上次说到如果音频帧的声道设置为0时，在推流写帧时会报错（参见JavaCV音频推流报错：org.bytedeco.javacv.FrameRecorder$Exception: No audio output stream (Is audioChannels > 0 and has start() been called?) ），实际上，如果声道设置的值 > 2，也会报错：

Exception in thread "main" org.bytedeco.javacv.FrameRecorder$Exception: avcodec_open2() error -22: Could not open audio codec.
    at org.bytedeco.javacv.FFmpegFrameRecorder.startUnsafe(FFmpegFrameRecorder.java:791)
    at org.bytedeco.javacv.FFmpegFrameRecorder.start(FFmpegFrameRecorder.java:384)
    at com.lxy.service.SubtitleMix.main(SubtitleMix.java:52)
Input #0, matroska,webm, from 'E:\BaiduNetdiskDownload\testout.mkv':
  Metadata:
    title           : 天下足球网 http://www.txzqw.cc
    ENCODER         : Lavf58.39.101
  Duration: 00:01:11.11, start: 0.000000, bitrate: 2485 kb/s
    Stream #0:0: Video: h264 (High), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 25 fps, 25 tbr, 1k tbn, 50 tbc (default)
    Metadata:
      ENCODER         : Lavc58.73.102 libx264
      DURATION        : 00:01:09.243000000
    Stream #0:1: Audio: vorbis, 48000 Hz, 5.1, fltp (default)
    Metadata:
      ENCODER         : Lavc58.73.102 libvorbis
      DURATION        : 00:01:09.331000000
    Stream #0:2: Subtitle: ass
    Metadata:
      ENCODER         : Lavc58.73.102 ssa
      DURATION        : 00:01:11.113000000
[libx264 @ 000000001bb89a80] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 000000001bb89a80] profile High, level 3.1, 4:2:0, 8-bit
[libx264 @ 000000001bb89a80] 264 - core 157 - H.264/MPEG-4 AVC codec - Copyleft 2003-2018 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
[libmp3lame @ 000000001ba83540] Specified channel layout '2.1' is not supported

 

　　根据上面的异常堆栈，定位到这里：

                    if ((ret = avcodec.avcodec_open2(this.audio_c, this.audio_codec, options)) < 0) {
                        this.releaseUnsafe();
                        avutil.av_dict_free(options);
                        throw new Exception("avcodec_open2() error " + ret + ": Could not open audio codec.");
                    }

 

　　至于avcodec_open2里面是啥，那就不得而知了：

public static native int avcodec_open2(AVCodecContext var0, @Const AVCodec var1, @ByPtrPtr AVDictionary var2);

 

　　真要想了解，就得扒FFMPEG的源码了。