+/**
+ * Parse NAL units of found picture and decode some basic information.
+ *
+ * @param s parser context.
+ * @param avctx codec context.
+ * @param buf buffer with field/frame data.
+ * @param buf_size size of the buffer.
+ */
+static inline int parse_nal_units(AVCodecParserContext *s,
+ AVCodecContext *avctx,
+ const uint8_t *buf, int buf_size)
+{
+ H264Context *h = s->priv_data;
+ const uint8_t *buf_end = buf + buf_size;
+ unsigned int pps_id;
+ unsigned int slice_type;
+ int state = -1;
+ const uint8_t *ptr;
+
+ /* set some sane default values */
+ s->pict_type = AV_PICTURE_TYPE_I;
+ s->key_frame = 0;
+
+ h->s.avctx= avctx;
+ h->sei_recovery_frame_cnt = -1;
+ h->sei_dpb_output_delay = 0;
+ h->sei_cpb_removal_delay = -1;
+ h->sei_buffering_period_present = 0;
+
+ if (!buf_size)
+ return 0;
+
+ for(;;) {
+ int src_length, dst_length, consumed;
+ buf = avpriv_mpv_find_start_code(buf, buf_end, &state);
+ if(buf >= buf_end)
+ break;
+ --buf;
+ src_length = buf_end - buf;
+ switch (state & 0x1f) {
+ case NAL_SLICE:
+ case NAL_IDR_SLICE:
+ // Do not walk the whole buffer just to decode slice header
+ if (src_length > 20)
+ src_length = 20;
+ break;
+ }
+ ptr= ff_h264_decode_nal(h, buf, &dst_length, &consumed, src_length);
+ if (ptr==NULL || dst_length < 0)
+ break;
+
+ init_get_bits(&h->s.gb, ptr, 8*dst_length);
+ switch(h->nal_unit_type) {
+ case NAL_SPS:
+ ff_h264_decode_seq_parameter_set(h);
+ break;
+ case NAL_PPS:
+ ff_h264_decode_picture_parameter_set(h, h->s.gb.size_in_bits);
+ break;
+ case NAL_SEI:
+ ff_h264_decode_sei(h);
+ break;
+ case NAL_IDR_SLICE:
+ s->key_frame = 1;
+ /* fall through */
+ case NAL_SLICE:
+ get_ue_golomb(&h->s.gb); // skip first_mb_in_slice
+ slice_type = get_ue_golomb_31(&h->s.gb);
+ s->pict_type = golomb_to_pict_type[slice_type % 5];
+ if (h->sei_recovery_frame_cnt >= 0) {
+ /* key frame, since recovery_frame_cnt is set */
+ s->key_frame = 1;
+ }
+ pps_id= get_ue_golomb(&h->s.gb);
+ if(pps_id>=MAX_PPS_COUNT) {
+ av_log(h->s.avctx, AV_LOG_ERROR, "pps_id out of range\n");
+ return -1;
+ }
+ if(!h->pps_buffers[pps_id]) {
+ av_log(h->s.avctx, AV_LOG_ERROR, "non-existing PPS referenced\n");
+ return -1;
+ }
+ h->pps= *h->pps_buffers[pps_id];
+ if(!h->sps_buffers[h->pps.sps_id]) {
+ av_log(h->s.avctx, AV_LOG_ERROR, "non-existing SPS referenced\n");
+ return -1;
+ }
+ h->sps = *h->sps_buffers[h->pps.sps_id];
+ h->frame_num = get_bits(&h->s.gb, h->sps.log2_max_frame_num);
+
+ avctx->profile = ff_h264_get_profile(&h->sps);
+ avctx->level = h->sps.level_idc;
+
+ if(h->sps.frame_mbs_only_flag){
+ h->s.picture_structure= PICT_FRAME;
+ }else{
+ if(get_bits1(&h->s.gb)) { //field_pic_flag
+ h->s.picture_structure= PICT_TOP_FIELD + get_bits1(&h->s.gb); //bottom_field_flag
+ } else {
+ h->s.picture_structure= PICT_FRAME;
+ }
+ }
+
+ if(h->sps.pic_struct_present_flag) {
+ switch (h->sei_pic_struct) {
+ case SEI_PIC_STRUCT_TOP_FIELD:
+ case SEI_PIC_STRUCT_BOTTOM_FIELD:
+ s->repeat_pict = 0;
+ break;
+ case SEI_PIC_STRUCT_FRAME:
+ case SEI_PIC_STRUCT_TOP_BOTTOM:
+ case SEI_PIC_STRUCT_BOTTOM_TOP:
+ s->repeat_pict = 1;
+ break;
+ case SEI_PIC_STRUCT_TOP_BOTTOM_TOP:
+ case SEI_PIC_STRUCT_BOTTOM_TOP_BOTTOM:
+ s->repeat_pict = 2;
+ break;
+ case SEI_PIC_STRUCT_FRAME_DOUBLING:
+ s->repeat_pict = 3;
+ break;
+ case SEI_PIC_STRUCT_FRAME_TRIPLING:
+ s->repeat_pict = 5;
+ break;
+ default:
+ s->repeat_pict = h->s.picture_structure == PICT_FRAME ? 1 : 0;
+ break;
+ }
+ } else {
+ s->repeat_pict = h->s.picture_structure == PICT_FRAME ? 1 : 0;
+ }
+
+ return 0; /* no need to evaluate the rest */
+ }
+ buf += consumed;
+ }
+ /* didn't find a picture! */
+ av_log(h->s.avctx, AV_LOG_ERROR, "missing picture in access unit\n");
+ return -1;
+}
+