return -1;
}
//申请packet保存解码前数据
packet = av_packet_alloc();
if (!packet) {
fprintf(stderr, "Failed to allocate AVPacket\n");
return -1;
}
//打开输入的文件，关联到AVFormatContext
if (avformat_open_input(&input_ctx, argv[2], NULL, NULL) != 0) {
fprintf(stderr, "Cannot open input file '%s'\n", argv[2]);
return -1;
}
//填充AVFormatContext，获取解封装信息
if (avformat_find_stream_info(input_ctx, NULL) < 0) {
fprintf(stderr, "Cannot find input stream information.\n");
return -1;
}
//找到video 对应的stream index， 获取对应的解码器信息
ret = av_find_best_stream(input_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &decoder, 0);
if (ret < 0) {
fprintf(stderr, "Cannot find a video stream in the input file\n");
return -1;
}
video_stream = ret;
//遍历获取解码器对应的硬件配置信息
for (i = 0;; i++) {
const AVCodecHWConfig *config = avcodec_get_hw_config(decoder, i);
//如果没找到支持的config，结束程序
if (!config) {
fprintf(stderr, "Decoder %s does not support device type %s.\n",
decoder->name, av_hwdevice_get_type_name(type));
return -1;
}
/*
如果config的device_type匹配我们设置的类型，并且config的methods的值为AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX
保存支持的hw_pix_fmt，跳出循环
关于AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX
如果我们选择了此种类型，需要在调用avcodec_open2()打开解码器之前，给AVCodecContext.hw_device_ctx设置正确的值。
*/
if (config->methods & AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX &&
config->device_type == type) {
hw_pix_fmt = config->pix_fmt;
break;
}
}
//创建解码器上下文
if (!(decoder_ctx = avcodec_alloc_context3(decoder)))
return AVERROR(ENOMEM);
video = input_ctx->streams[video_stream];
//给解码器上下文填充参数，复制从文件中读的的解码器参数
if (avcodec_parameters_to_context(decoder_ctx, video->codecpar) < 0)
return -1;
//get_format是一个函数指针，我们给ffmpeg提供一个函数，ffmpeg 调用该函数确定解码帧的数据格式
decoder_ctx->get_format = get_hw_format;
//根据AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE_CTX的定义，我们需要给ctx->hw_device_ctx赋值
if (hw_decoder_init(decoder_ctx, type) < 0)
return -1;
//打开解码器
if ((ret = avcodec_open2(decoder_ctx, decoder, NULL)) < 0) {
fprintf(stderr, "Failed to open codec for stream #%u\n", video_stream);
return -1;
}
/* open the file to dump raw data */
output_file = fopen(argv[3], "w+b");
/* actual decoding and dump the raw data */
while (ret >= 0) {
//从文件中循环读视频帧，存入packet
if ((ret = av_read_frame(input_ctx, packet)) < 0)
break;
if (video_stream == packet->stream_index)
//解码packet，写文件
ret = decode_write(decoder_ctx, packet);
av_packet_unref(packet);
}
//冲洗解码器
/* flush the decoder */
ret = decode_write(decoder_ctx, NULL);
if (output_file)
fclose(output_file);
av_packet_free(&packet);
avcodec_free_context(&decoder_ctx);
avformat_close_input(&input_ctx);
av_buffer_unref(&hw_device_ctx);
return 0;
}
|
