Question

我正在使用通过Homebrew安装的libav 9.6。

$ avprobe -version
avprobe version 9.6, Copyright (c) 2007-2013 the Libav developers
  built on Jun  8 2013 02:44:19 with Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)
avprobe 9.6
libavutil     52.  3. 0 / 52.  3. 0
libavcodec    54. 35. 0 / 54. 35. 0
libavformat   54. 20. 3 / 54. 20. 3
libavdevice   53.  2. 0 / 53.  2. 0
libavfilter    3.  3. 0 /  3.  3. 0
libavresample  1.  0. 1 /  1.  0. 1
libswscale     2.  1. 1 /  2.  1. 1

即使采样率显示在命令行输出的标准输出中，-show_format选项也不会显示音频文件的采样率信息。

这是BASH终端输出：

$ avprobe  -v verbose -show_format -of json  sample.gsm
avprobe version 9.6, Copyright (c) 2007-2013 the Libav developers
  built on Jun  8 2013 02:44:19 with Apple LLVM version 4.2 (clang-425.0.24)
(based on LLVM 3.2svn)
  configuration: --prefix=/usr/local/Cellar/libav/9.6 --enable-shared
--enable-pthreads --enable-gpl --enable-version3 --enable-nonfree
--enable-hardcoded-tables --enable-avresample --enable-vda --enable-gnutls
--enable-runtime-cpudetect --disable-indev=jack --cc=cc --host-cflags=
--host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame
--enable-libxvid --enable-avplay
  libavutil     52.  3. 0 / 52.  3. 0
  libavcodec    54. 35. 0 / 54. 35. 0
  libavformat   54. 20. 3 / 54. 20. 3
  libavdevice   53.  2. 0 / 53.  2. 0
  libavfilter    3.  3. 0 /  3.  3. 0
  libavresample  1.  0. 1 /  1.  0. 1
  libswscale     2.  1. 1 /  2.  1. 1
[gsm @ 0x7f8012806600] Estimating duration from bitrate, this may be inaccurate
Input #0, gsm, from 'sample.gsm':
  Duration: 00:03:52.32, start: 0.000000, bitrate: 13 kb/s
    Stream #0.0: Audio: gsm, 8000 Hz, mono, s16, 13 kb/s
{  "format" : {
    "filename" : "sample.gsm",
    "nb_streams" : 1,
    "format_name" : "gsm",
    "format_long_name" : "raw GSM",
    "start_time" : "0.000000",
    "duration" : "232.320000",
    "size" : "383328.000000",
    "bit_rate" : "13200.000000"
  }}

和python代码示例：

>>> filename = 'sample.gsm'
>>> result = subprocess.check_output(['avprobe', '-show_format', '-of',
'json', filename])
avprobe version 9.6, Copyright (c) 2007-2013 the Libav developers
  built on Jun  8 2013 02:44:19 with Apple LLVM version 4.2
(clang-425.0.24) (based on LLVM 3.2svn)
[gsm @ 0x7fe0b1806600] Estimating duration from bitrate, this may be
inaccurate
Input #0, gsm, from 'sample.gsm':
  Duration: 00:03:52.32, start: 0.000000, bitrate: 13 kb/s
    Stream #0.0: Audio: gsm, 8000 Hz, mono, s16, 13 kb/s
>>> print result
{  "format" : {
    "filename" : "sample.gsm",
    "nb_streams" : 1,
    "format_name" : "gsm",
    "format_long_name" : "raw GSM",
    "start_time" : "0.000000",
    "duration" : "232.320000",
    "size" : "383328.000000",
    "bit_rate" : "13200.000000"
}}

所以我知道采样率可能是特定于流的显示，要显示在-show_format选项结果中。但是，没有任何其他选项可以检测特定音频流的采样率，即使在重新编码时也可以使用-ar进行设置。

我向libav提交了a ticket但我很好奇是否还有其他方法可以从libav探测工具中提取采样率。我事先赞赏答案。

PS：在这种情况下，ffmpeg（ffprobe）的上游项目也是同样的问题。

Answer 1

-show_format显示容器级信息 - 即适用于所有流的内容。采样率是单个流的属性，因此-show_format不显示它是完全正常的。您需要使用-show_streams。

Answer 2

我发现json库可以将ffprobe的输出解析为字典，并详细说明了将信息存储在python中的代码。这是一个执行此操作并根据需要打印媒体信息的功能：

from json import loads
from subprocess import check_output

def get_media_info(filename, print_result=True):
    """
    Returns:
        result = dict with audio info where:
        result['format'] contains dict of tags, bit rate etc.
        result['streams'] contains a dict per stream with sample rate, channels etc.
    """
    result = check_output(['ffprobe',
                            '-hide_banner', '-loglevel', 'panic',
                            '-show_format',
                            '-show_streams',
                            '-of',
                            'json', filename])

    result = json.loads(result)

    if print_result:
        print('\nFormat')

        for key, value in result['format'].items():
            print('   ', key, ':', value)

        print('\nStreams')
        for stream in result['streams']:
            for key, value in stream.items():
                print('   ', key, ':', value)

        print('\n')

    return result

如何用avprobe / ffprobe检测音频采样率？

2 个答案: