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• Learn Multimedia Programming By Writing A JPEG Decoder

  6 janvier 2011, par Multimedia Mike — Programming

  For those of you who hack on multimedia tech, how did you get started ? Did you begin by studying the mathematical underpinnings of multimedia codec algorithms ? Or did you find a practical problem and jump right in by writing code ? (Personally, I was always more of a nuts & bolts hacker than a math guy.) I ask because I occasionally get emails from aspiring multimedia hackers who want to know where to begin. Invariably, they want to go the math-first route. I heavily discourage this approach.

  I have a crazy idea for anyone who wants a crash course on multimedia hacking : write a JPEG decoder. In doing so, you will be exposed to a lot of key domain concepts such as bitstream parsing, Huffman decoding, dequantization, zigzagging, the dreaded (inverse) discrete cosine transform, YUV vs. RGB colorspaces, macroblock organization, delta coding, and run length coding.

  Sure, JPEG decoding is a solved problem. But that’s hardly the point. Why would you enter an unfamiliar field and hope to come up to speed on the basics by leaping straight into the domain’s unsolved problems ? If you are successful in this exercise, no one will ever use the fruits of your labor, but that doesn’t really matter.

  So, do you want to learn multimedia hacking quickly ? Then grab a JPEG file (maybe create a few contrived ones that are small, have friendly dimensions, and feature predictable patterns), grab a good JPEG reference, and implement the decoding algorithm in the language and platform of your choice.

  On the matter of the reference, my personal favorite reference has always been A note about the JPEG decoding algorithm by Cristi Cuturicu. The English grammar is a bit dodgy but overall, it might be the best reference you’ll find on the matter— as simple as it needs to be, but no simpler.

  Good luck !

• Mirrored Arabic Letters using TextClip Moviepy

  4 août 2020, par Sam

  I am trying to render the video which contains arabic letters. let's use مرحبا for the example. After video rendered the result is mirrored.

  


  background = mp.ColorClip(mobile_size, (255, 255, 255), duration=0.5) #float(audiolength.info.length)
text1 = mp.TextClip(english, fontsize=45, color=fcolor, font=Font, size= (mobile_size[0], 185), method = 'caption', align="south").set_duration(0.5) #float(audiolength.info.length)
text2 = mp.TextClip(formatChineseSentences(translated).encode("utf-8"), fontsize=45, color=fcolor2, font=Font, size= (mobile_size[0], 185), method = 'caption', align="north").set_duration(0.5) #float(audiolength.info.length)

clip1 = mp.CompositeVideoClip([background, text1.set_position(('center', "top")), text2.set_position(('center', "bottom"))])


  


  Expected Behavior

  


  

  


  Actual Behavior

  


  

  


  Steps to Reproduce the Problem

  


  Rendering TextClip with Arabic Characters. For this case we can use مرحبا.

  


  Specifications

  


  Python Version : Python 3.8.5
Moviepy Version : 1.0.3
Platform Name : Mac OS Catalina
Platform Version : 10.15.6

  


• How to fix call lib ffmpeg by c#

  20 février 2017, par Thang Tran

  string _a= -i "D:_InputFolder\Jamaican man talking the truth about #zika virus.mp4" -filter_complex "[0:a]atempo=0.9,volume=1.6,asetrate=r=44100*33.6/30,atempo=30/33.6,highpass=f=400,lowpass=f=4100,earwax,biquad,compensationdelay,equalizer=f=222:width_type=o:width=2:g=5,equalizer=f=444:width_type=h:width=220:g=5 ; setpts=PTS/0.9" -vcodec libx264 -pix_fmt yuv420p -r 30 -g 60 -b:v 1400k -profile:v main -level 3.1 -acodec libmp3lame -b:a 128k -ar 44100 -metadata title="" -metadata artist="" -metadata album_artist="" -metadata album="" -metadata date="" -metadata track="" -metadata genre="" -metadata publisher="" -metadata encoded_by="" -metadata copyright="" -metadata composer="" -metadata performer="" -metadata TIT1="" -metadata TIT3="" -metadata disc="" -metadata TKEY="" -metadata TBPM="" -metadata language="eng" -metadata encoder="" -threads 0 -preset superfast "D:_OutputFolder\videoOutput.mp4"

  -----------this is the code goi goi sua sound in c # error

  string _b= -i "D:_InputFolder\Jamaican man talking the truth about #zika virus.mp4" -acodec pcm_u8 -ar 22050 "D:_OutputFolder\videoOutput.wav"
  — with code editing video style is back.

  file class run ffmpeg
  call c# :
  string _result = ffmpeg.RunCommand(_b) ;//wordless

  string _result2 = ffmpeg.RunCommand(_a) ;//error

  file class call ffmpeg :

  -file project demo error :
  https://drive.google.com/open?id=0B9dxSeLrFswjVmNGd1IzcUpncE0

  thank you and sorry if my english is the poor