我使用ffmpeg 3进行视频格式转换，当我使用命令行模式时它工作正常，但是当我调用libav *库时，我遇到音频质量损失问题（有很多噪音）在音频中。）
以下是两个文件：
mv.webm - original file
mv2.mp4 converted with libarary , a lot of noises
以下是mv.webm的探测信息：
$ ffprobe mv.webm
ffprobe version N-79826-g64fd62d Copyright (c) 2007-2016 the FFmpeg developers
built with gcc 5.3.1 (Ubuntu 5.3.1-14ubuntu2) 20160413
configuration: --prefix=/home/seaguest/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/seaguest/ffmpeg_build/include --extra-ldflags=-L/home/seaguest/ffmpeg_build/lib --enable-gpl --enable-libfdk-aac --enable-libx264 --enable-libx265 --enable-nonfree
libavutil 55. 24.100 / 55. 24.100
libavcodec 57. 39.100 / 57. 39.100
libavformat 57. 36.100 / 57. 36.100
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 45.100 / 6. 45.100
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 0.101 / 2. 0.101
libpostproc 54. 0.100 / 54. 0.100
Input #0, matroska,webm, from 'mv.webm':
Metadata:
encoder : Lavf57.36.100
Duration: 00:00:30.00, start: 0.000000, bitrate: 935 kb/s
Stream #0:0: Video: vp8, yuv420p, 640x480, SAR 1:1 DAR 4:3, 25 fps, 25 tbr, 1k tbn (default)
Stream #0:1: Audio: vorbis, 44100 Hz, stereo, fltp (default)
我检查了通过命令行模式打印的日志并调用了代码模式，设置看起来是一样的，这里是日志：
$ ffmpeg -i mv.webm -c:a aac -c:v libx264 mv.mp4
ffmpeg version N-79826-g64fd62d Copyright (c) 2000-2016 the FFmpeg developers
built with gcc 5.3.1 (Ubuntu 5.3.1-14ubuntu2) 20160413
configuration: --prefix=/home/seaguest/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/seaguest/ffmpeg_build/include --extra-ldflags=-L/home/seaguest/ffmpeg_build/lib --enable-gpl --enable-libfdk-aac --enable-libx264 --enable-libx265 --enable-nonfree
libavutil 55. 24.100 / 55. 24.100
libavcodec 57. 39.100 / 57. 39.100
libavformat 57. 36.100 / 57. 36.100
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 45.100 / 6. 45.100
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 0.101 / 2. 0.101
libpostproc 54. 0.100 / 54. 0.100
Input #0, matroska,webm, from 'mv.webm':
Metadata:
encoder : Lavf57.36.100
Duration: 00:00:30.00, start: 0.000000, bitrate: 935 kb/s
Stream #0:0: Video: vp8, yuv420p, 640x480, SAR 1:1 DAR 4:3, 25 fps, 25 tbr, 1k tbn (default)
Stream #0:1: Audio: vorbis, 44100 Hz, stereo, fltp (default)
[libx264 @ 0x3e5d880] using SAR=1/1
[libx264 @ 0x3e5d880] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0x3e5d880] profile High, level 3.0
[libx264 @ 0x3e5d880] 264 - core 148 r2643 5c65704 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - 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
[mp4 @ 0x3e2f680] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
Last message repeated 1 times
Output #0, mp4, to 'mv.mp4':
Metadata:
encoder : Lavf57.36.100
Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 640x480 [SAR 1:1 DAR 4:3], q=2-31, 25 fps, 12800 tbn (default)
Metadata:
encoder : Lavc57.39.100 libx264
Side data:
cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream #0:1: Audio: aac (LC) ([64][0][0][0] / 0x0040), 44100 Hz, stereo, fltp, 128 kb/s (default)
Metadata:
encoder : Lavc57.39.100 aac
Stream mapping:
Stream #0:0 -> #0:0 (vp8 (native) -> h264 (libx264))
Stream #0:1 -> #0:1 (vorbis (native) -> aac (native))
Press [q] to stop, [?] for help
frame= 750 fps=229 q=-1.0 Lsize= 2508kB time=00:00:30.02 bitrate= 684.5kbits/s speed=9.17x
video:2023kB audio:459kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.052857%
[libx264 @ 0x3e5d880] frame I:11 Avg QP:15.29 size: 20395
[libx264 @ 0x3e5d880] frame P:345 Avg QP:20.93 size: 4350
[libx264 @ 0x3e5d880] frame B:394 Avg QP:23.55 size: 879
[libx264 @ 0x3e5d880] consecutive B-frames: 25.2% 3.2% 33.2% 38.4%
[libx264 @ 0x3e5d880] mb I I16..4: 44.1% 32.5% 23.4%
[libx264 @ 0x3e5d880] mb P I16..4: 1.5% 3.6% 0.6% P16..4: 28.9% 11.2% 4.7% 0.0% 0.0% skip:49.5%
[libx264 @ 0x3e5d880] mb B I16..4: 0.0% 0.1% 0.0% B16..8: 27.4% 2.0% 0.4% direct: 0.8% skip:69.3% L0:40.0% L1:53.3% BI: 6.7%
[libx264 @ 0x3e5d880] 8x8 transform intra:52.6% inter:74.9%
[libx264 @ 0x3e5d880] coded y,uvDC,uvAC intra: 57.5% 68.6% 35.9% inter: 10.6% 11.9% 2.6%
[libx264 @ 0x3e5d880] i16 v,h,dc,p: 36% 42% 7% 15%
[libx264 @ 0x3e5d880] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 15% 23% 15% 6% 7% 7% 10% 7% 10%
