When playing H264 video from a TS container, it seems the BUFFER_FLAG_KEY_FRAME in addition to being set on the actual IDR frames, is also wrongly set on each frame immediately preceding the IDR one.

In more detail the root cause seems to be the following. In streams with AUD, the consume at the beginning of the PES, on the AUD NAL, calls endNAlUnit() on the previous NAL (NAL_UNIT_TYPE_NON_IDR) and since randomAccessIndicator is set, this causes treatIFrameAsKeyframe to be true and so sampleIsKeyframe to be set while still on the previous sample (outputSample has not been called yet). The following NAL unit (SPS) causes endNAlUnit() to be called on the SampleReader for the AUD NAL which calls outputSample on the previous sample with sampleIsKeyframe wrongly set.

The proposed solution, with this PR, is to pass the randomAccessIndicator parameter in SampleReader in the startNalUnit() instead of the endNalUnit() and have it as a class variable in the SampleReader. With this change the randomAccessIndicator would only depend on the PES the current NAL belongs to and the issue described above would be resolved.