Why I can't check the bit rate on some videos?

Question

I've downloaded a video from YouTube, well I've downloaded the video stream and the audio stream of a YouTube video separately. Then with this ffmpeg command ffmpeg -protocol_whitelist "file,http,https,tcp,tls" -i video.mp4 -i audio.webm -acodec copy -vcodec copy output.mkv I merged the two streams together.

Using the ffprobe -i audio.webm -show_streams -hide_banner command it gives me the bitrate of the audio file but not of the stream (in this case it's not crucial since the file is only one stream) :

Duration: 01:35:26.06, start: -0.007000, bitrate: 119 kb/s
  Stream #0:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)

But in the detailed stream informations I get after thanks to the parameter -show-streams it doesn't give me the bit rate of the stream : bit_rate=N/A

Same command with the video file :

Duration: 01:35:26.04, start: 0.000000, bitrate: 213 kb/s
   Stream #0:0(und): Video: av1 (Main) (av01 / 0x31307661), yuv420p(tv), 640x284, 0 kb/s, 24 fps, 24 tbr, 12288 tbn, 12288 tbc (default)

And again in the detailed stream informations it doesn't give me 213 for the bitrate of the stream but 21 (I don't know why) : bit_rate=21.

However when I try the same command with the mkv file that contains the audio and video streams I get that :

Duration: 01:35:26.06, start: -0.007000, bitrate: 331 kb/s
  Stream #0:0: Video: av1 (Main), yuv420p(tv), 640x284, 24 fps, 24 tbr, 1k tbn, 1k tbc (default)
  Stream #0:1(eng): Audio: opus, 48000 Hz, stereo, fltp (default)

So I get an overall bit rate but not the bitrate of each stream which is more annoying. In the detailed stream informations for both streams I have : bit_rate=N/A.

Using other tools, mediainfo for example. On the audio file (mediainfo --fullscan Ofitsery.webm) I have an overall bitrate for the file : Overall bit rate : 120 kb/s but no bitrate indicated for the audio stream. For the video file (mediainfo --fullscan Ofitsery.mp4) I have an overall bitrate : Overall bit rate : 213 kb/s and a bitrate for the video stream which is not exactly the same (on a file with only one stream) : Bit rate : 211 kb/s. But on my mkv file that contains the audio and the video stream I have an overall bitrate : Overall bit rate : 332 kb/s but no bitrate neither for the video stream nor the audio stream.

It annoys me because I'd like to check if I have bitrate loss during the file merging and I can't check the bit rate of the streams separately. Beside why are there 1 or 2 kb/s differences sometimes ?

Answer 1

For mkv files, you can use mkvpropedit —add-track-statistics-tags to add stream level data.

Answer 2

Bitrate isn't calculated from stream size, but the number is saved in file as special field/metadata. Now, the problem with ffmpeg (or rather libmatroska) and Matroska (MKV) muxer is it doesn't save such data.

If you are able, use another container - for me switching to MP4 helped. While it's in Handbrake's GitHub, there's discussion about bitrate in MKV here: https://github.com/HandBrake/HandBrake/issues/1609

PS: As I see you are into open source, I bet MP4 is not a good way, but it's the only I know. I'll be happy to find out how to add such metadata to MKV.