55

I have some 4K 3840x2160 footage in MP4 format that I need to bring down to 1080p. I tried running 

ffmpeg -i orig.mp4 -vf scale=1920:1080 smaller.mp4

but the result is very poor quality, with the entire image being composed of square "tiles" as if I was magnifying 4:1.

Here is the output of running this command:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'origs/P1000003.MP4':
  Metadata:
    major_brand     : mp42
    minor_version   : 1
    compatible_brands: mp42avc1
    creation_time   : 2015-02-19 17:10:38
  Duration: 00:05:14.48, start: 0.000000, bitrate: 95903 kb/s
    Stream #0.0(und): Video: h264 (High), yuvj420p, 3840x2160 [PAR 1:1 DAR 16:9], 95792 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
    Metadata:
      creation_time   : 2015-02-19 17:10:38
    Stream #0.1(und): Audio: aac, 48000 Hz, stereo, s16, 125 kb/s
    Metadata:
      creation_time   : 2015-02-19 17:10:38
Incompatible pixel format 'yuvj420p' for codec 'mpeg4', auto-selecting format 'yuv420p'
[buffer @ 0x22a3420] w:3840 h:2160 pixfmt:yuvj420p
[scale @ 0x22a3ce0] w:3840 h:2160 fmt:yuvj420p -> w:1920 h:1080 fmt:yuv420p flags:0x4
Output #0, mp4, to '1-short.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 1
    compatible_brands: mp42avc1
    creation_time   : 2015-02-19 17:10:38
    encoder         : Lavf53.21.1
    Stream #0.0(und): Video: mpeg4, yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 25 tbn, 25 tbc
    Metadata:
      creation_time   : 2015-02-19 17:10:38
    Stream #0.1(und): Audio: libvo_aacenc, 48000 Hz, stereo, s16, 200 kb/s
    Metadata:
      creation_time   : 2015-02-19 17:10:38
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press ctrl-c to stop encoding
frame=  125 fps=  6 q=31.0 Lsize=     968kB time=5.00 bitrate=1586.7kbits/s    
video:842kB audio:123kB global headers:0kB muxing overhead 0.421047%

I know from experience that ffmpeg is an excellent tool, so I must be screwing up the options/parameters somehow...

How can I do this?

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8
  • Please show the full, complete console output from your command. You can just encode a short segment, so add -t 10 to make a 10 second output. Why do you want to downscale? What is the use case for your scaled output? This info will help me provide a more accurate answer.
    – llogan
    Commented Feb 19, 2015 at 20:22
  • @LordNeckbeard I have just added the console output. I want to downscale so that I can more easily share these clips with people who are working with me.
    – lara michaels
    Commented Feb 20, 2015 at 0:10
  • 1
    Don't forget -c:a copy, since you don't want or need to re-encode the audio stream. Use -map 0 to copy any chapter metadata, or other stuff. (ffmpeg only takes 1 vid + 1 aud by default.)
    – Peter Cordes
    Commented Feb 23, 2015 at 3:10
  • 1
    Also, -sws_flags lanczos+print_info will use a better scaling algo than the default (bilinear I think). stlb's answer covers the video encoding part of the process.
    – Peter Cordes
    Commented Feb 23, 2015 at 3:14
  • 2
    @PeterCordes Alternatively, scale=1920:-2:flags=lanczos. I was also going to mention the -2 for scale in my non-existent answer. For those who don't know you can put -2 in width or height, and it will automatically provide the correct value while preserving aspect ratio and making the value divisible by 2 (required by libx264 for yuv420p outputs).
    – llogan
    Commented Feb 23, 2015 at 18:04

3 Answers 3

Reset to default
41

The default settings for ffmpeg are very low quality, and since you don't specify any codec or quality parameters it's just using the defaults (I don't know why the devs don't fix that because it generates a lot of questions on forums everywhere).

Edit: the defaults are now quite sane. With a recent (as in later than 2017) build of ffmpeg you don't need to specify anything more than input and output files to achieve good useable results. You can, of course tweak to your heart's desire.

Try adding -c:v libx264 -crf 20 -preset slow to the command.

  • -c:v libx264 tells it to use the libx264 encoder, this is the default now, no need to specify it
  • crf 20 uses the Constant Rate Factor quantiser (which paradoxially means variable bit rate, but constant quality) with a value of 20 (pretty good quality; lower is better quality / larger files, higher is crappier / smaller)—default is 23,
  • the slow preset is a shortcut for a bunch of encoder settings that means it puts a bit more effort into it than the default (medium). Note that the speed presets don't change the quality of the encoded file, just the efficiency, meaning a slower encode will result in a smaller file of the same quality and a faster encode will mean a larger file of the same quality.

You can tweak these settings, see the h.264 encoding guide for instructions on what knobs to twiddle.

And if you're using the audio as-is, add c:a copy. That will do a straight copy of the audio stream without re-encoding.

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10
  • The defaults depends on the encoder. libx264 is usually used for MP4 output by default, and it produces a nice quality output with no additional options, but the ffmpeg build in the question appears to not support this encoder and therefore uses the ancient encoder mpeg4 producing MPEG-4 Part 2 video, and the defaults for it were more sane during its heyday (such as for 320x240, etc).
    – llogan
    Commented Feb 21, 2015 at 6:24
  • It's good to hear that libx264 is the default now.
    – stib
    Commented Feb 23, 2015 at 1:00
  • 1
    I'd say crf 20 is pretty darn good. 18 is functionally lossless. I do most of my videos at 23.
    – user3643
    Commented Sep 15, 2017 at 12:36
  • Most of my work gets displayed on playback devices working locally from an SD card. I don't need to optimise much for size, so I leave the quality as high as I can. I agree, I'd dial it down if I was delivering over the web.
    – stib
    Commented Sep 16, 2017 at 13:47
  • 1
    @stib I'm not asking a question. I'm saying that this is not a definite answer the problem posed (or one of the same nature). That is useful to others in the same position.
    – rewolf
    Commented Oct 25, 2017 at 6:09
19

Convert 4k to 1080 (no change in codec)

ffmpeg -i input4kvid.mp4 -vf scale=1920:1080 -c:a copy output1080vid.mp4

Convert h.264 to h.265 (no change in resolution)

ffmpeg -i input.mp4 -c:v libx265 -vtag hvc1 -c:a copy output.mp4

Convert 4k(h.264) to 1080(h.265)

  • Downscaling + Change in compression codec
ffmpeg -i input.mp4 -c:v libx265 -vtag hvc1 -vf scale=1920:1080 -crf 20 -c:a copy output.mp4

Options Explained

-i input file name or file path

-c:v libx265 -vtag hvc1 selecting compression. Default is libx264

-vf scale=1920:1080 specifying output resolution

-c:a copy copy audio as it is without any compression

-preset slow ask compression algorithm to take more time & look for more areas for compression. Default is medium. Other options are faster, fast, medium, slow, slower

-crf 20 Compression quality

-crf 0 high-quality, low compression, large file

-crf 23 default

-crf 51 low-quality, high compression, small file

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0
1

Use avconv if you want:

avconv -i 4kfile.mp4 -s hd1080 -c:v libx264 -c:a copy fullhdfile.mp4
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