How to get native frame rate of video with FFmpex?

Questions / Help
1

Background

I have an .mp4 video and I need to get the video’s frame rate. Using ffmepg (in Linux) I know I can get this information via the following command:

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

Which returns:

r_frame_rate=24000/1001

FFmpex

Doing this in bash is fine, but what I really want is to use it in my Elixir application. To this end I found out about ffmpex.

First I tried using 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"
   }
 }}

Which gives me some information, but not the frame rate.

My next tentative was to use the command options:

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

But the problem here is that I can’t find in the documentation the video option I need to get the native frame rate. I only found vframe which is used to set the video frame rate.

Question

  • How can I get the native fps of a video using ffmpex?
2

You already got the framerate 24000 / 1001 = ~23.976. 24000 divided by 1001.

3

I got the frame rate using the bash. I want it using the Elixir application so I can use code that does it for me.

4

By looking at the source code, I was able to find FFprobe.streams("filename").

This function will return a list of streams with their avg_frame_rate, which is what the native command from the shell was doing:

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"
   }
 ]}

This answers my question. FFprobe.format/1 was never the solution, it was FFprobe.streams/1!

1 Like
5

It seems that I didn’t fully understand your question but you can just output as json from ffprobe with -print_format json then decode that in Elixir

1 Like
6

The idea of my question was to use the Elixir library to achieve this, not the command line. In theory I could use System.cmd to directly send bash commands to the machine and then get the output as JSON format, but that was not the intent of the question.

Thanks for trying to help though!

1 Like
7

What is totally amazing about this command is that it works on a file on S3:

ffprobe -v quiet -print_format json -show_streams https://bucket.s3.region.amazonaws.com/file.mp4

1 Like