[Spice-devel] [PATCH spice-html5] Review the webm audio track header and remove the fixmes.

[Pavel Grunt]

Ack

Thanks,
Pavel

On Fri, 2016-12-23 at 10:53 -0600, Jeremy White wrote:
> This involved a review of the Firefox parsing code along
> with the official specifcation, and setting these fields
> to the specified default values.
> 
> Most notably, I have found that recent browsers do not need the
> 8 ms pre skip, and it seems to remove some audio lag to
> switch to 0.
> 
> Signed-off-by: Jeremy White <jwhite at codeweavers.com>
> ---
>  webm.js | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/webm.js b/webm.js
> index 789da14..72c1853 100644
> --- a/webm.js
> +++ b/webm.js
> @@ -393,28 +393,39 @@ webm_SeekHead.prototype =
>  
>  function webm_AudioTrackEntry()
>  {
> +    /*
> +    ** In general, we follow this specification:
> +    **   https://www.matroska.org/technical/specs/index.html
> +    ** we supply the mandatory values, and a comment notes
> +    ** where we differ from the default
> +    **   There is one RECOMMENDED guideline we are omitting;
> +    ** the OPUS codec_delay is recommended to be 80ms.
> +    ** However, the spice server does not currently provide time
> +    ** stamps that are offset by 80ms, so you effectively get an
> +    ** 80ms lag with this setting.
> +    */
>      this.id = WEBM_TRACK_ENTRY;
>      this.number = 1;
>      this.uid = 1;
>      this.type = 2; // Audio
>      this.flag_enabled = 1;
>      this.flag_default = 1;
> -    this.flag_forced = 1;
> -    this.flag_lacing = 0;
> -    this.min_cache = 0; // fixme - check
> +    this.flag_forced = 1;  // Different than default; we wish to
> force
> +    this.flag_lacing = 1;
> +    this.min_cache = 0;
>      this.max_block_addition_id = 0;
> -    this.codec_decode_all = 0; // fixme - check
> -    this.seek_pre_roll = 0; // 80000000; // fixme - check
> -    this.codec_delay =   80000000; // Must match
> codec_private.preskip
> +    this.seek_pre_roll = 0;
> +    this.codec_delay =   0; // Must match codec_private.preskip
>      this.codec_id = "A_OPUS";
> +    this.codec_decode_all = 1;
>      this.audio = new webm_Audio(OPUS_FREQUENCY);
>  
>      // See:  http://tools.ietf.org/html/draft-terriberry-oggopus-01
>      this.codec_private = [ 0x4f, 0x70, 0x75, 0x73, 0x48, 0x65,
> 0x61, 0x64,  // OpusHead
>                             0x01, // Version
>                             OPUS_CHANNELS,
> -                           0x00, 0x0F, // Preskip - 3840 samples -
> should be 8ms at 48kHz
> -                           0x80, 0xbb, 0x00, 0x00,  // 48000
> +                           0x00, 0x00, // Preskip - 3840 samples
> would be 8ms at 48kHz
> +                           0x80, 0xbb, 0x00, 0x00,  // nominal rate
> - 48000
>                             0x00, 0x00, // Output gain
>                             0x00  // Channel mapping family
>                             ];