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• FFmpeg 5 C api codec end of stream situation

  11 mars 2023, par Guanyuming He

  I'm new to FFmpeg api programming (I'm using version 5.1) and am learning from the documentation and official examples.

  


  In the documentation page about send/receive encoding and decoding API overview, end of stream situation is discussed briefly :

  


  


  End of stream situations. These require "flushing" (aka draining) the codec, as the codec might buffer multiple frames or packets internally for performance or out of necessity (consider B-frames). This is handled as follows :

  


  


  


  Instead of valid input, send NULL to the avcodec_send_packet() (decoding) or avcodec_send_frame() (encoding) functions. This will enter draining mode.
Call avcodec_receive_frame() (decoding)
or avcodec_receive_packet() (encoding) in a loop until AVERROR_EOF is returned. The functions will not return AVERROR(EAGAIN), unless you forgot to enter draining mode.
Before decoding can be resumed again, the codec has to be reset with avcodec_flush_buffers().

  


  


  As I understand it, when I get AVERROR_EOF, I have reached a special point where I need to drain buffered data from the codec and finally reset the codec with avcodec_flush_buffers(). Without doing it, I cannot continue decoding/encoding.

  


  Then I have some questions :

  


  

  1. If I received EOF when I already finished sending data (e.g. when after EOF is returned by av_read_frame()), how should I tell if it's really finished ?

  


  2. The data returned from the receive_... functions during draining, should I take them as valid ?

  


  


  I might have found answers to those in the official examples, but I'm not sure if the answer is universally true. I noticed that in some official examples, like in transcode_aac.c, draining is only done for the first EOF reached, and then after the second one is received, it is regarded that there are really nothing left. Any data received during draining is also written to the final output.

  


  I just wonder, Is it true for all multimedia files in ffmpeg ?

  


  I appreciate your response and time in advance. :)

  


• How should one start with ffmpeg's API ?

  20 mai 2018, par JoeDough

  I’d like to make a real time streaming program that takes input from a webcamera, ffmpeg looks like a good library for encoding a stream of images but there is no documentation or community tutorials (there is just a doxygen API reference).Where should I start if there’s no official documentation ?

• How to generate the first few HLS playlist files for a live broadasting event ?

  1er mars 2014, par user3367166

  Knowing that HLS is based on a playlist of N segment files, how to properly generate the first (N-1) playlist files for a live broadcasting event (sliding window method) ?
   should we wait for the first N segments to be recorded, and send a complete first playlist file ? This of course works but means that there is a delay of N x segment_duration before streaming starts.
   or is there an official way of sending "partial" playlist files such that streaming starts after 1 x segment_duration ?

  I have experimented with partial playlist files : ffmpeg 2.1.3 appends new segments into the playlist as they are recorded (below). I find this a reasonable way but my ipod5 usually stops playback after the first playlist or sometimes manages to playback the first few playlists but with much choppiness, so I believe it is not a supported way. Is there any official solution ?

  1. 1st playlist file :

     #EXTM3U
     
     #EXT-X-VERSION:3
     
     #EXT-X-TARGETDURATION:8
     
     #EXT-X-MEDIA-SEQUENCE:0
     
     #EXTINF:8,
     
     segment0.ts

  2. 2nd playlist file :

     #EXTM3U
     
     #EXT-X-VERSION:3
     
     #EXT-X-TARGETDURATION:8
     
     #EXT-X-MEDIA-SEQUENCE:0
     
     #EXTINF:8,
     
     segment0.ts
     
     #EXTINF:1,
     
     segment1.ts

  3. 3rd playlist file :

     #EXTM3U
     
     #EXT-X-VERSION:3
     
     #EXT-X-TARGETDURATION:8
     
     #EXT-X-MEDIA-SEQUENCE:0
     
     #EXTINF:8,
     
     segment0.ts
     
     #EXTINF:1,
     
     segment1.ts
     
     #EXTINF:8,
     
     segment2.ts