如何使用 FFmpeg 获得视频的本机帧速率？

Question

背景

我有一个 .mp4 视频，我需要获取视频的帧速率。使用 ffmepg（在 Linux 中）我知道我可以通过以下命令获取此信息：

ffprobe -v 0 -of compact=p=0 -select_streams 0 -show_entries stream=r_frame_rate 'MyVideoFIle.mp4'

哪个returns:

r_frame_rate=24000/1001

FFmpex

在 bash 中这样做很好，但我真正想要的是在我的 Elixir 应用程序中使用它。为此我查了一下ffmpex.

首先我尝试使用 FFprobe:

> FFprobe.format("Devil May Cry 5 Bury the Light LITTLE V COVER.mp4")

{:ok,
 %{
   "bit_rate" => "611784",
   "duration" => "482.999000",
   "filename" => "Devil May Cry 5 Bury the Light LITTLE V COVER.mp4",
   "format_long_name" => "QuickTime / MOV",
   "format_name" => "mov,mp4,m4a,3gp,3g2,mj2",
   "nb_programs" => 0,
   "nb_streams" => 2,
   "probe_score" => 100, 
   "size" => "36936415",
   "start_time" => "0.000000",
   "tags" => %{
     "compatible_brands" => "isomiso2avc1mp41",
     "encoder" => "Lavf58.19.102",
     "major_brand" => "isom",
     "minor_version" => "512"
   }
 }}

这给了我一些信息，但不是帧速率。

我的下一个尝试是使用命令选项：

command = 
  FFmpex.new_command() 
  |> add_input_file("Devil May Cry 5 Bury the Light LITTLE V COVER.mp4") 
  |> add_video_option(???)

但这里的问题是我无法在文档中找到获取本机帧速率所需的视频选项。我只找到 vframe 用于设置视频帧率。

问题

如何使用 ffmpex 获取视频的原生 fps？

Answer 1

我不使用 FFmpex，但通过快速查看 Github 上的源代码：

看到第 71 行 ffmpex/lib/ffprobe.ex 是设置传递给 FFprobe 的选项：

cmd_args = ["-v", "quiet", "-print_format", "json", "-show_format", file_path]

所以也许将该行调整为：

cmd_args = ["-v", "quiet", "-print_format", "json", "-show_format", "-show_entries stream=r_frame_rate", file_path]

有可能上面写成：

cmd_args = ["-v", "quiet", "-print_format", "json", "-show_format", "-show_entries", "stream=r_frame_rate", file_path]

Answer 2

按照@VC.One的建议并查看源代码，我找到了FFprobe.streams("filename").

此函数将 return 流列表及其 avg_frame_rate，这是来自 shell 的本机命令所做的：

FFprobe.streams("Devil May Cry 5 Bury the Light LITTLE V COVER.mp4")
{:ok,
 [
   %{
     "refs" => 1,
     "avg_frame_rate" => "24000/1001",
     "level" => 31,
     "nb_frames" => "11579",
     "is_avc" => "true",
     "coded_height" => 720,
     "index" => 0,
     "display_aspect_ratio" => "16:9",
     "r_frame_rate" => "24000/1001",
     "nal_length_size" => "4",
     "has_b_frames" => 1,
     "height" => 720,
     "time_base" => "1/24000",
     "codec_time_base" => "1001/48000",
     "color_transfer" => "bt709",
     "color_space" => "bt709",
     "codec_tag_string" => "avc1",
     "pix_fmt" => "yuv420p",
     "bits_per_raw_sample" => "8",
     "bit_rate" => "478071",
     "codec_tag" => "0x31637661",
     "profile" => "Main",
     "sample_aspect_ratio" => "1:1",
     "chroma_location" => "left",
     "color_primaries" => "bt709",
     "coded_width" => 1280,
     "width" => 1280,
     "codec_type" => "video",
     "codec_long_name" => "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
     "start_time" => "0.000000",
     "duration" => "482.940792",
     "duration_ts" => 11590579,
     "codec_name" => "h264",
     "start_pts" => 0,
     "tags" => %{
       "handler_name" => "ISO Media file produced by Google Inc.",
       "language" => "und"
     },
     "color_range" => "tv",
     "disposition" => %{
       "attached_pic" => 0,
       "clean_effects" => 0,
       "comment" => 0,
       "default" => 1,
       "dub" => 0,
       "forced" => 0,
       "hearing_impaired" => 0,
       "karaoke" => 0,
       "lyrics" => 0,
       "original" => 0,                                                                                                                                                                      
       ...                                                                                                                                                                                   
     }
   },
   %{
     "avg_frame_rate" => "0/0",
     "bit_rate" => "127999",
     "bits_per_sample" => 0,
     "channel_layout" => "stereo",
     "channels" => 2,
     "codec_long_name" => "AAC (Advanced Audio Coding)",
     "codec_name" => "aac",
     "codec_tag" => "0x6134706d",
     "codec_tag_string" => "mp4a",
     "codec_time_base" => "1/44100",
     "codec_type" => "audio",
     "disposition" => %{
       "attached_pic" => 0,
       "clean_effects" => 0,
       "comment" => 0,
       "default" => 1,
       "dub" => 0,
       "forced" => 0,
       "hearing_impaired" => 0,
       "karaoke" => 0,
       "lyrics" => 0,
       "original" => 0,
       "timed_thumbnails" => 0,
       "visual_impaired" => 0
     },
     "duration" => "482.998277",
     "duration_ts" => 21300224,
     "index" => 1,
     "max_bit_rate" => "127999",
     "nb_frames" => "20801",
     "profile" => "LC",
     "r_frame_rate" => "0/0",
     "sample_fmt" => "fltp",
     "sample_rate" => "44100",
     "start_pts" => 0,
     "start_time" => "0.000000",
     "tags" => %{
       "handler_name" => "ISO Media file produced by Google Inc.",
       "language" => "und"
     },
     "time_base" => "1/44100"
   }
 ]}

这回答了我的问题。 FFprobe.format/1 从来都不是解决方案，它是 FFprobe.streams/1!

如何使用 FFmpeg 获得视频的本机帧速率？

How to get native frame rate of vide with FFmpex?

video

ffmpeg

elixir

背景

FFmpex

问题