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• How to run a video on chromium/lubuntu smoothly on a low-end machine ?

  29 juillet 2020, par Altuğ Ceylan

  the cpu of the machine is Atom X5-Z8350 with a ram size of 4 GB. It does not have an external gpu.
The problem is that when it runs a video on chromium such as a youtube video, it stutters and fps drop happens. I found out that the cpu supports h264 and vp8, and chromium only supports vp-8 and vp-9. Therefore, I used ffmpeg to transcode a video I downloaded from youtube to see if it was going to help.
I used the following script from my github repository which also contains driver update scripts etc

  


  
#$1 input filename
#$2 good realtime best
#$3 --cpu-used for best and good deadline valid values are from 0 to 5 for realtime 0 to 15
#$4 tile columns allow multi threading use powers of 2 eg 2=4
#$5 no threads to use
#$6 minrate around 2k is good for 1080p60
#$7 out filename
# -b:v bitrate 512k maybe too low for 720p30 try 1500k to 2000k 
#for fast/quality use realtime 6-7 
#for very good quality use good 2
start=$(date +%s.%N)
ffmpeg -i $1 -r 30 -g 90 -s 1280x720 -aspect 16:9 -c:v libvpx -deadline $2 -row-mt 1 -b:v 2500k -threads $5 -tile-columns $4 -cpu-used $3 -minrate $6 -bufsize 3000k -maxrate 3000k -crf 30 -frame-parallel 1 $7.webm
duration=$(echo "$(date +%s.%N) - $start" | bc)
execution_time=`printf "%.2f seconds" $duration`
echo "Script Execution Time: $execution_time"



  


  I changed crf to 5, -r to 120 -s to 1920x1080 and passed $2 as realtime, $3 as 7, $4 as 2 , $5 as 4, $6 as 2000k, I used the following video https://www.youtube.com/watch?v=jZKvJY6gDfg. It was a lot better than before, the chromium was having hard time running 720p30 but now it actually ran the 1080p120 video with minor tear and fps drops. How can I prevent the tears and the fps drops from happening ?

  


• How to trim and concatenate mp4 files with subtitles ?

  16 juin 2018, par Tommi Komulainen

  I’ve two mp4 files with subtitles that I want to concatenate while trimming a little from end and beginning. I’ve read the FAQ and have come up with following ffconcat input :

  ffconcat version 1.0
  
  
  
  file '1.mp4'
  
  inpoint 0:34:20
  
  outpoint 0:34:22
  
  
  
  file '2.mp4'
  
  inpoint 0:00:11
  
  outpoint 0:00:12

  Running ffmpeg -i in.txt -c copy -c:s copy -y out.mp4 generates a file containing only the bits from the first file and then aborts with error

  [mp4 @ 0x7fda8d80d000] Application provided invalid, non monotonically increasing dts to muxer in stream 2: 276960 >= -169518
  
  av_interleaved_write_frame(): Invalid argument

  Leaving out -c:s copy joins the video and audio alright but leaves out subtitles. In this case instead of fatal error as above there are merely (repeated) warnings about

  [mp4 @ 0x7fd13300b000] Non-monotonous DTS in output stream 0:1; previous: 437248, current: 423638; changing to 437249. This may result in incorrect timestamps in the output file.

  I tried using the concat filter instead though I don’t see the reason. Best I’ve come up with forgets the subtitles from the second file.

  What’s causing the error about "non monotonically increasing dts" and how can I fix/avoid it ?

  ffmpeg version 4.0

• FFmpeg(C/libav) VPX to mpeg2video stream cannot be reproduce in VLC

  21 septembre 2017, par caiomcg

  I am currently trying to transcode a VPX(VP8/VP9) video to a mpeg2video and stream it over UDP with mpegts.

  I have initialized all of the contexts and the streams and as long as I stream it to ffplay it works, if I send the stream to VLC or another player, the receiver only display the first frame and do nothing else. If I do the same thing through the command line it works flawlessly - ffmpeg -re -i video.webm -an -f mpegts udp://127.0.0.1:8080

  My output context :

  this->output_codec_ctx_->codec_type    = AVMEDIA_TYPE_VIDEO; // Set media type
  
  this->output_codec_ctx_->pix_fmt       = AV_PIX_FMT_YUV420P; // Set stream pixel format
  
  this->output_codec_ctx_->time_base.den = ceil(av_q2d(input_stream->r_frame_rate));     // Add the real video framerate. Eg.: 29.9
  
  this->output_codec_ctx_->time_base.num = 1;                  // Numerator of the framerate. Eg.: num/29.9
  
  this->output_codec_ctx_->width         = input_stream->codecpar->width;  // Video width
  
  this->output_codec_ctx_->height        = input_stream->codecpar->height; // Video height
  
  this->output_codec_ctx_->bit_rate      = 400000; // Video quality
  
  this->output_codec_ctx_->gop_size      = 12;
  
  this->output_codec_ctx_->max_b_frames  = 2;
  
  this->output_codec_ctx_->framerate     = this->input_codec_ctx_->framerate;
  
  this->output_codec_ctx_->sample_aspect_ratio     = this->input_codec_ctx_->sample_aspect_ratio;

  My av_dump :

  Output #0, mpegts, to 'udp://127.0.0.1:20010':
  
    Metadata:
  
      encoder         : Lavf57.72.101
  
      Stream #0:0: Video: mpeg2video (Main), 1 reference frame, yuv420p, 480x640 (0x0), q=2-31, 400 kb/s, SAR 1:1 DAR 3:4, 24 fps, 24 tbr, 90k tbn

  FFMPEG av_dump :

  Output #0, mpegts, to 'udp://127.0.0.1:20010':
  
    Metadata:
  
      title           : Tears of Steel
  
      encoder         : Lavf57.72.101
  
      Stream #0:0: Video: mpeg2video (Main), yuv420p, 480x640 [SAR 1:1 DAR 3:4], q=2-31, 200 kb/s, 24 fps, 90k tbn, 24 tbc (default)
  
      Metadata:
  
        encoder         : Lavc57.96.101 mpeg2video
  
      Side data:
  
        cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1

  Any ideia on what I may be doing wrong ?