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• Modify H.264 Level in MP4 stream

  25 mars 2013, par d33pika

  I have 1000+ videos with wrong Level information, and hence do not play on some devices. They are H.264 baseline with aac audio in mp4 container. I want to correct them but avoid re-encoding. Am I right in assuming that this is possible and will be faster ? How do I identify the level_idc bits in the streams ? Will all streams have them in the same location ? I expect this to be in just one place in the stream, is this assumption correct ?
  Update : I came across a windows executable link that claims to do this. I want to be able to do this commandline on unix, so I can script it.

  More Updates : As per Roman's answer below. I dug up MP4 syntax and found that Profile and Level information are part of avcC atom under stsd. I could see that level was set to 1E, I corrected it to 1F. Before :

  61 76 63 43 01 42 C0 1E FF E1 00 19 67 42 C0 1E
D9

  After :

  61 76 63 43 01 42 C0 1F FF E1 00 19 67 42 C0 1E
D9

  with that the MediaInfo changed to :

  Video
  
  ID                                       : 1
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : Baseline@L3.0
  
  Format settings, CABAC                   : No
  
  Format settings, ReFrames                : 3 frames
  
  Muxing mode                              : Container profile=Baseline@3.1
  
  Codec ID                                 : avc1
  
  Codec ID/Info                            : Advanced Video Coding
  
  Duration                                 : 1mn 4s
  
  Bit rate                                 : 3 000 Kbps
  
  Width                                    : 1 280 pixels
  
  Height                                   : 720 pixels
  
  Display aspect ratio                     : 16:9
  
  Frame rate mode                          : Constant
  
  Frame rate                               : 30.000 fps
  
  Color space                              : YUV
  
  Chroma subsampling                       : 4:2:0
  
  Bit depth                                : 8 bits
  
  Scan type                                : Progressive
  
  Bits/(Pixel*Frame)                       : 0.109
  
  Stream size                              : 22.7 MiB (92%)
  
  Writing library                          : x264 core 120 r2151 a3f4407
  
  Encoding settings                        : cabac=0 / ref=3 / deblock=1:0:0 / analyse=0x1:0x111 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=0 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=12 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=0 / weightp=0 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=abr / mbtree=1 / bitrate=3000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00 

  It introduced a Muxing mode parameter with level 3.1 but alas this stream did not play on the device either. How do I correct the level indicated in Format Profile Is this possible without re-encoding ?

• During transcoding, does output quality of a video improve when i give output bitrate more than input video's bitrate ?

  19 septembre 2013, par Jobin Jose

  I use ffmpeg for converting videos.
  As i understand, the bitrate of a video stream is the number of bits which constitute the video over 1 second of time.
  What happens when i specify the output video bitrate to be more than the input video's bitrate ?
  For example :
  If bitrate of "Input.mp4" is 2000KBps and i want to convert it to "Output.mp4" with output bitrate set to 3000KBps.
  How will the converter create the extra 1000 bits(3000-2000) for every second of video ?

• Revision 0d0ed6a29b : Allow sub8x8 intra modes test for alt frame coding This commit allows sub8x8 in

  5 octobre 2013, par Jingning Han

  Changed Paths :
   Modify /vp9/encoder/vp9_onyx_if.c

  
  
  Allow sub8x8 intra modes test for alt frame coding

  This commit allows sub8x8 intra modes test in the rate-distortion
  loop for hd sequences in speed 1 and 2.

  For sequence y90n of hd set at 8000 kbps, speed 2 runtime goes
  from 207s to 210s. For ped_1080p at 3000 kbps, speed 2 runtim goes
  from 336s to 337s. Both are running with 300 frames.

  This improves compression performance by 0.24% for stdhd and 0.32%
  for hd.

  Change-Id : I173ca38a6411565ae6cfadd184c42b2070c5de1f