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• How to set AVCodecContext args with h264 correctly ?

  15 juin 2017, par wzjing

   I’m doing a video transcoder demo with ffmpeg lib and libx264 lib. I already can transcode video successully, but the output video can only play by some powerful player like VLC. I need it can be played by the Win10 default player and the Android default player. I hava found the reason may be encode AVCodecContext args. I try to copy those args frome decode AVCodecContext, the output can be played by Win10 defualt player, but the video became totally black.
   Here is my encode AVCodecContext args :

          encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
  
  
          if (!encoder) {
  
              av_log(NULL, AV_LOG_FATAL, "Necessary encoder not found\n");
  
              return AVERROR_INVALIDDATA;
  
          }
  
          enc_ctx = avcodec_alloc_context3(encoder);
  
          enc_ctx->height = output_height;
  
          enc_ctx->width = output_width;
  
          enc_ctx->sample_aspect_ratio = dec_ctx->sample_aspect_ratio;
  
          enc_ctx->bit_rate = 1000000;
  
  
  
          /* take first format from list of supported formats */
  
          if (encoder->pix_fmts)
  
              enc_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
  
          else
  
              enc_ctx->pix_fmt = dec_ctx->pix_fmt;
  
  
  
          enc_ctx->time_base = av_inv_q(dec_ctx->framerate);
  
          enc_ctx->gop_size = 12;
  
          av_opt_set(enc_ctx->priv_data, "preset", "slow", 0);
  
          av_opt_set(enc_ctx->priv_data, "tune", "zerolatency", 0);
  
  
  
          enc_ctx->profile = FF_PROFILE_H264_HIGH;
  
          enc_ctx->codec_type = AVMEDIA_TYPE_VIDEO;       
  
  
  
          enc_ctx->codec_tag = 0;

• Add a text/caption to the first few seconds of a cut video ?

  6 mai 2022, par JR Jr.

  I want to cut a video and at the same time add a caption during the first few seconds of the video using drawtext. I have tried lots of different google searches but all turned out to be totally unhelpful for this specific purpose (even the answers on the SS pages). Also, I am on Windows, I don't care for other OS's, such as Unix/ubuntu/Mac.

  


  Let's use the below cut syntax as an example. It's cutting and changing the format from mkv to mp4, and I want to add a simple title to be displayed in the first 5 seconds of the video, since this will be done to various files and then they will be concatenated together and it's good to let the viewer know which movie each excerpt belongs to (without doing that manually for each single video, the goal is to add these texts to each of the below commands).

  


  "C:\ffmpeg\bin\ffmpeg.exe" -y -i "D:\S01\SATC - S01E03 - Bay of Married Pigs.mkv" -ss 00:18:05 -to 00:19:15 -codec copy "002-SATC - S01E03 - Bay of Married Pigs-00_18_05-00_19_15.mp4"


  


  Let's say I want to add the title "S01E03 - Bay of Married Pigs" in the center of the screen, in white, with font size 12, displayed between 1 and 5 seconds. How do I do that ?

  


  And more importantly, since these syntaxes tend to make the command line insanely long and it needs to be a one liner, is there a smarter way to feed the settings/configuration of the drawtext clause into the command line, as to not make the code very messy, long and chaotic ?
Besides, do white spaces matter/would misplaced blank spaces make the command line crash ?

  


  Been trying this for hours now, so I really appreciate your help on this.

  


• Better vertical stabilization when simultaneously cropping to widescreen format

  21 juillet 2016, par Kelley van Evert

  First of all : forgive me for maybe asking a stupid or somewhat uninformed question. I’m totally new to post processing video, stabilization, etc..

  I’m shooting 1920x1080 compressed movie files with my Canon 5D2, and afterwards crop then to cinematic 1920x800 (2.4:1). (With Magic Lantern I use an overlay bitmap when shooting. And yes, I know that with magic lantern I can shoot RAW, but my cards as well as computer are not fast enough to deal with that much data.)

  Before doing any production, I convert the big .MOV files to smaller ones, simultaneously stabilizing the video a bit, and cropping it to 1920x800. I do this with ffmpeg roughly as follows :

  ffmpeg -i f.MOV -vf vidstabdetect -f null -
  
  ffmpeg -i f.MOV -c:v libx264 -profile:v high -crf 18 -vf "vidstabtransform, crop=in_w:in_h-280" -c:a aac -strict experimental f2.mp4

  However, the fact that a great deal of the vertical resolution is being cropped is not being used to be able to handle the stabilizing transforms better. Often, the image is stretched/skewed vertically, when this is not really needed given the crop used.

  Is it possible in any way to use the crop befenificially in the stabilizing transforms ?

  An example is the frame below. Here, I would rather have that the image is not stretched vertically at all, and just get away with a slight static zoom (crop), because the horizontal black border is the only problem in this frame.