CODEWITHSUNDEEP
audioffmpeglibavcodeclibavlibavformat
Dan
Dan

Reputation: 1338

How can I determine if a codec / container combination is compatible with FFmpeg?

I'm looking at re-muxing some containers holding audio and video such that I extract the best, first audio stream, and store it in a new container where e.g. only the audio stream is present.

The output context for FFmpeg is created like so:

AVFormatContext* output_context = NULL;
avformat_alloc_output_context2( &output_context, NULL, "mp4", NULL );

I have a shortlist of acceptable outputs, e.g. MP4, M4A, etc … essentially those that are readable by Apple's Audio File Services:

kAudioFileAIFFType              = 'AIFF',
kAudioFileAIFCType              = 'AIFC',
kAudioFileWAVEType              = 'WAVE',
kAudioFileSoundDesigner2Type    = 'Sd2f',
kAudioFileNextType              = 'NeXT',
kAudioFileMP3Type               = 'MPG3',   // mpeg layer 3
kAudioFileMP2Type               = 'MPG2',   // mpeg layer 2
kAudioFileMP1Type               = 'MPG1',   // mpeg layer 1
kAudioFileAC3Type               = 'ac-3',
kAudioFileAAC_ADTSType          = 'adts',
kAudioFileMPEG4Type             = 'mp4f',
kAudioFileM4AType               = 'm4af',
kAudioFileM4BType               = 'm4bf',
kAudioFileCAFType               = 'caff',
kAudioFile3GPType               = '3gpp',
kAudioFile3GP2Type              = '3gp2',
kAudioFileAMRType               = 'amrf'

My question is this : is there an easy API in FFmpeg that can be leveraged to choose a compatible output container given the codec the audio stream is in?

Upvotes: 5

Views: 2867

Answers (3)

RainerMtb
RainerMtb

Reputation: 366

the ffmpeg API has changed since, enumerating all containers and codecs can be done now like

void enumerate() {
    // enumerate all codecs and put into list
    std::vector<const AVCodec*> encoderList;

    void* codecState = nullptr; //start with null
    const AVCodec* codec = av_codec_iterate(&codecState);
    while (codec) {
        encoderList.push_back(codec);
        codec = av_codec_iterate(&codecState);
    }

    // enumerate all containers available for muxing
    void* muxerState = nullptr;
    const AVOutputFormat* ofmt = av_muxer_iterate(&muxerState);
    while (ofmt) {
        std::set<std::string> codecNames;
        for (auto codec : encoderList) {
            // check if codec can be used in this container
            if (avformat_query_codec(ofmt, codec->id, FF_COMPLIANCE_NORMAL) == 1) {
                // check for audio codecs here
                if (avcodec_get_type(codec->id) == AVMEDIA_TYPE_AUDIO) {
                    codecNames.insert(avcodec_get_name(codec->id));
                }
            }
        }
        // print unique format and codec names
        for (auto& codecName : codecNames) {
            std::printf("format '%s' codec '%s'\n", ofmt->name, codecName.c_str());
        }
        // get next format
        ofmt = av_muxer_iterate(&muxerState);
    }
}

Upvotes: 0

Bim
Bim

Reputation: 1068

There's a dynamic approach to that problem. This enumerates the codecs for each container, but you also get the inverse: 

// enumerate all codecs and put into list
std::vector<AVCodec*> encoderList;
AVCodec * codec = nullptr;
while (codec = av_codec_next(codec))
{
    // try to get an encoder from the system
    auto encoder = avcodec_find_encoder(codec->id);
    if (encoder)
    {
        encoderList.push_back(encoder);
    }
}
// enumerate all containers
AVOutputFormat * outputFormat = nullptr;
while (outputFormat = av_oformat_next(outputFormat))
{
    for (auto codec : encoderList)
    {
        // only add the codec if it can be used with this container
        if (avformat_query_codec(outputFormat, codec->id, FF_COMPLIANCE_STRICT) == 1)
        {
            // add codec for container
        }
    }
}

If you just want specific containers or codecs you can use a whitelist with their name or id fields and use that when enumerating.

Upvotes: 5

Gyan
Gyan

Reputation: 93261

For each individual muxer, there is usually a codec tag writing function.That function will check against a list in another source file or work through a switch statement in the same. There is no central roster or container-matching utility function. Your best bet is to identify the codec id in libavcodec/allcodecs.c and then grep in libavformat/ for that ID, particularly within files suffixed with enc e.g. matroskaenc.c.

Upvotes: 1

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