CODEWITHSUNDEEP
c++ffmpegcodec
david
david

Reputation: 292

C++ FFmpeg pick codec from system

I'm currently setting up my output context for creating .avi like this:

avformat_alloc_output_context2(&outContext, NULL, NULL, "out.avi");
if (!outContext)
    die("Could not allocate output context");

However, the resulting video quality is very unpleasant. As such, I'd like to be able to fetch the installed codecs on the system and use one of them in avformat_alloc_output_context2. Similar to below:

Video codec picker

So I guess my two questions are:

  1. How do I create a list (array) containing the installed codecs (as above)?
  2. How do I use one of them in the output container?

If possible, I'd also like to be able to modify output quality (0%-100%) and open the codec configuration window.

Upvotes: 1

Views: 2861

Answers (1)

Gigone Lee
Gigone Lee

Reputation: 404

First, make your map with string(or whatever) with AVCodecID, like this : 

 std::map<string, AVCodecID> _codecList;
 _codecList["h264"] = AV_CODEC_ID_H264;
 _codecList["mpeg4"] = AV_CODEC_ID_MPEG4;
 ....

Note that FFmpeg does not provide information that which codec is available in what container so you should validate yourself. but you can reference following link(at least it is officlal) : https://en.wikipedia.org/wiki/Comparison_of_video_container_formats

Next thing to do is that find encoder by name, or AVCodecID in following code : 

avcodec_find_encoder_by_name("libx264");
avcodec_find_encoder(AV_CODEC_ID_H264);

Both are return AVCodec* so you can use this when calling avformat_new_stream(), like this : 

AVCodecID codec_id = (_codecList.find("h264") != _codecList.end()) ? 
                           _codecList.find("h264") : AV_CODEC_ID_NONE;
if(codec_id == AV_CODEC_ID_NONE) 
{
    return -1;
}

AVCodec* encoder = avcodec_find_encoder(codec_id);
// or you can just get it from avcodec_find_encoder_by_name("libx264");

AVStream* newStream = avformat_new_stream(avFormatContext, encoder);

Thre are so many things when determining video quality. x264, especially has more options. In this case, you can list it by crf value or bitrate things(you can't use both option). You can determine it with AVCodecContext.

AVCodecContex* codec_ctx = newStream->codec;
codec_ctx->bitrate = 1000000 // 1MB
// codec_ctx->qmin = 18;
// codec_ctx->qmin = 31;

Once you done, open it with avcodec_open2

 avcodec_open2(avFormatContext, encoder, NULL);

And Don't forget to close when you release it.

 avcodec_close(avFormatContext);

There is much to do when you creating your own output stream. If you have deeper experience with it, i think that this answer will be enough.

But If you don't have much experience with FFmpeg, you can find my full example in here(https://github.com/sorrowhill/FFmpegTutorial)

Upvotes: 2

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