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• When creating a Xing or Info tag in an MP3, may I use any MP3 header or does it have to match other frames ?

  13 décembre 2019, par Alexis Wilke

  I have a set of bare MP3 files. Bare as in I removed all tags (no ID3, no Xing, no Info) from those files.

  Just before sending one of these files to the client, I want to add an Info tag. All of my files are CBR so we will use an Info tag (no Xing).

  Right now I get the first 4 bytes of the existing MP3 to get the Version (MPEG-1, Layer III), Bitrate, Frequency, Stereo Mode, etc. and thus determine the size of one frame. I create the tag that way, reusing these 4 bytes for the Info tag and determining the size of the frame.

  For those wondering, these 4 bytes may look like this :

  FF FB 78 04

  To me it felt like you are expected to use the exact same first 4 bytes in the Info tag as found in the other audio frames of the MP3, but when using ffmpeg, they stick an Info tag with a hard coded header (wrong bitrate, wrong frequency, etc.)

  My question is : Is ffmpeg really doing it right ? (LAME doesn’t do that) Could I do the same, skipping the load of the first 4 bytes and still have the greater majority of the players out there play my files as expected ?

  Note : since I read these 4 bytes over the network, it would definitely save a lot of time and some bandwidth to not have to load these 4 bytes on a HEAD request. Resources I could use for the GET requests instead...

• avcodec/mpeg12dec : Limit maximum A53 CC size

  21 septembre 2020, par Michael Niedermayer

  avcodec/mpeg12dec : Limit maximum A53 CC size
  This is more than 10 times the size of the largest i found. And also alot more
  
  than our encoder could handle (our encoder is limited to max 31)
  
  Without any limit megabyte+ sized blocks can be reallocated millions of times.
  
  Sadly the SCTE-20 spec does not seem to contain any hard limit directly, so this limit here
  
  is arbitrary
  Fixes : Timeout (25sec -> 152ms)
  
  Fixes : 25714/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG2VIDEO_fuzzer-5713633336885248
  Found-by : continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/mpeg12dec.c

• Play same audio file to two different sound cards simultaneously using android media player [on hold]

  15 décembre 2016, par Hardik

  I have one custom board( media player) running android4.2 OS on it and I need to add a feature that will play same audio to two different sound cards simultaneously.

  I have two output devices HDMI and TLV320aic3100 Codec.
  And Want to play Video and audio through HDMI and same audio should play through TLV codec. Audio through TLV codec should be in sync with HDMI video/audio.

  Right now I’m able to play audio through TLV codec by hard-coding sound card number in tinyalsa PCM code "pcm.c" which is used by HAL code of Android Media Player (by default this code will give audio to HDMI),
  but not able to provide audio to both sound cards simultaneously.

  I tried with creating thread in pcm code and writing incoming audio data to both sound card, By doing this HDMI going into under-run problem.

  Is there any way to provide same audio to both sound cards simultaneously using Android Media Player or any other options to try ?