uint32_t KeyframeSequencer::AddBytes(
const uint8_t *bytes,
const uint32_t byte_count,
const int64_t stream_offset) /* throw() */
{
const uint8_t *local_bytes = bytes;
const uint8_t *local_bytes_end = bytes + byte_count;
state_changed = false;
while (local_bytes < local_bytes_end)
{
local_bytes = ff_find_start_code(local_bytes, local_bytes_end,
&sync_accumulator);
if ((sync_accumulator & 0xffffff00) == 0x00000100)
{
uint8_t k = *(local_bytes-1);
sync_stream_offset = stream_offset;
keyframe = false;
KeyframePredicate(k);
first_NAL_byte = k;
return local_bytes - bytes;
}
}
return local_bytes - bytes;
}
/** \fn DTVRecorder::FindMPEG2Keyframes(const TSPacket* tspacket)
* \brief Locates the keyframes and saves them to the position map.
*
* This searches for three magic integers in the stream.
* The picture start code 0x00000100, the GOP code 0x000001B8,
* and the sequence start code 0x000001B3. The GOP code is
* prefered, but is only required of MPEG1 streams, the
* sequence start code is a decent fallback for MPEG2
* streams, and if all else fails we just look for the picture
* start codes and call every 16th frame a keyframe.
*
* NOTE: This does not only find keyframes but also tracks the
* total frames as well. At least a couple times seeking
* has been broken by short-circuiting the search once
* a keyframe stream id has been found. This may work on
* some channels, but will break on others so algorithmic
* optimizations should be done with great care.
*
* \code
* PES header format
* byte 0 byte 1 byte 2 byte 3 [byte 4 byte 5]
* 0x00 0x00 0x01 PESStreamID PES packet length
* \endcode
*
* \return Returns true if packet[s] should be output.
*/
bool DTVRecorder::FindMPEG2Keyframes(const TSPacket* tspacket)
{
bool haveBufferedData = !_payload_buffer.empty();
if (!tspacket->HasPayload()) // no payload to scan
return !haveBufferedData;
if (!ringBuffer)
return !haveBufferedData;
// if packet contains start of PES packet, start
// looking for first byte of MPEG start code (3 bytes 0 0 1)
// otherwise, pick up search where we left off.
const bool payloadStart = tspacket->PayloadStart();
_start_code = (payloadStart) ? 0xffffffff : _start_code;
// Just make these local for efficiency reasons (gcc not so smart..)
const uint maxKFD = kMaxKeyFrameDistance;
bool hasFrame = false;
bool hasKeyFrame = false;
// Scan for PES header codes; specifically picture_start
// sequence_start (SEQ) and group_start (GOP).
// 00 00 01 00: picture_start_code
// 00 00 01 B8: group_start_code
// 00 00 01 B3: seq_start_code
// (there are others that we don't care about)
const uint8_t *bufptr = tspacket->data() + tspacket->AFCOffset();
const uint8_t *bufend = tspacket->data() + TSPacket::SIZE;
while (bufptr < bufend)
{
bufptr = ff_find_start_code(bufptr, bufend, &_start_code);
if ((_start_code & 0xffffff00) == 0x00000100)
{
// At this point we have seen the start code 0 0 1
// the next byte will be the PES packet stream id.
const int stream_id = _start_code & 0x000000ff;
if (PESStreamID::PictureStartCode == stream_id)
hasFrame = true;
else if (PESStreamID::GOPStartCode == stream_id)
{
_last_gop_seen = _frames_seen_count;
hasKeyFrame |= true;
}
else if (PESStreamID::SequenceStartCode == stream_id)
{
_last_seq_seen = _frames_seen_count;
hasKeyFrame |= (_last_gop_seen + maxKFD)<_frames_seen_count;
}
}
}
if (hasFrame && !hasKeyFrame)
{
// If we have seen kMaxKeyFrameDistance frames since the
// last GOP or SEQ stream_id, then pretend this picture
// is a keyframe. We may get artifacts but at least
// we will be able to skip frames.
hasKeyFrame = !(_frames_seen_count & 0xf);
hasKeyFrame &= (_last_gop_seen + maxKFD) < _frames_seen_count;
hasKeyFrame &= (_last_seq_seen + maxKFD) < _frames_seen_count;
}
if (hasKeyFrame)
{
_last_keyframe_seen = _frames_seen_count;
HandleKeyframe();
}
if (hasFrame)
{
_frames_seen_count++;
if (!_wait_for_keyframe_option || _first_keyframe>=0)
_frames_written_count++;
}
return hasKeyFrame || (_payload_buffer.size() >= (188*50));
}
