A minimal example to show how to decode and extract frames using NDK AMediaCodec

minimal_amedia_codec.cpp

// Deconding a h264 video stream... There are a few caveats which can cause some confusion.
// 1. 15 frames of 0 need flushing before we actually start pogressing.
// 2. Frames are extracted in chunks of 4 and appear in a swizzled order 4, 2, 1, 3,
// 3. The order seems consistent in blocks of 4, with the frames increasing from the middle entry rotating anti-clockwise.
// 4. Care needs to be taken when using frame numbers or timestamps to flag AMEDIACODEC_BUFFER_FLAG_END_OF_STREAM
//    Otherwise the decode may skip 4 frames (as the final frame will be delivered as the first in a block of 4).

// Havent experimented much yet but the blocks of 4 can also appear as blocks of 5, this may be due to frquency of keyframes

// tight loop will extract and decode all video frames
for(;;) {
    // the -1 blocks, this is intended to be called on a background thread, waits until we have an available input buffer
    s32 inputID = AMediaCodec_dequeueInputBuffer(m_codec, -1);

    // extract data into the input buffer
    size_t size = 0;
    u8 *input = AMediaCodec_getInputBuffer(m_codec, inputID, &size);
    auto sampleSize = AMediaExtractor_readSampleData(m_extractor, input, size);
    
    // conversion timestamp to frame, if you need it
    u64 sampleTimestamp = AMediaExtractor_getSampleTime(m_extractor);
    u32 currentFrame = round(((sampleTimestamp * m_frameRate) / 1000.0f) / 1000.0f);
    FW_LOG_CONSOLE("Extracted Sample Timestamp: %i : %i\n", sampleTimestamp, currentFrame);
  
    // queue input buffer to be decoded
    AMediaCodec_queueInputBuffer(m_codec, inputID, 0, sampleSize, sampleTimestamp, 0);

    // check if a frame has been decoded and be dequed.
    AMediaCodecBufferInfo info;
    s32 outputID = AMediaCodec_dequeueOutputBuffer(m_codec, &info, 0);
    if(outputID == AMEDIACODEC_INFO_TRY_AGAIN_LATER) {
        // if this happens you may need to deque and extract more input frames, blocking on AMediaCodec_dequeueOutputBuffer
        // can cause it to block indefinitely
        continue;
    }
    else if (outputID > 0) {
        // this will advance to the next frame, if you supply true on the end you need to render the frame
        // on another thread via ASurfaceTexture_updateTexImage, if you supply false the frame is discarded.
        // when seeking, you want to discard frames here by passing false.
        AMediaCodec_releaseOutputBuffer(m_codec, outputID, false);
        AMediaExtractor_advance(m_extractor);
    }
}

// Example Output
/*
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 0 : 0
Extracted Sample Timestamp: 166666 : 4
Extracted Sample Timestamp: 83333 : 2
Extracted Sample Timestamp: 41666 : 1
Extracted Sample Timestamp: 125000 : 3
Extracted Sample Timestamp: 333333 : 8
Extracted Sample Timestamp: 250000 : 6
Extracted Sample Timestamp: 208333 : 5
Extracted Sample Timestamp: 291666 : 7
Extracted Sample Timestamp: 500000 : 12
Extracted Sample Timestamp: 416666 : 10
Extracted Sample Timestamp: 375000 : 9
Extracted Sample Timestamp: 458333 : 11
Extracted Sample Timestamp: 666666 : 16
Extracted Sample Timestamp: 583333 : 14
Extracted Sample Timestamp: 541666 : 13
Extracted Sample Timestamp: 625000 : 15
Extracted Sample Timestamp: 833333 : 20
Extracted Sample Timestamp: 750000 : 18
Extracted Sample Timestamp: 708333 : 17
Extracted Sample Timestamp: 791666 : 19
Extracted Sample Timestamp: 1000000 : 24
Extracted Sample Timestamp: 916666 : 22
Extracted Sample Timestamp: 875000 : 21
Extracted Sample Timestamp: 958333 : 23
Extracted Sample Timestamp: 1166666 : 28
Extracted Sample Timestamp: 1083333 : 26
Extracted Sample Timestamp: 1083333 : 26
Extracted Sample Timestamp: 1041666 : 25
Extracted Sample Timestamp: 1125000 : 27
Extracted Sample Timestamp: 1333333 : 32
Extracted Sample Timestamp: 1250000 : 30
Extracted Sample Timestamp: 1208333 : 29
Extracted Sample Timestamp: 1291666 : 31
Extracted Sample Timestamp: 1500000 : 36
Extracted Sample Timestamp: 1416666 : 34
Extracted Sample Timestamp: 1375000 : 33
Extracted Sample Timestamp: 1458333 : 35
Extracted Sample Timestamp: 1625000 : 39
Extracted Sample Timestamp: 1583333 : 38
Extracted Sample Timestamp: 1583333 : 38
Extracted Sample Timestamp: 1541666 : 37
Extracted Sample Timestamp: 1791666 : 43
Extracted Sample Timestamp: 1708333 : 41
Extracted Sample Timestamp: 1666666 : 40
Extracted Sample Timestamp: 1750000 : 42
Extracted Sample Timestamp: 2000000 : 48
Extracted Sample Timestamp: 1916666 : 46
Extracted Sample Timestamp: 1833333 : 44
Extracted Sample Timestamp: 1875000 : 45
Extracted Sample Timestamp: 1958333 : 47
Extracted Sample Timestamp: 2208333 : 53
Extracted Sample Timestamp: 2125000 : 51
Extracted Sample Timestamp: 2041666 : 49
Extracted Sample Timestamp: 2083333 : 50
Extracted Sample Timestamp: 2166666 : 52
Extracted Sample Timestamp: 2416666 : 58
Extracted Sample Timestamp: 2333333 : 56
Extracted Sample Timestamp: 2250000 : 54
Extracted Sample Timestamp: 2291666 : 55
Extracted Sample Timestamp: 2375000 : 57
Extracted Sample Timestamp: 2625000 : 63
Extracted Sample Timestamp: 2541666 : 61
Extracted Sample Timestamp: 2458333 : 59
Extracted Sample Timestamp: 2500000 : 60
Extracted Sample Timestamp: 2583333 : 62
Extracted Sample Timestamp: 2833333 : 68
Extracted Sample Timestamp: 2750000 : 66
Extracted Sample Timestamp: 2666666 : 64
Extracted Sample Timestamp: 2708333 : 65
Extracted Sample Timestamp: 2791666 : 67
Extracted Sample Timestamp: 3000000 : 72
Extracted Sample Timestamp: 2916666 : 70
Extracted Sample Timestamp: 2875000 : 69
Extracted Sample Timestamp: 2958333 : 71
Extracted Sample Timestamp: 3083333 : 74
Extracted Sample Timestamp: 3041666 : 73
Extracted Sample Timestamp: 3291666 : 79
Extracted Sample Timestamp: 3208333 : 77
Extracted Sample Timestamp: 3125000 : 75
Extracted Sample Timestamp: 3166666 : 76
Extracted Sample Timestamp: 3250000 : 78
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
Extracted Sample Timestamp: -1 : -1
*/