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• Cut .mkv Video using ffmpeg without changing original bitrate

  23 janvier 2021, par benito_h

  I accidently said an unappropriate swear word during an educational video (good start I know). So I would like to remove this section from the .mkv video. However I would like the video and audio bitrate and quality unchanged.

  


  First, I tried cutting the video slightly after the relevant time stamp without reencoding it, using for example

  


  ffmpeg -i input.mkv -ss 00:01:09.200 -c copy -t 4:11 output.mkv


  


  but this way the first couple of seconds seem to get lost.

  


  Is there a way to remove the relevant segment (01:08.800 to 01:09.200) while maintaining the same bitrate / quality for audio and video ? Since only formulas are shown, a slight out-of-sync wouldnt even matter.

  


• Why Yuv data readed from ffmpeg is different from original input yuv ?

  13 mai 2021, par sianyi Huang

  I use ffmpeg to make HDR test video, my approach is write a image, converting the image to yuv420p and then use ffmpeg to make the HDR test video.

  



  But I found the yuv data readed from mp4 is different from the original input..
I was stucked in here for a while, does anyone know how to read the correct yuv data from mp4 ?

  



  #ffmpeg encode command
ffmpeg_encode_mp4 = \
"ffmpeg -y -s 100*100 -pix_fmt yuv420p -threads 4 -r 1 -stream_loop -1 -f rawvideo -i write_yuv.yuv -vf \
scale=out_h_chr_pos=0:out_v_chr_pos=0,format=yuv420p10le \
-c:v libx265 -tag:v hvc1 -t 10 -pix_fmt yuv420p10le -preset medium -x265-params \
crf=12:colorprim=bt2020:transfer=smpte2084:colormatrix=bt2020nc:master-display=\"G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(10000000,1)\":max-cll=\"1000,400\" \
-an test.mp4"

#ffmpeg read yuv from mp4 command
ffmpeg_extract_yuv = "ffmpeg -i test.mp4 -vframes 1 -c:v rawvideo -pix_fmt yuv420p read_yuv.yuv"


#make 100*100 yuv raw
w, h = 100, 100
test_gray = 255
test = np.full((100, 100, 3), test_gray, dtype=np.uint8)
yuv_cv = cv.cvtColor(test, cv.COLOR_RGB2YUV_I420)
yuv_cv.tofile("write_yuv.yuv")

#encode yuv raw to mp4 with HDR metadata
print(ffmpeg_encode_mp4)
result = subprocess.check_output(ffmpeg_encode_mp4, shell = True)
print(result)
sleep(0.5)

#extract yuv from mp4
kill_existing_file("read_yuv.yuv")
print(ffmpeg_extract_yuv)
result = subprocess.check_output(ffmpeg_extract_yuv, shell = True)
print(result)
sleep(0.5)

write_yuv = np.fromfile("write_yuv.yuv",dtype='uint8')
read_yuv = np.fromfile("read_yuv.yuv",dtype='uint8')

print("input gray:", test_gray)
print("write_yuv", write_yuv[:10])
print("read_yuv", read_yuv[:10])

reader = imageio.get_reader("test.mp4")
img = reader.get_data(0)
print("imgeio read:", img[50, 50])

'''
ouput result:
input gray: 255
write_yuv [235 235 235 235 235 235 235 235 235 235]
read_yuv [234 235 234 235 234 235 234 235 234 235]
imgeio read: [253 253 253]
'''


  



  I have no idea how to validate the video I made is corret
Any feedback will be very appreciated !

  


• FFMPEG with -vf yadif on progressive file produces incorrect 'Original Frame Rate' metadata double

  28 septembre 2020, par hedgehog90

  I've got an ffmpeg command that I often use, I incorporate the yadif argument for content that may or may not be interlaced :

  


  ffmpeg -i input.mkv -c copy -c:v hevc_nvenc -c:a:0 aac -b:a 192k -vf yadif=mode=1:deint=1 output.mkv

  


  This means if input.mkv is an interlaced video, I get double the frame rate and the footage is deinterlaced, and if it's progressive it remains so and the frame rate doesn't change, exactly as I want it.

  


  However, I've just noticed in Mediainfo that progressive videos processed by this command, it adds this mysterious "Original Frame Rate" tag (I assume it's just metadata)

  


  

  


  It doesn't appear to affect playback in VLC or MPV, however it is recognized in MPV as 'framerate (Specified)'...

  


  How do I prevent ffmpeg from generating this tag when using the yadif filter ?