<p>I was able to produce the same size as Youtube by varying the <code>qp</code> option for x264. The value that worked to approximately the same size was qp=20.</p>

CC BY-SA 4.0
2023-01-24T16:44:02.107Z
2023-01-24T16:44:02.107Z
er0
<p>I am unable to re-encode an H.264 video that I downloaded from Youtube back to its original size. The MediaInfo is pasted below. The size of the video stream is 20 MB.</p>
<p>I decoded the video into raw YUV (using ffmpeg and JM separately, ensuring that I get an identical file). Then I re-encoded it using the x264 library with a variety of configs. The encoded H.264 videos that I generated are around 40 MB in size.</p>
<p>This is the commandline that I used:
<code>x264 -o out.h264 --input-res 1280x720 --preset slow autl.yuv</code></p>
<p>Any ideas on what options I might be missing that YouTube would have used to encode the video?</p>
<p>Mediainfo:</p>
<pre><code>General
Complete name                            : autl.h264
Format                                   : AVC
Format/Info                              : Advanced Video Codec
File size                                : 19.9 MiB
Writing library                          : x264 core 155 r2901 7d0ff22

Video
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Main@L3.1
Format settings                          : CABAC / 3 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 3 frames
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Variable
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Writing library                          : x264 core 155 r2901 7d0ff22
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709
</code></pre>

<encoding><youtube><h.264><libx264><x264>
Encoding to the same H.264 size as YouTube
er0
# Encoding to the same H.264 size as YouTube

(Asked by: username_0 on 2023-01-23)

I am unable to re-encode an H.264 video that I downloaded from Youtube back to its original size. The MediaInfo is pasted below. The size of the video stream is 20 MB.
I decoded the video into raw YUV (using ffmpeg and JM separately, ensuring that I get an identical file). Then I re-encoded it using the x264 library with a variety of configs. The encoded H.264 videos that I generated are around 40 MB in size.
This is the commandline that I used:
x264 -o out.h264 --input-res 1280x720 --preset slow autl.yuv
Any ideas on what options I might be missing that YouTube would have used to encode the video?
Mediainfo:
General
Complete name                            : autl.h264
Format                                   : AVC
Format/Info                              : Advanced Video Codec
File size                                : 19.9 MiB
Writing library                          : x264 core 155 r2901 7d0ff22

Video
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Main@L3.1
Format settings                          : CABAC / 3 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 3 frames
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Variable
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Writing library                          : x264 core 155 r2901 7d0ff22
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709

**Tags:** encoding, youtube, h.264, libx264, x264


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## 1 answers

### Answer by username_0 on 2023-01-24. Score: 1 | Accepted answer

I was able to produce the same size as Youtube by varying the `qp` option for x264. The value that worked to approximately the same size was qp=20.


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