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• How to set segment duration of a DASH stream using ffmpeg ?

  25 juillet 2024, par ipartola

  I am trying to convert a video to a live DASH stream using ffmpeg. The command looks like this :

  


  ffmpeg -i input.mp4 -preset veryfast \
-c:v libx264 -pix_fmt yuv420p -map 0:v:0 \
-s:0 1280x720 -b:v:0 2M -maxrate:0 2.5M -bufsize:0 4M \
-use_template 1 -use_timeline 1 -seg_duration 1 -f dash foo/stream.mpd


  


  I would like to have the segment duration be 1 second long. However the above command seems to produce chunk files about 8 seconds long instead. However if I change the command to the following (adding -g 5) :

  


  ffmpeg -i input.mp4 -preset veryfast \
-c:v libx264 -pix_fmt yuv420p -map 0:v:0 \
-s:0 1280x720 -b:v:0 2M -maxrate:0 2.5M -bufsize:0 4M \
-g 5 \
-use_template 1 -use_timeline 1 -seg_duration 1 -f dash foo/stream.mpd


  


  I get chunk files that are much closer to 1 second long. Obviously this isn't ideal since that will produce a keyframe every 5 frames. So :

  


  a) I don't understand the relationship between seg_duration and keyframe interval. Why is ffmpeg not automatically just putting a keyframe at the beginning of each chunk ?

  


  b) How do I get the chunk/segment length I want ?

  


• Convert wav file from WAV_FORMAT_EXTENSIBLE to WAV_FORMAT_PCM

  22 juillet 2022, par michaeljan

  I have a 16-bit 44.1kHz wav file in WAV_FORMAT_EXTENSIBLE format. What is a simple and efficient way to convert it to WAV_FORMAT_PCM on the command-line ?

  


  In case it helps, here's a sample file. It's (a part of) a file that a client sent to me, so I'm not sure how it was created. But it is understood by ffmpeg and playable by VLC.

  


  Also, I've seen this question, but it's 7 years old and the accepted answer doesn't answer the question. Also, that question asks for ffmpeg-only solutions, whereas I am open to other command-line solutions as well. (Although I do prefer ffmpeg.)

  


• Matching a specific media format with ffmpeg/avconv

  5 mai 2020, par Markus A.

  I need to encode a video from static images in such a way that it format-matches another one so I can splice the video streams together.

  



  Here is the mediainfo of the file I'm trying to match :

  



  Video
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Baseline@L3.1
Format settings, CABAC                   : No
Format settings, ReFrames                : 1 frame
Codec ID                                 : 7
Duration                                 : 2mn 46s
Bit rate                                 : 1 614 Kbps
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Variable
Standard                                 : NTSC
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Stream size                              : 32.0 MiB (87%)
Color primaries                          : BT.601 PAL
Transfer characteristics                 : BT.601
Matrix coefficients                      : BT.601


  



  So far, what I have been able to come up with is the following :

  



  avconv -f image2 -framerate 1.2 -i loop_%d.tif -c:v libx264 -preset veryslow -profile:v baseline -level:v 31 -b:v 1614K -refs 1 loop.flv


  



  This gets me to :

  



  Video
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Baseline@L3.1
Format settings, CABAC                   : No
Format settings, ReFrames                : 1 frame
Codec ID                                 : 7
Duration                                 : 2s 917ms
Bit rate                                 : 1 614 Kbps
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 1.200 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 1.459
Stream size                              : 575 KiB
Writing library                          : x264 core 142 r2431 a5831aa
Encoding settings                        : cabac=0 / ref=1 / deblock=1:0:0 / analyse=0x1:0x131 / me=umh / subme=10 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=24 / chroma_me=1 / trellis=2 / 8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=6 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=0 / weightp=0 / keyint=250 / keyint_min=1 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=abr / mbtree=1 / bitrate=1614 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00


  



  Which, unfortunately, still isn't good enough as VLC Media Player crashes hard (just closes), logging main error: Failed to compensate for the format changes, removing all filters; main error: Failed to create video converter as soon as the stream splice occurs. I tried splicing another stream in that does have the exact same encoding, and it works fine. I'm also making sure to only splice on key-frames and I am including the NALU containing the AVCDecoderConfigRecord, so I'm pretty sure I'm not doing anything else wrong, especially since a couple other programs are fine with the splice. It's just VLC that expects an even closer match.

  



  Here are things I've tried :

  



  

  • Adding -vsync 2 to get variable frame rate mode. Doesn't change anything.

  


  • Adding -color_primaries bt470bg -color_trc gamma28 -colorspace bt470bg to try to get BT.601 PAL settings (several websites mentioned this). Doesn't change anything.

  


  • Adding -s ntsc to set the standard to NTSC. This also changes the resolution to 720x480 (not OK), and specifying -s 1280x720 in addition gets rid of the NTSC tag again.

  


  



  If anyone knows what flags I need to supply to get closer, that would be super-helpful ! The stream I'm trying to match is encoded on an Android device (it's a live-stream), so I'm assuming it is built using the standard Android MediaCoder framework, in case that helps.