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• Play MPEG-CENC encrypted local file on android

  26 mai 2018, par rd7773

  I need to decrypt and play a cenc-aes-ctr mp4 video on the fly which is locally stored on the device.
  The video was encrypted at server end by using following ffmpeg command and then downloaded to phone :

  ffmpeg -i SampleVideo_1280x720_1mb.mp4 -vcodec copy -acodec copy -encryption_scheme cenc-aes-ctr -encryption_key 76a6c65c5ea762046bd749a2e632ccbb -encryption_kid a7e61c373e219033c21091fa607bf3b8 SampleVideo_1280x720_1mb_encrypted.mp4

  It is successfully getting played with ffmpeg command :

  ffplay SampleVideo_1280x720_1mb_encrypted.mp4 -decryption_key 76a6c65c5ea762046bd749a2e632ccbb

  But I do not want to use ffmpeg in android so I am using libeasy library which creates a local http server to make a stream of offline video and then decrypt it on the fly using Cipher. The Cipher which is provided to the LocalHttpServer for decryption process, needs the initialisation vector (iv) for CTR mode which is not externally available to us.
  From above command it is clear that ffmpeg doesn’t require the IV for encryption or decryption to be passed but i guess internally it uses 8 byte random iv.

  This is how i am creating Cipher to pass to LocalHttpServer :

  final Cipher c = Cipher.getInstance("AES/CTR/NoPadding","BC);
  
  c.init(Cipher.DECRYPT_MODE, new SecretKeySpec(hexStringToBytes("76a6c65c5ea762046bd749a2e632ccbb"), "AES"), new IvParameterSpec(new byte[16]));

  So my question is, what value of iv should i pass in this case to Cipher ? My basic requirement is to play a offline MPEG-CENC encrypted mp4 video stored on device.
  Keeping in mind my very limited knowledge of cryptography, references to any library that provides such implementation with or without any tweaks is welcomed.

• How to set NTSC and CBR in ffmpeg ?

  14 mars 2024, par mvr rvm

  The parameters I aim to achieve are described below, but I'm unable to set a constant bitrate and the NTSC standard.

  


  General
ID/String                        : 1 (0x1)
Format/String                    : MPEG-TS
FileSize/String                  : 2.80 GiB
Duration/String                  : 1 h 28 min
OverallBitRate_Mode/String       : Constant
OverallBitRate/String            : 4 535 kb/s
FrameRate/String                 : 23.976 FPS
FileExtension_Invalid            : ts m2t m2s m4t m4s tmf ts tp trp ty

Video
ID                                       : 49 (0x31)
Menu ID                                  : 2 (0x2)
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L3.1
Format settings                          : CABAC / 3 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 3 frames
Format settings, GOP                     : M=3, N=23
Codec ID                                 : 27
Duration                                 : 1 h 28 min
Bit rate mode                            : Constant
Bit rate                                 : 4 000 kb/s
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 23.976 (24000/1001) FPS
Standard                                 : NTSC
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.181
Stream size                              : 2.43 GiB (86%)
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709


  


  Using the command :
ffmpeg -i input.mpg -codec:v libx264 -profile:v high -level 3.1 -coder 1 -pix_fmt yuv420p -r 24000/1001 -s 1280x720 -aspect 16:9 -x264-params "cabac=1:no-deblock=0:ref=3:weightp=2:bframes=3:b_pyramid=1:b-adapt=2:nal-hrd=cbr:bitrate=4M:minrate=4M:maxrate=4M:bufsize=8M" -color_range tv -color_primaries bt709 -color_trc bt709 -colorspace bt709 -c:a mp2 -b:a 128k -ac 2 -ar 44100 -f mpegts output.mpg

  


• Capturing PCM audio data stream into file, and playing stream via ffmpeg, how ?

  11 avril 2015, par icarus74

  Would like to do following four things (separately), and need a bit of help understanding how to approach this,

  1. Dump audio data (from a serial-over-USB port), encoded as PCM, 16-bit, 8kHz, little-endian, into a file (plain binary data dump, not into any container format). Can this approach be used :

     $ cat /dev/ttyUSB0 > somefile.dat

  Can I do a ^C to close the file writing, while the dumping is in progress, as per the above command ?

  2. Stream audio data (same as above described kind), directly into ffmpeg for it to play out ? Like this :

     $ cat /dev/ttyUSB0 | ffmpeg

  or, do I have to specify the device port as a "-source" ? If so, I couldn’t figure out the format.

  Note that, I’ve tried this,

  $ cat /dev/urandom | aplay

  which works as expected, by playing out white-noise..., but trying the following doesn’t help :

  $ cat /dev/ttyUSB1 | aplay -f S16_LE

  Even though, opening /dev/ttyUSB1 using picocom @ 115200bps, 8-bit, no parity, I do see gibbrish, indicating presence of audio data, exactly when I expect.

  3. Use the audio data dumped into the file, use as a source in ffmpeg ? If so how, because so far I get the impression that ffmpeg can read a file in standard containers.

  4. Use pre-recorded audio captured in any format (perhaps .mp3 or .wav) to be streamed by ffmpeg, into /dev/ttyUSB0 device. Should I be using this as a "-sink" parameter, or pipe into it or redirect into it ? Also, is it possible that in 2 terminal windows, I use ffmpeg to capture and transmit audio data from/into same device /dev/ttyUSB0, simultaneously ?

  My knowledge of digital audio recording/processing formats, codecs is somewhat limited, so not sure if what I am trying to do qualifies as working with ’raw’ audio or not ?

  If ffmpeg is unable to do what I am hoping to achieve, could gstreamer be the solution ?

  PS> If anyone thinks that the answer could be improved, please feel free to suggest specific points. Would be happy to add any detail requested, provided I have the information.