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• Problem understanding audio stream number of samples when decoded with ffmpeg

  21 janvier 2021, par Michael Brown

  The two streams I am decoding are an audio stream (adts AAC, 1 channel, 44100, 8-bit, 128bps) and a video stream (H264) which are received in an Mpeg-Ts stream, but I noticed something that doesn't make sense to me when I decode the AAC audio frames and try to line up the audio/video stream timestamps. I'm decoding the PTS for each video and audio frame, however I only get a PTS in the audio stream every 7 frames.

  


  When I decode a single audio frame I get back 1024 samples, always. The frame rate is 30fps, so I see 30 frames each with 1024 samples which comes equals 30,720 samples and not the expected 44,100 samples. This is a problem when computing the timeline as the timestamps on the frames are slightly different between the audio and video streams. It's very close, but since I compute the timestamps via (1024 samples * 1,000 / 44,100 * 10,000 ticks) it's never going to line up exactly with the 30fps video.

  


  Am I doing something wrong here with decoding the ffmpeg audio frames, or misunderstanding audio samples ?
And in my particular application, these timestamps are critical as I am trying to line up LTC timestamps which are decoded at the audio frame level, and lining those up with video frames.

  


  FFProbe.exe :

  


  Video:
r_frame_rate=30/1      
avg_frame_rate=30/1    
codec_time_base=1/60
time_base=1/90000      
start_pts=7560698279   
start_time=84007.758656

Audio:
r_frame_rate=0/0
avg_frame_rate=0/0
codec_time_base=1/44100
time_base=1/90000
start_pts=7560686278
start_time=84007.625311


  


• avformat/http: increase BUFFER_SIZE to MAX_URL_SIZE + HTTP_HEADERS_SIZE

  11 mai 2020, par Joey Smith

  avformat/http: increase BUFFER_SIZE to MAX_URL_SIZE + HTTP_HEADERS_SIZE
  Some real-world sites use an authorization header with a bearer token ; when
  
  combined with lengthy request parameters to identify the video segment,
  
  it's rather trivial these days to have a request body of more than 4k bytes.
  MAX_URL_SIZE is hard-coded to 4k bytes in libavformat/internal.h, and
  
  HTTP_HEADERS_SIZE is 4k as well in libavformat/http.h, so this patch increases
  
  the buffer size to 8k, as that is the default request body limit in Apache, and
  
  most other httpds seem to support at least as much, if not more.
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavformat/http.c

• How do I increase the quality of a gif using ffmpeg from a web address [closed]

  1er août 2023, par Alteria

  I'm using command line/powershell on windows 11 along with ffmpeg to download gifs from web addresses. When I do this, though, the quality of the output is greatly decreased, even if the original file was itself a gif. Is there w way to fix this ?

  


  I'm doing this with .gif files, as well as .mp4 and .webm files using web links and addresses.

  


  The command I use is ffmpeg -i https://somewebsite.com/12345.gif "custom name.gif" when downloading gifs. The quality is always slightly decreased, and in some cases very decreased. I would like to keep this from happening. I also use the exact same command when downloading .gif's and .mp4's, with ffmpeg -i https//:somewebsite/123456.webm "custom name.gif" and ffmpeg -i https://somewebstie/123456.mp4 "custom name.gif" respectivly.

  


  What should I use instead of this in order to maintain the quality of the original .gif files and get better quality .gifs from the .webm and .mp4's ?

  


  =============

  


  Some of the other answers I have looked for have not answered what to do with links, and the other example haven't worked either.

  


  The one-liner command ffmpeg -ss 23.0 -t 1.8 -i input.mp4 -filter_complex "[0:v] split [a][b];[a] palettegen [p];[b][p] paletteuse" output_trimmed_enhanced.gif supplied at banner-bear.com did not work, instead throwing an error 
*This specific example used a .gif file for the ffmpeg -i <file></file>, but the same error occurs when using .mp4's and .webm ;s

  


  I am also aware of the tool "gifski", posed by another user when they were asked a similar question on stack overflow (the question available here FFmpeg : high quality animated GIF ?). I would prefer to not download additional software in order to do what I wanted, so is there a way to circumvent this ?

  


  Edit

  


  I have found this forum post as one of the answers of this question : How do I convert a video to GIF using ffmpeg, with reasonable quality ?. This was the fourth (4th) answer down. This solution worked ! The command itself looks like this ffmpeg -i input.mp4 -filter_complex 'fps=10,scale=320:-1:flags=lanczos,split [o1] [o2];[o1] palettegen [p]; [o2] fifo [o3];[o3] [p] paletteuse' out.gif.

  


  I, however, have absolutely no idea how this command works. While this does work, I think it's going to be hard to remember this (and other) long commands. I want to be able to remember the commands as much as possible, and also to know what each part of it does. Is there an easier or shorter way of doing this command ? Or if not, what exactly does that command above do ?

  


  *I had seen palettegen and paletteuse when searching for the answer to this question, but I had a hard time understanding and following the documentation give on FFmpeg's Filter Documentation FFmpeg Filters Documentation, as well as other stack-overflow questions on these commands. Can someone show me coherent or simplified documentation for the problem I am trying to solve.