[SOLVED] [ffmpeg] How to compress MP4 file further?

[yetanotherlogin]

Hello

I have a 2hrs video file of a conference that is currently about 700MB:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'input.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf57.34.103
  Duration: 02:08:37.48, start: 0.000000, bitrate: 810 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x512 [SAR 64:45 DAR 16:9], 674 kb/s, 25 fps, 25 tbr, 12800 tbn (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 129 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

If possible, I'd like to cut it in size by half without recompressing the audio stream. I tried this, but it barely works:

ffmpeg -i input.mp4 -b:v 100k -r 20 -c:v libx264 -vf scale=640:-1 -pix_fmt yuv420p -c:a copy -threads 2 -crf 20 -f mp4 output.mp4

Is there a more aggressive solution to get down to eg. 350MB? It's just a conference, so video doesn't matter that much, while audio is important.

Thank you.

[poisondeathray]

You have both -b:v 100k and -crf 20. They are mutually exclusive rate control methods. Erase the -crf 20.

100kbps should give you about 1/4 the size of the original if it's met, because you had 674kbps video, 129kbps audio in the source - If those were correctly listed by ffmpeg . So you probably want to shoot for higher.

[pandy]

Prefilter video quite aggressively with https://ffmpeg.org/ffmpeg-filters.html#toc-hqdn3d-1 perhaps you may consider, reducing audio bitrate give you less than 50MB gain (IMHO no sense to go bellow 88 - 96kbps unless lowpass filter around 9 - 10kHz applied which seem to be perfectly fine for conference, you may improve perceived legibility of audio by applying some dynamics compression together with bandpass filter 150Hz - 9kHz ).
Don't change framerate (-r 20 is wrong - it may even reduce video compressibility). You may consider to apply temporal blur trough

tblend=all_mode=average

.
Adjust/set crf to somewhere around 26 - 28.

[yetanotherlogin]

Thanks much for the infos.

[Baldrick]

medialover: Please remove your signature. Spamming/Advertising is not allowed. See https://forum.videohelp.com/threads/72386-Forum-rules-Acceptable-Use-Policy-(AUP)? . Especially for CRAP like PAVTUBE!!!

edit: banned.