- WebVttMediaParser uses WebVttSampleConverter to generate non
overlapping media samples.
- The media samples contains ISO BMFF boxes.
- Add kCodecWebVtt to signal that the media is webvtt and
the samples will be in ISO BMFF boxes.
Change-Id: I639902cdba7b04af75428bc20622e26b8203cfb2
Since the |extra_data| field contains codec-specific configuration
data, it makes sense to call it |codec_config|.
Change-Id: If9e35165a00fe82628cf931df397a8ef06505b0d