ffmpeg將音頻比特率上限爲128kb/s

我想將文件上轉換爲256kb/s。（我知道我失去的質量和所有，我知道我真的要上變頻一個64KB/S => 256KB/s）的ffmpeg將音頻比特率上限爲128kb/s

命令我使用

ffmpeg -i "Same Love.m4a" -acodec libfaac "Same Love.m4a" -b:a 256kb \ 
    -loglevel debug

我有使用了我能想到的所有組合，而ffmpeg只會將上轉換爲128kbs！

這裏是我的日誌輸出的

 
$ ffmpeg -i "Same Love.m4a" -acodec libfaac "ready_to_import_to_itunes/Same Love.m4a" -b:a 256kb -loglevel debug 
ffmpeg version 1.0 Copyright (c) 2000-2012 the FFmpeg developers 
    built on Oct 12 2012 12:31:30 with Apple clang version 4.1 (tags/Apple/clang-421.11.66) (based on LLVM 3.1svn) 
    configuration: --prefix=/usr/local/Cellar/ffmpeg/1.0 --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --cc=cc --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid 
    libavutil  51. 73.101/51. 73.101 
    libavcodec  54. 59.100/54. 59.100 
    libavformat 54. 29.104/54. 29.104 
    libavdevice 54. 2.101/54. 2.101 
    libavfilter  3. 17.100/3. 17.100 
    libswscale  2. 1.101/2. 1.101 
    libswresample 0. 15.100/0. 15.100 
    libpostproc 52. 0.100/52. 0.100 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc6ab006600] Format mov,mp4,m4a,3gp,3g2,mj2 probed with size=2048 and score=100 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc6ab006600] ISO: File Type Major Brand: mp42 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc6ab006600] File position before avformat_find_stream_info() is 30844 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc6ab006600] All info found 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc6ab006600] File position after avformat_find_stream_info() is 31216 
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'Same Love.m4a': 
    Metadata: 
    major_brand  : mp42 
    minor_version : 0 
    compatible_brands: mp42isom3gp63g2a3gp4 
    creation_time : 2012-08-11 09:56:26 
    Duration: 00:05:18.71, start: 0.000000, bitrate: 64 kb/s 
    Stream #0:0(und), 1, 1/44100: Audio: aac (mp4a/0x6134706D), 44100 Hz, stereo, s16, 64 kb/s 
    Metadata: 
     creation_time : 2012-08-11 09:56:26 
     handler_name : soun 
[abuffer @ 0x7fc6aac0e560] Setting entry with key 'time_base' to value '1/44100' 
[abuffer @ 0x7fc6aac0e560] Setting entry with key 'sample_rate' to value '44100' 
[abuffer @ 0x7fc6aac0e560] Setting entry with key 'sample_fmt' to value 's16' 
[abuffer @ 0x7fc6aac0e560] Setting entry with key 'channel_layout' to value '0x3' 
[graph 0 input from stream 0:0 @ 0x7fc6aac0e660] tb:1/44100 samplefmt:s16 samplerate:44100 chlayout:0x3 
[aformat @ 0x7fc6aac0eba0] Setting entry with key 'sample_fmts' to value 's16' 
[aformat @ 0x7fc6aac0eba0] Setting entry with key 'channel_layouts' to value '0x4,0x3,0x7,0x107,0x37,0x3f' 
Output #0, ipod, to 'ready_to_import_to_itunes/Same Love.m4a': 
    Metadata: 
    major_brand  : mp42 
    minor_version : 0 
    compatible_brands: mp42isom3gp63g2a3gp4 
    encoder   : Lavf54.29.104 
    Stream #0:0(und), 0, 1/44100: Audio: aac (mp4a/0x6134706D), 44100 Hz, stereo, s16, 128 kb/s 
    Metadata: 
     creation_time : 2012-08-11 09:56:26 
     handler_name : soun 
Stream mapping: 
    Stream #0:0 -> #0:0 (aac -> libfaac) 
Press [q] to stop, [?] for help 
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x7fc6ab006600] demuxer injecting skip 1024 
[aac @ 0x7fc6ab02f600] skip 2048 samples due to side data 
[aac @ 0x7fc6ab02f600] skip whole frame, skip left: 0 
EOF on sink link output stream 0:0:default.28.0kbits/s 
No more output streams to write to, finishing. 
size= 5028kB time=00:05:18.71 bitrate= 129.2kbits/s 
video:0kB audio:4974kB subtitle:0 global headers:0kB muxing overhead 1.093817% 
[AVIOContext @ 0x7fc6aac0ca20] Statistics: 2580581 bytes read, 0 seeks

我認爲的情況是，ffmpeg的決定真的是有從去256K沒有 benifit所以帽它在128

如何強制它以指定的比特率輸出文件？（我曾嘗試與MP3也和samething發生）

來源

2013-05-01 Andrew Burns

ffmpeg -i 'Same Love.m4a' -acodec libfaac -b:a 256k 'Same Love-256.m4a'

選項必須出現以前，他們的影響，我提出-b:a
文件也實在是256k不256kb

來源

2013-05-01 18:16:34

由於'libfaac'不支持真正的CBR，比特率仍然不會是256kb/s。如果你需要，你可以使用'libfdk_aac'（它也有更高的質量）。 – mark4o 2013-05-01 19:48:36

ffmpeg將音頻比特率上限爲128kb/s

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