HTTP Streaming with Encryption under Linux

For a customer of ours, we need to mass encode thousands of video files and also segment and encrypt them for use with Apple’s HTTP Streaming.

For a customer of ours, we need to mass encode thousands of video files and also segment and encrypt them for use with Apple’s HTTP Streaming. (using Amazon EC2 instances for the leg work).

On his blog, Carson McDonald, has put together a good over view of how HTTP Streaming can work under Linux a long with a segmenter.

The one piece of the jigsaw we were missing was encryption and after some work ourselves and with the help of a stackoverflow question, we have a working sequence of commands to successfully and compatibly encrypt segments for playback on Safari and other supported HTTP streaming clients:

  1. Create a key file:
  2. Convert the key into hex:
  3. At this point, let’s assume we have segmented a file of 30 seconds called video_low.ts into ten 3 second segments called video_low_X.ts where X is an integer from 1 to 10. We can then encrypt these as follows:

With a matching m3u8 file such as the following, the above worked fine:

What caught us out was the initialisation vector with is described in the draft IETF document as follows:

128-bit AES requires the same 16-octet Initialization Vector (IV) to
be supplied when encrypting and decrypting. Varying this IV
increases the strength of the cipher.

If the EXT-X-KEY tag has the IV attribute, implementations MUST
use the attribute value as the IV when encrypting or decrypting
with that key. The value MUST be interpreted as a 128-bit
hexadecimal number and MUST be prefixed with 0x or 0X.

If the EXT-X-KEY tag does not have the IV attribute,
implementations MUST use the sequence number of the media
file as the IV when encrypting or decrypting that media file.
The big-endian binary representation of the sequence number
SHALL be placed in a 16-octet buffer and padded (on the left)
with zeros.

Encoding Full HD as FLV (for Gallery3)

I have a full HD camcorder and I wanted to stick some good quality video on my gallery for relatives to view. So, I needed to convert my sample 100MB MP4 full HD file to a suitably sized FLV for the Gallery. Here’s what I did…

I have a very nice Samsung R10 Full HD Camcorder which I bought last year. After a recent family holiday, I wanted to stick some good quality video on my gallery for relatives to view. The gallery is RC2 of the excellent Gallery 3 package which uses another excellent open source tool called Flow Player to play movies.

So, I needed to convert my test 100MB MP4 full HD file to a suitably sized FLV for the Gallery. My initial attempts with ffmpeg worked fine but the quality (sample) was very poor and changing the bit rate in different ways seemed to make no difference:

I then turned to x264 and broke the process down to a number of stages:

  1. Extract the raw video to YUV4MPEG (this creates a 7GB file from my 100MB MP4):
  2. Encode the video component to H.264/FLV at the specified bit rate with good quality:

    Note that I’m using the veryslow preset which is… very slow! You can use other presets as explained in the x264 man page.
  3. Extract and convert the audio component to MP3 (the sample rate is important):
  4. Merge the converted audio and video back together:

    This yields a near perfect encoding at 22MB. It’s still full size though (HD at 1920×1080).
  5. The last step is to then use ffmpeg to resize the video and it now seems to respect bit rate parameters:

The resultant video can be seen here.

Robert Swain has a useful guide for ffmpeg x264 encoding.