Recherche avancée

Sur d’autres sites (9675)

• avformat_write_header() changes my stream's time_base

  12 avril 2023, par greken

  I have a high framerate camera which can capture >2000 fps. My plan was to assign actual capture timestamps with µs resolution to the frames and encode with H.264 in a matroska file.

  


  So I set the time_base of both the AVStream and the AVCodecContext to {1, 1'000'000}. But after calling avformat_write_header(avFormatContext, nullptr) I notice that the stream's time_base is {1, 1'000}. Now, since my framerate is double this resolution, I get identical consecutive timestamps and half my frames get lost when I extract them from the video file.

  


  Does anyone have an idea why this is happening and what I can do about it ? Preferably in a way that preserves the correct timestamps.

  


• Make blurred background faster with ffmpeg

  26 septembre 2022, par Peter Czask

  I have a vertical videos which I'll like to make them horizontal 1920x1080 with blurred background.

  


  I do it with this command :

  


  ffmpeg -i input.mp4 -vf 'split[original][copy];[copy]scale=ih*16/9:-1,crop=h=iw*9/16,gblur=sigma=20[blurred];[blurred][original]overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2'  output.mp4 


  


  which that code I'm satisfied with the result, except that it takes very very long time to produce it. Is there any way to speed it up ? I noticed that the blurred part on the background uses half of the overlay video (non blurred), I'll like to blurry just with the edge (or 10 pixels) of the non blurred video (if this makes the encoding faster)...

  


• How to process a video to mp4 with ffmpeg for quality and compatibility ?

  30 mai 2024, par Luis A. Florit

  I am beginning to be more serious about video. I am processing my videos with ffmpeg in a fully updated Linux into mp4 to use it in HTML5 directly.

  


  Now, I have old AVI videos that I want to convert to mp4 with ffmpeg for use with HTML5. In particular, I have this one :

  


  http://luis.impa.br/photo/1101_aves_ce/caneleiro-de-chapeu-preto_femea_Quixada-CE-110126-E_05662+7a.avi

  


  (I know, terrible quality... sorry). According to ffprobe :

  


  Duration: 00:01:35.30, start: 0.000000, bitrate: 1284 kb/s
Stream #0:0: Video: mpeg4 (Simple Profile) (DX50 / 0x30355844), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 1144 kb/s, 30 fps, 30 tbr, 30 tbn, 30 tbc
Stream #0:1: Audio: mp3 (U[0][0][0] / 0x0055), 44100 Hz, stereo, s16p, 128 kb/s


  


  That seems perfect : mpeg4 video and mp3 audio. So I tried :

  


  ffmpeg -i input.avi -acodec copy -vcodec copy output.mp4


  


  It generates a file that plays nicely in mplayer, but not in firefox getting an error :

  


  Video format or MIME type not supported.


  


  Chrome plays the audio, but no video is shown... Now, if I do :

  


  ffmpeg -i input.avi output.mp4


  


  firefox works, but the video is reencoded in another one with half the size (half the bitrate). This is what ffprobe says about the reencoded video :

  


  major_brand     : isom
minor_version   : 512
compatible_brands: isomiso2avc1mp41
encoder         : Lavf57.71.100
Duration: 00:01:35.30, start: 0.000000, bitrate: 685 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x480 [SAR 1:1 DAR 4:3], 548 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)


  


  I suppose that I am loosing lots of quality (and time processing the video). So, my questions :

  


  


  1. Why are browsers not playing my video with the copy codecs ?

     


  


  2. Can I work with ffmpeg in this particular file without reencoding ? If yes, how ?

     


  


  3. If I need to reencode, which are "reasonable" parameters to keep close to the original quality ? Would something like

     


     ffmpeg -i input.avi -b:v 1024k -bufsize 1024k output.mp4

     


  


  


  suffice for this video ? This generates a new video with size closer to the original one.

  


  Thanks !