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• How do I use ffmpeg to extract the total time of a video slice without actually producing the video slice ?

  18 juin 2022, par iChux

  


  I have a video named 'ev.mp4'. Slice the video into segments :

  


  


  # COMMAND 1
ffmpeg -i "ev.mp4" -c copy -map 0 -segment_time 15 -g 9 \
    -sc_threshold 0 -force_key_frames "expr:gte(t,n_forced*9)" \
    -reset_timestamps 1 -f segment ev-%04d.mp4

ev-0000.mp4
ev-0001.mp4
ev-0002.mp4


  


  


  Get each segment time

  


  


  # COMMAND 2
for f in ev-*.mp4;
do
    echo $f == $(ffprobe -v error -show_entries \
    format=duration -of default=noprint_wrappers=1:nokey=1 $f);
done;

ev-0000.mp4 == 17.251000
ev-0001.mp4 == 17.918000
ev-0002.mp4 == 10.444000


  


  


  I am only able to extract the duration of each sliced segment after the videos have existed in a sliced format on the hard drive e.g. ev-0000.mp4

  


  


  My question : is it possible to get the duration of each slice from COMMAND 1 such that instead of producing the sliced files, I will get the duration of each slice ?

  


• Compressing videos from a smartphone

  21 septembre 2019, par fejesjoco

  I have a Nexus 6p with the stock camera. It’s set to record at 1080p, 30fps. Here’s a 5 second sample (11 MB).

  Videos from this phone come out at about 17 Mbps on average. I tried to compress it with ffmpeg with -c:v libx264 -crf 23 -preset veryslow, the result comes out at about 5.5 MB, which is about 9 Mbps.

  I think this bitrate is a bit too much. When I look at torrent file listings, I can see high quality videos at 3 GB in size on average, and if such a movie is 90 minutes long on average, that is about 4-5 Mbps which sounds okay.

  I’m wondering, why the big difference ? I can notice that my video is noisy/grainy (which is expected from a phone), and that might reduce compressibility. I tried a few ffmpeg filters, like hqdn3d and atadenoise, but the noise mostly remained (maybe I didn’t play with it enough). Then I figured, the video is also shaky (which is also expected), and that might reduce compressibility too (and even makes temporal noise filtering less effective). I tried to stabilize it with the deshake filter, but that didn’t help either.

  I know I could just limit the bandwidth to whatever I like, but there must be a reason why ffmpeg thinks it needs a high bandwidth to maintain a certain quality, and a lower bandwidth would just decrease the quality.

  Why do these videos have such a high bitrate ? What’s the best way to compress them more while keeping or even increasing their quality ?

• Compressing videos from a smartphone

  9 novembre 2016, par fejesjoco

  I have a Nexus 6p with the stock camera. It’s set to record at 1080p, 30fps. Here’s a 5 second sample (11 MB).

  Videos from this phone come out at about 17 Mbps on average. I tried to compress it with ffmpeg with -c:v libx264 -crf 23 -preset veryslow, the result comes out at about 5.5 MB, which is about 9 Mbps.

  I think this bitrate is a bit too much. When I look at torrent file listings, I can see high quality videos at 3 GB in size on average, and if such a movie is 90 minutes long on average, that is about 4-5 Mbps which sounds okay.

  I’m wondering, why the big difference ? I can notice that my video is noisy/grainy (which is expected from a phone), and that might reduce compressibility. I tried a few ffmpeg filters, like hqdn3d and atadenoise, but the noise mostly remained (maybe I didn’t play with it enough). Then I figured, the video is also shaky (which is also expected), and that might reduce compressibility too (and even makes temporal noise filtering less effective). I tried to stabilize it with the deshake filter, but that didn’t help either.

  I know I could just limit the bandwidth to whatever I like, but there must be a reason why ffmpeg thinks it needs a high bandwidth to maintain a certain quality, and a lower bandwidth would just decrease the quality.

  Why do these videos have such a high bitrate ? What’s the best way to compress them more while keeping or even increasing their quality ?