3
最近我正在編寫提供H.264流的IP攝像機的客戶端。我現在使用FFmpeg 2.1.1來解碼相機提供的流。使用FFmpeg無法解碼H.264流（Annex.B）
這裏的應用程序的一些代碼：
初始化：
private unsafe void InitFFmpeg()
{
FFmpeg.avcodec_register_all();
var codec = FFmpeg.avcodec_find_decoder(AVCodecID.AV_CODEC_ID_H264);
avcodec = (IntPtr)codec;
var ctx=FFmpeg.avcodec_alloc_context3(avcodec);
avcontext = (IntPtr)ctx;
ctx->codec = avcodec;
ctx->pix_fmt = AVPixelFormat.PIX_FMT_YUV420P;
ctx->flags2 |= 0x00008000;//CODEC_FLAG2_CHUNKS
var options = IntPtr.Zero;
int result = FFmpeg.avcodec_open2(avcontext, avcodec, ref options);
avframe = FFmpeg.av_frame_alloc();
avparser = FFmpeg.av_parser_init(AVCodecID.AV_CODEC_ID_H264);
FFmpeg.av_init_packet(ref avpacket);
inBuffer = Marshal.AllocHGlobal(300 * 1024);
}
解碼：
private void Decode(byte[] data, int size)
{
IntPtr pOut = IntPtr.Zero;
int outLen = 0;
Marshal.Copy(data, 0, inBuffer, size);
int gotPicture = 0;
var rs = FFmpeg.av_parser_parse2(avparser, avcontext, ref pOut, ref outLen, inBuffer, size, 0, 0, 0);
if (outLen <= 0 || pOut.ToInt32() <= 0)
{
//no enough data to construct a frame, return and receive next NAL unit.
return;
}
avpacket.data = pOut;
avpacket.size = outLen;
avpacket.flags |= PacketFlags.Key;
var len = FFmpeg.avcodec_decode_video2(avcontext, avframe, ref gotPicture, ref avpacket);
Console.WriteLine("avcodec_decode_video2 returned " + len);
if (gotPicture != 0)
{
//some YUV to RGB stuff
}
}
通過上面的代碼，我可以得到一些輸出，如：
NAL unit 1: resolution=1280x720, key-frame=True, size=26.
NAL unit 2: resolution=1280x720, key-frame=False, size=8.
NAL unit 3: resolution=1280x720, key-frame=False, size=97222.
NAL unit 4: resolution=1280x720, key-frame=False, size=14129.
avcodec_decode_video2 returned 1
NAL unit 5: resolution=1280x720, key-frame=False, size=12522.
NAL unit 6: resolution=1280x720, key-frame=False, size=12352.
avcodec_decode_video2 returned 1
NAL unit 7: resolution=1280x720, key-frame=False, size=12291.
NAL unit 8: resolution=1280x720, key-frame=False, size=12182.
從輸出中，我可以看到解析器可以識別攝像機發送的NAL單元，並且可以從它們構建幀。
NAL單元1至4是含SPS/PPS關鍵幀的切片，並將下列NAL單元形成正常的幀。
而且avcodec_decode_video2功能不會產生任何錯誤，只是回頭率1和gotPicture常是0
如果我清除AVCodecContext.flags2，它開始抱怨我提供的包不包含框架：
NAL unit 100: resolution=1280x720, frame-rate=0, key-frame=True, size=26.
NAL unit 101: resolution=1280x720, frame-rate=0, key-frame=False, size=8.
NAL unit 102: resolution=1280x720, frame-rate=0, key-frame=False, size=96927.
NAL unit 103: resolution=1280x720, frame-rate=0, key-frame=False, size=17149.
[h264 @ 01423440] no frame!
avcodec_decode_video2 returned -1094995529
NAL unit 104: resolution=1280x720, frame-rate=0, key-frame=False, size=12636.
NAL unit 105: resolution=1280x720, frame-rate=0, key-frame=False, size=12338.
[h264 @ 01423440] no frame!
如果我寫的原始流到一個文件，我可以使用的FFmpeg到流複用器，以MP4容器，並可以與任何播放器上播放的MP4文件。
我接收到的原始數據是一樣的東西：
00 00 00 01 67 42 00 28 E9 00 A0 0B 75 C4 80 03 6E E8 00 CD FE 60 0D 88 10 94
00 00 00 01 68 CE 31 52
00 00 00 01 65 88 81 00 06 66 36 25 11 21 2C 04 3B 81 E1 80 00 85 4B 23 9F 71...
...