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• Big difference in wav file created from mp3 using ffmpeg versus Audacity

  16 octobre 2020, par MJLerxst

  I need to convert mp3 to wav files that will then be used by Python script. (The script analyzes the wav file data in the form of numpy arrays for each channel.) That all works fine. To get the wav, I first used Audacity "by hand" and opened the mp3, then used "Export as WAV". All good, but, I now need to automate this and avoid using Audacity. So I modified my Python script to first run ffmpeg to do the conversion, using :

  


  subprocess.call(["ffmpeg -i", mp3filename, wavfilename])


  


  Looking at the resulting wavfilename.wav data, I find it is totally different from what is in the Audacity-produced file. I verified that both approaches are using PCM 16-bit unsigned little endian, same sample rate, etc.

  


  Now, if I take that ffmpeg-produced wav file, open it with Audacity, and then "export as WAV", it will produce a 3rd wav that works just fine, and looks identical to the one that I created with Audacity in the first place - and when I say identical, I mean that I compare the numpy arrays element by element, and they line right up, whereas the ffmpeg data does not correlate to the Audacity data at all.

  


  I am using the very latest ffmpeg, ffmpeg version N-99557-g6bdfea8d4b with Lavf58.62.100. Audacity is 2.3.2. I have tried using pydub also but that gives the same results as ffmpeg.

  


  Clearly, Audacity is doing something differently when it exports the wav, and even though the ffmpeg data looks very different in Python, Audacity plays it just fine - so it is also able to correctly account for whatever it is that ffmpeg did when it made the wav file. I would simply like to get ffmpeg to emulate what Audacity does. Any advice or insight is greatly appreciated.

  


• What is the difference between "location" and "location-eng" metadata of a MP4 file ?

  10 décembre 2020, par Weihang Jian

  I am trying to retrieve GPS information from media files using ffprobe, for example :

  


  $ ffprobe -v quiet -show_format sample.mp4
[FORMAT]
filename=sample.mp4
nb_streams=2
nb_programs=0
format_name=mov,mp4,m4a,3gp,3g2,mj2
format_long_name=QuickTime / MOV
start_time=0.000000
duration=4.293000
size=11888152
bit_rate=22153556
probe_score=100
TAG:major_brand=mp42
TAG:minor_version=0
TAG:compatible_brands=isommp42
TAG:creation_time=2020-09-20T11:33:49.000000Z
TAG:location=+25.0731+121.3663/
TAG:location-eng=+25.0731+121.3663/
TAG:com.android.version=10
TAG:com.android.manufacturer=Google
TAG:com.android.model=Pixel
[/FORMAT]


  


  We can see that there are 2 tags that look like ISO6709 representations, location and location-eng.

  


  And here are my questions :

  


  

  1. What is the difference between location and location-eng ? It looks like they are always the same. Why do we need 2 different keys with same the value ?

  


  2. Are location and location-eng really in ISO6709 representations ? Is there any specification or standard I can refer to ?

  


  


  I would really appreciate your help.

  


• Difference between use subprocess.Popen() and run the command in shell mannually ? [duplicate]

  6 février 2021, par hu chenlin

  import subprocess
ffmpeg_params=['ffmpeg', '-y', '-i', 'http://cache.m.iqiyi.com/mus/235133201/2af150aebb98276a80d52513fb91fbc8/afbe8fd3d73448c9/0/20210115/1f/c5/cda301a0e8339c4cbcc89a4e9a6dafac.m3u8?qd_originate=tmts_py&tvid=1694459300&bossStatus=0&qd_vip=0&px=&src=3_31_312&prv=&previewType=&previewTime=&from=&qd_time=1612598784271&qd_p=6011968c&qd_asc=d0d83b774212c40885a78123935cf7d4&qypid=1694459300_04022000001000000000_4&qd_k=7b1dacf9d318a810bd201e367ef98196&isdol=0&code=2&ff=f4v&iswb=0&qd_s=otv&vf=bb7741a4e27350139427f0051c641530&np_tag=nginx_part_tag', '-c', 'copy', '-bsf:a', 'aac_adtstoasc', '--', 'f:\\/【英语口语】我羡慕你.mp4']
b=subprocess.Popen(ffmpeg_params)


  


  Using this simple .py script I can call ffmpeg to download the video file sucessfully.

  


  However, if I run

  


  


  ffmpeg -y -i
http://cache.m.iqiyi.com/mus/235133201/2af150aebb98276a80d52513fb91fbc8/afbe8fd3d73448c9/0/20210115/1f/c5/cda301a0e8339c4cbcc89a4e9a6dafac.m3u8?qd_originate=tmts_py&tvid=1694459300&bossStatus=0&qd_vip=0&px=&src=3_31_312&prv=&previewType=&previewTime=&from=&qd_time=1612598784271&qd_p=6011968c&qd_asc=d0d83b774212c40885a78123935cf7d4&qypid=1694459300_04022000001000000000_4&qd_k=7b1dacf9d318a810bd201e367ef98196&isdol=0&code=2&ff=f4v&iswb=0&qd_s=otv&vf=bb7741a4e27350139427f0051c641530&np_tag=nginx_part_tag
-c copy -bsf:a aac_adtstoasc — f :/【英语口语】我羡慕你.mp4

  


  


  in shell, it will fail with below message :

  


  


  ffmpeg version N-90173-gfa0c9d69d3 Copyright (c) 2000-2018 the FFmpeg
developers built with gcc 7.3.0 (GCC) configuration : —enable-gpl
—enable-version3 —enable-sdl2 —enable-bzlib —enable-fontconfig —enable-gnutls —enable-iconv —enable-libass —enable-libbluray —enable-libfreetype —enable-libmp3lame —enable-libopencore-amrnb —enable-libopencore-amrwb —enable-libopenjpeg —enable-libopus —enable-libshine —enable-libsnappy —enable-libsoxr —enable-libtheora —enable-libtwolame —enable-libvpx —enable-libwavpack —enable-libwebp —enable-libx264 —enable-libx265 —enable-libxml2 —enable-libzimg —enable-lzma —enable-zlib —enable-gmp —enable-libvidstab —enable-libvorbis —enable-libvo-amrwbenc —enable-libmysofa —enable-libspeex —enable-libxvid —enable-libmfx —enable-amf —enable-cuda —enable-cuvid —enable-d3d11va —enable-nvenc —enable-dxva2 —enable-avisynth libavutil 56. 7.101 / 56. 7.101 libavcodec 58. 13.100 / 58. 13.100 libavformat 58. 10.100 /
58. 10.100 libavdevice 58. 2.100 / 58. 2.100 libavfilter 7. 12.100 / 7. 12.100 libswscale 5. 0.101 / 5. 0.101 libswresample 3. 0.101 / 3. 0.101 libpostproc 55. 0.100 /
55. 0.100 http://cache.m.iqiyi.com/mus/235133201/2af150aebb98276a80d52513fb91fbc8/afbe8fd3d73448c9/0/20210115/1f/c5/cda301a0e8339c4cbcc89a4e9a6dafac.m3u8?qd_originate=tmts_py :
Invalid data found when processing input 'tvid' is not recognized as
an internal or external command, operable program or batch file.
'bossStatus' is not recognized as an internal or external command,
operable program or batch file.

  


  


  I can use subprocess.Popen to call the ffmpeg to download the video file successfully, However, I can't directly run ffmpeg in shell with the same parameters to download the file. Why ? How can I directly run ffmpeg in shell to download the file ?