[libx264 @ 0x3e5d880] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 20% 27% 14% 6% 8% 7% 7% 6% 6%
[libx264 @ 0x3e5d880] i8c dc,h,v,p: 46% 34% 11% 9%
[libx264 @ 0x3e5d880] Weighted P-Frames: Y:0.0% UV:0.0%
[libx264 @ 0x3e5d880] ref P L0: 63.9% 20.8% 11.2% 4.1%
[libx264 @ 0x3e5d880] ref B L0: 93.1% 6.1% 0.8%
[libx264 @ 0x3e5d880] ref B L1: 95.8% 4.2%
[libx264 @ 0x3e5d880] kb/s:552.32
[aac @ 0x3e5ec00] Qavg: 3030.804
$ ffprobe mv.mp4
ffprobe version N-79826-g64fd62d Copyright (c) 2007-2016 the FFmpeg developers
built with gcc 5.3.1 (Ubuntu 5.3.1-14ubuntu2) 20160413
configuration: --prefix=/home/seaguest/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/seaguest/ffmpeg_build/include --extra-ldflags=-L/home/seaguest/ffmpeg_build/lib --enable-gpl --enable-libfdk-aac --enable-libx264 --enable-libx265 --enable-nonfree
libavutil 55. 24.100 / 55. 24.100
libavcodec 57. 39.100 / 57. 39.100
libavformat 57. 36.100 / 57. 36.100
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 45.100 / 6. 45.100
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 0.101 / 2. 0.101
libpostproc 54. 0.100 / 54. 0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'mv.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.36.100
Duration: 00:00:30.01, start: 0.000000, bitrate: 684 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 552 kb/s, 25 fps, 25 tbr, 12800 tbn (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
Metadata:
handler_name : SoundHandler
对于呼叫代码模式：
$ go run transcode.go mv.webm mv1.mp4
# github.com/3d0c/gmf
../packet.go: In function ‘_cgo_3c42eeb63b1e_Cfunc_avcodec_decode_audio4’:
../packet.go:87:2: warning: ‘avcodec_decode_audio4’ is deprecated [-Wdeprecated-declarations]
func (this *Packet) decode(cc *CodecCtx, frame *Frame) (*Frame, bool, int, error) {
^
In file included from ../packet.go:7:0:
/home/seaguest/ffmpeg_build/include/libavcodec/avcodec.h:4685:5: note: declared here
int avcodec_decode_audio4(AVCodecContext *avctx, AVFrame *frame,
^
../packet.go: In function ‘_cgo_3c42eeb63b1e_Cfunc_avcodec_decode_video2’:
../packet.go:104:2: warning: ‘avcodec_decode_video2’ is deprecated [-Wdeprecated-declarations]
}
^
In file included from ../packet.go:7:0:
/home/seaguest/ffmpeg_build/include/libavcodec/avcodec.h:4734:5: note: declared here
int avcodec_decode_video2(AVCodecContext *avctx, AVFrame *picture,
^
[libx264 @ 0x2d82400] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0x2d82400] profile High, level 3.0
[libx264 @ 0x2d82400] 264 - core 148 r2643 5c65704 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - 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
[mp4 @ 0x2d480c0] Using AVStream.codec.time_base as a timebase hint to the muxer is deprecated. Set AVStream.time_base instead.
[mp4 @ 0x2d480c0] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
[mp4 @ 0x2d480c0] Using AVStream.codec.time_base as a timebase hint to the muxer is deprecated. Set AVStream.time_base instead.
[mp4 @ 0x2d480c0] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
$ ffprobe mv1.mp4
ffprobe version N-79826-g64fd62d Copyright (c) 2007-2016 the FFmpeg developers
built with gcc 5.3.1 (Ubuntu 5.3.1-14ubuntu2) 20160413
configuration: --prefix=/home/seaguest/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/seaguest/ffmpeg_build/include --extra-ldflags=-L/home/seaguest/ffmpeg_build/lib --enable-gpl --enable-libfdk-aac --enable-libx264 --enable-libx265 --enable-nonfree
libavutil 55. 24.100 / 55. 24.100
libavcodec 57. 39.100 / 57. 39.100
libavformat 57. 36.100 / 57. 36.100
libavdevice 57. 0.101 / 57. 0.101
libavfilter 6. 45.100 / 6. 45.100
libswscale 4. 1.100 / 4. 1.100
libswresample 2. 0.101 / 2. 0.101
libpostproc 54. 0.100 / 54. 0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'mv1.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.36.100
Duration: 00:00:30.00, start: 0.000000, bitrate: 751 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x480, 613 kb/s, 25 fps, 25 tbr, 12800 tbn (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 130 kb/s (default)
Metadata:
handler_name : SoundHandler
检查设置部分，两者的crf = 23.0（其余部分完全相同），但输出比特率不同（调用代码模式的音频有很多噪音），这怎么可能？
为什么命令行模式和使用libav *库模式设置相同但输出不同？ 如何调用libav *库进行无损视频转换？