The NBA is engaged in serious discussions with the National Basketball Players Association and broadcast partners on sweeping and dramatic changes to the league calendar that would include a reseeding of the four conference finalists, a 30-team in-season tournament and a postseason play-in, league sources told ESPN.

These scenarios would include the shortening of the regular season to a minimum of 78 games, league sources said.

Discussions are progressing with hopes of bringing a vote to the April meeting of the league's Board of Governors that would introduce some -- if not all -- of these proposals into the NBA's 75th anniversary season of 2021-22, league sources said. The NBA still has work to do coordinating with constituents on the myriad implications involving the proposed changes.

The reseeding of teams in the semifinal round based on regular-season record could give the NBA a championship series that includes its best two teams. The WNBA has been seeding teams in the playoffs without regard to conference for several seasons.

Commissioner Adam Silver has been driving this agenda of change -- especially the in-season tournament cup modeled after European soccer -- for years. The NBA is selling the idea of lucrative television and sponsorship revenue that would drive long-term growth and combat stagnation in a rapidly splintering consumer environment.

The league is working to make sure the loss of revenue for teams and players with a shortened regular season would be break even or better initially, with significant financial windfalls in the long term.

The NBA cannot implement these changes without an agreement with the NBPA, and those talks have been ongoing between groups led by Silver and NBPA executive director Michele Roberts, league sources said.

In proposals that include adoption of in-season tournaments and post-season play-in, the traditional regular season schedule would be reduced from 82 games -- with most teams scheduled to play 78 or 79 games. There's an extremely limited possibility of a team playing a maximum of 83 games based on on possible tournament and play-in scenarios, league sources said. For the in-season tournament, the NBA is focused on 30-team participation that begins with a divisional group stage of scheduled regular-season games.

Those pre-knockout round games will be part of the regular-season schedule. Six divisional winners -- based on home and away records in the group stage -- and teams with the next two best records would advance to a single-elimination knockout round, league sources said.

Those teams could each potentially compete in the quarterfinals, semifinals and finals.

Proposals exist that would compensate players and coaches for advancing in and winning the tournament, league sources said. Even with possible passage, the NBA has no illusions that it will get the entire league to make an immediate enthusiastic commitment to the importance of competing for an in-season tournament championship, but it does believe that would come with time and tradition.

The NBA and NBPA are finding common ground on a post-Thanksgiving tournament window that would extend into mid-December, league sources said. Months ago, the NBA had proposed a late January-February tournament that would culminate with a Final Four during All-Star weekend, sources said. That idea faded fast. Both the union and team executives expressed concern over that idea. The NBPA was resistant to shortening players' All-Star breaks and requiring some to potentially participate in the in-season tournament and All-Star weekend.

Teams were concerned that roster turnover at the early February trade deadline and ensuing buyout/waiver window could compromise the integrity of the tournament.

As for timing, there was uncertainty whether holding the tournament in January would risk losing viewership and media attention to the NFL playoffs. Running into March would mean competing with college basketball. The post-Thanksgiving window gives the NBA the chance to compete against only conference bowl championships and less consequential early bowl games.

The NBA has been hesitant about shoehorning tournament games onto the Christmas Day schedule; the league (and its network partners, including ESPN and ABC) wants to make sure every Christmas game features elite teams and franchises from the biggest markets.

The play-in proposal is this: two four-team tournaments featuring the seventh, eighth, ninth and 10th seeds in each conference. The seventh seed would host the eighth seed, with the winner of that single game earning the seventh spot, league sources said.

The ninth seed would host the 10th seed, with the winner of that game facing the loser of the 7-versus-8 matchup for the final playoff spot.

Roberts and staff have been discussing league proposals extensively at the NBPA level and recently began bringing details of the league's calendar proposals to the broader membership on a team-by-team basis, sources said. Roberts and union officials meet with all 30 teams over the course of each regular season. These sessions with players are starting to take shape. As a high-ranking source said, "So far, there's been no real pushback."

For the NBA to achieve its goal of implementation of the proposed changes for the 2021-22 anniversary season, there's a clock on finding a framework that works for the teams, union and television partners before the April meeting of the Board of Governors, league sources said. Talks are ongoing, but legitimate and serious traction is emerging for dramatic change for the future of the NBA.

ESPN draft analyst Jonathan Givony contributed to this story.