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• VLC syntax to transcode and stream to stdout ?

  19 novembre 2016, par Will Tower

  Goal : I am trying to use VLC as a local server to expand the video capabilities of an app created with Adobe AIR, Flex and Actionscript. I am using VLC to stream to stdoutand reading that output from within my app.

  VLC Streaming capabilities
  VLC Flash Video
  Stream VLC to Website with asf and Flash

  Status : I am able to launch VLC as a background process and control it through its remote control interface (more detail). I can load, transcode and stream a local video file. The example app below is a barebones testbed demonstrating this.

  Issue : I am getting data in to my app but it is not rendering as video. I don’t know if it is a problem with my VLC commands or with writing to/reading from stdout. This technique of reading from stdout in AIR works (with ffmpeg for example).

  One of the various transcoding commands I have tried :

  -I rc  // remote control interface  
  
  -vvv   // verbose debuging  
  
  --sout  // transcode, stream to stdout 
  
  "#transcode{vcodec=FLV1}:std{access=file,mux=ffmpeg{mux=flv},dst=-}"

  This results in data coming into to my app but for some reason it is not rendering as video when using appendBytes with the NetStream instance.

  If instead I write the data to an .flv file, a valid file is created – so the broken part seems to be writing it to stdout. One thing I have noticed : I am not getting metadata through the stdout`method. If I play the file created with the command below, I do see metadata.

  // writing to a file
  
  var output:File = File.desktopDirectory.resolvePath("stream.flv");
  
  var outputPath:String = output.nativePath;
  
  "#transcode{vcodec=FLV1}:std{access=file,mux=ffmpeg{mux=flv},dst=" + outputPath + "}");

  ---

  Hoping someone sees where I am going wrong here.

  ---

  Update 1 : Just to add some more detail (!) – I took a look at the .flv file that is generated to examine the metadata. It appears at the head of the file as shown below. I have the correct onMetaData handler set up and see a trace of this data if I play the file from disk. I do not see this trace when reading from stdout and NetStream is in Data Generation mode. Is it possible that it isn’t getting sent to stdout for some reason ? I’ve tried generating my own header and appending that before the stream starts – I may not have the header format correct.

  

  ---

  Update 2 : So in my AIR app I was able to crudely parse the incoming stdout stream coming from VLC. I wanted to see if the FLV header data was being sent – and it appears that it is. I don’t know if it is in the correct format, etc. but as I mention above, if I write to an .flv file instead of stdout, a valid .flv file is created.

  Completely at a loss now – have tried everything I could think of and followed up every web link I could find on the issues involved. Alas – so close and it would have been so cool to leverage VLC from within AIR.

• Setting a framerate of a video created from images with ffmpeg (slowing down)

  9 octobre 2016, par jeet

  I’m making a video using ffmpeg & multiple images with this command :

  ffmpeg -f image2 -i img%d.png v.mpg

  The video is made, but plays very fast. Can I slow it down a bit ? (double duration nearly)
  If possible set the speed while creation itself please.

  I also need to add an audio "a.wav" to the video being made, possibly in the same command. Is that possible ?

  Please give me the commands
  Thanks

  When I use this command, below is the error I get :

  ffmpeg -r 12 -i pic\s%d.png -i rmt.wav -shortest -r 25 v.mpg
  
  
  
  
  
  
  
  FFmpeg version SVN-r16573, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  
  configuration: --extra-cflags=-fno-common --enable-memalign-hack --enable-pthreads --enable-libmp3lame --enable-libxvid --enable-libvorbis --enable-libtheora --enable-libspeex --enable-libfaac --enable-libgsm --enable-libx264 --enable-libschroedinger --enable-avisynth --enable-swscale --enable-gpl
  
  libavutil     49.12. 0 / 49.12. 0
  
  libavcodec    52.10. 0 / 52.10. 0
  
  libavformat   52.23. 1 / 52.23. 1
  
  libavdevice   52. 1. 0 / 52. 1. 0
  
  libswscale     0. 6. 1 /  0. 6. 1
  
  built on Jan 13 2009 02:57:09, gcc: 4.2.4
  
  Input #0, image2, from 'pic\s%d.png':
  
  Duration: 00:03:53.00, start: 0.000000, bitrate: N/A
  
  Stream #0.0: Video: png, rgb24, 1366x768, 12.00 tb(r)
  
  Input #1, wav, from 'rmt.wav':
  
  Duration: 00:12:16.19, bitrate: 64 kb/s
  
  Stream #1.0: Audio: pcm_u8, 8000 Hz, mono, s16, 64 kb/s
  
  Stream #0.0: Video: mpeg1video, yuv420p, 1366x768, q=2-31, 200 kb/s, 25.00 tb(c)
  
  Stream #0.1: Audio: mp2, 8000 Hz, mono, s16, 64 kb/s
  
  Stream mapping:
  
  Stream #0.0 -> #0.0
  
  Stream #1.0 -> #0.1
  
  [mp2 @ 0x1738390]Sampling rate 8000 is not allowed in mp2
  
  Error while opening codec for output stream #0.1 - maybe incorrect parameters such as bit_rate, rate, width or height

• How do I extract color matrix from MP4 an x264 stream in Media Foundation

  23 août 2016, par Jules

  I am playing a video (mp4 containing x264 encoded video stream) with a custom player using media foundation.

  When I convert the YUV information into RGB I need to account for the color matrix and range used at encode time.

  Some of my videos have this information, I can use MediaInfo.exe or FFMPEG to see that it is present.

  However, for such videos if I look at the relevant Media Foundation properties (Extended Color Information) the properties are not present in the files.

  So, somehow I need to find a way to access the information.

  Media Foundation does provide access to MF_MT_MPEG4_SAMPLE_DESCRIPTION and MF_MT_MPEG_SEQUENCE_HEADER for the video stream but I can’t find descriptions of what these contain.

  I noticed that the MF_MT_MPEG_SEQUENCE_HEADER is much longer for the videos with the information present and this (MPEG Headers Quick Reference) seems to suggest headers might contain the information I need.

  I’m looking for Color Range (limited/full), Color Primaries, Transfer Characteristics and Matrix Coefficients (BT.709 etc).

  I’d greatly appreciate any help finding this information from a Media Foundation video stream.

  Thanks

  Jules

  ---

  Update - Sequence Header

  The sequence header appears to be a subset of MPEG4 sample description, though I can’t find anything that indicates what either bits of data actually contains / doesn’t contain specifically.

  The sequence header appears to contain data structured as an MP4 byte stream as described in the H264 Standards Document and includes the VUI (Video Usability Information - Annex E of document) which may then include the colour information I’m interested in.

  Given that it’s a byte stream I need to know where it starts and whether there’s some existing code I could use to decode it.

  In FFMPEG in libavcodec/h264_ps.c there is a function called ff_h264_decode_seq_parameter_set which ends up calling decode_vui_parameters. It seems possible that seq_parameter_set maps to MF_MT_MPEG_SEQUENCE_HEADER and it may be possible to use that code to decode the data.

  If anyone one has any direct experience with decoding this data it would be very useful.

  Thanks again

  ---

  Update - Related posts

  I found this How to decode sprop-parameter-sets in a H264 SDP ? and Possible Locations for Sequence/Picture Parameter Set(s) for H.264 Stream which are fairly helpful.

  The sequence header would appear to be Sequence or picture parameter set (pps) and the parameters I want are the VUI extension subset.

  Plus this post H.264 stream structure gives the high level of how the stream data is structured, and the MF_MT_MPEG_SEQUENCE_HEADER appears to start with a NAL 0x00 0x00 0x01 so I’m guessing it is a NAL containing the PPS.